Merge PR #110: feat(frontend): mobile-friendly temperature charts with a fixed readout

Replace the floating recharts tooltip, which covered the plot on a phone, with
toggle chips and a readout row above a plain SVG chart that scrubs by touch.
The four series are CWU, Bufor CO, Do pompy and Wyjście pompy; indoor and
outdoor temperature are dropped from the charts.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.claude/skills/close-milestone/SKILL.md

@@ -0,0 +1,19 @@
+---
+name: close-milestone
+description: Close the current milestone in docs/roadmap.md, remove its working notes and start the next one. Use when every item of the current milestone is done.
+---
+
+# Close milestone
+
+1. Read `docs/roadmap.md`. Every item of "Current" is checked and its "Done when" holds.
+   Anything you cannot verify yourself (e.g. "a week on the Pi") you ask the user about.
+   Stop and report if something is open.
+2. Branch `docs/close-<milestone>` (e.g. `docs/close-m1`).
+3. Under "Done", add one line: `- M<n> <name> · <tag or commit>: <what it delivered>`.
+   Remove the "Current" checklist and any placeholder line.
+4. Remove the milestone's working notes: fixed defects (D…), consumed feasibility checks,
+   notes that served only this milestone. Verified knowledge moves first: controller facts
+   to `docs/frisko/`, scope or architecture to `docs/spec.md`, decisions to a new ADR.
+5. Make the next row of "Next" the new "Current": a checklist of PR-sized items in build
+   order, keeping its "Done when". Ask the user when the split is not obvious.
+6. `scripts/check.sh` (roadmap ≤ 80 lines), then `/ship`.

.claude/skills/ship/SKILL.md

@@ -0,0 +1,32 @@
+---
+name: ship
+description: Take the current topic branch to master through a Gitea PR with green CI, then optionally release it and update the Pi. Use when a change is ready to merge or release.
+---
+
+# Ship
+
+Repo rules: `CONTRIBUTING.md`. Gitea: https://git.mariuszpacek.pl/mariusz.pacek/home-pump
+(no API token here; reads need none).
+
+1. On a topic branch (`feat/`, `fix/`, `docs/`, `chore/`, `refactor/`), clean tree, commits
+   in Conventional Commits. Run `scripts/check.sh`.
+2. `git push -u origin <branch>`; CI runs on every pushed branch.
+3. Open the PR by push (Gitea AGit), title in Conventional Commits, description says why:
+   `git push origin HEAD:refs/for/master -o topic=<branch> -o title="…" -o description="…"`.
+   The description is one line (push options cannot hold newlines). After later fixes push
+   both the branch and `refs/for/master` with the same topic, so CI and the PR both update.
+   If that is refused, give the user the compare link `…/compare/master...<branch>`.
+4. Wait for CI on the head commit, polling every 30 s:
+   `curl -s …/api/v1/repos/mariusz.pacek/home-pump/commits/<sha>/status` → `state`.
+   On `failure`, read the run under `…/actions`, fix, push again. Never merge red.
+5. Merge only if the user asked for it in this task:
+   `git switch master && git pull --ff-only && git merge --no-ff <branch> -m "Merge PR #N: <title>"`,
+   then `git push origin master` and delete the branch locally and on origin. Confirm CI is
+   green on master. Gitea does not close an AGit PR merged by hand: ask the user to close it.
+6. Release and update only with the user's explicit approval for this one:
+   `scripts/release.sh vMAJOR.MINOR.PATCH` (patch for fixes, minor for features) waits for green
+   CI on master's head (no local check run), then tags master;
+   wait until the Release run under `…/actions` is green (it publishes the images). Then on the
+   Pi (`ssh <host>`, an alias while D7 is open): `cd /home/pi/home-pump && ./update.sh <version>`,
+   watch `journalctl -t home-pump-gateway -f` and Grafana for one polling cycle (300 s) and
+   report what you saw. Backend and frontend reach Kraków through Arcane (homelab-compose).

.gitea/workflows/ci.yml

@@ -0,0 +1,33 @@
+# One job: check.sh builds the three parts in parallel itself. The runner runs one job at a time
+# and its actions cache server is unreachable from job containers (ETIMEDOUT), so separate jobs
+# or setup-java/setup-node caches would only add waiting.
+name: CI
+
+on:
+  push:
+    branches:
+      - "**"
+
+jobs:
+  check:
+    name: Check (gateway, backend, frontend)
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      - name: Set up Java 21
+        uses: actions/setup-java@v5
+        with:
+          distribution: temurin
+          java-version: '21'
+      - name: Set up Maven
+        uses: stCarolas/setup-maven@v5
+        with:
+          maven-version: 3.9.6
+      - name: Set up Node
+        uses: actions/setup-node@v4
+        with:
+          node-version: '24'
+      - name: Check
+        run: scripts/check.sh

.gitea/workflows/release.yml

@@ -0,0 +1,56 @@
+# A pushed tag vMAJOR.MINOR.PATCH (scripts/release.sh) publishes the three images under that name
+# and as latest. The Pi pulls the gateway with gateway/update.sh; Kraków runs backend and frontend.
+name: Release
+
+on:
+  push:
+    tags:
+      - "v*.*.*"
+
+env:
+  REGISTRY: git.mariuszpacek.pl
+  IMAGES: git.mariuszpacek.pl/mariusz.pacek/home-pump
+
+jobs:
+  images:
+    name: Image (${{ matrix.part }})
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          # The Pi is arm64. Each Dockerfile builds on the runner's platform and only copies into
+          # the final stage, so the arm64 image needs no emulation.
+          - part: gateway
+            platforms: linux/arm64,linux/amd64
+          - part: backend
+            platforms: linux/amd64
+          - part: frontend
+            platforms: linux/amd64
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      # As in homelab-upgrade: the job talks to VM103's daemon through the mounted socket.
+      - name: Docker CLI
+        run: command -v docker >/dev/null || (apt-get update -qq && apt-get install -y -qq docker.io >/dev/null); docker version --format '{{.Client.Version}} -> {{.Server.Version}}'
+      - name: Set up Buildx
+        uses: docker/setup-buildx-action@v3
+      - name: Log in to the Gitea registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ gitea.repository_owner }}
+          # The owner's token with package write access (the secret homelab-upgrade uses too).
+          password: ${{ secrets.REGISTRY_TOKEN }}
+      # The registry cache keeps the Maven and npm layers between releases.
+      - name: Build and push
+        uses: docker/build-push-action@v6
+        with:
+          context: ${{ matrix.part }}
+          build-args: VERSION=${{ gitea.ref_name }}
+          platforms: ${{ matrix.platforms }}
+          push: true
+          tags: ${{ env.IMAGES }}-${{ matrix.part }}:${{ gitea.ref_name }},${{ env.IMAGES }}-${{ matrix.part }}:latest
+          cache-from: type=registry,ref=${{ env.IMAGES }}-${{ matrix.part }}:buildcache
+          cache-to: type=registry,ref=${{ env.IMAGES }}-${{ matrix.part }}:buildcache,mode=max

.githooks/pre-push

@@ -0,0 +1,3 @@
+#!/usr/bin/env bash
+# Enabled once per clone: git config core.hooksPath .githooks
+exec "$(git rev-parse --show-toplevel)/scripts/check.sh"

.gitignore

@@ -4,9 +4,10 @@
 .settings/
 
 # Intellij
-.idea/
+.idea
 *.iml
 *.iws
+.vscode
 
 # Mac
 .DS_Store
@@ -14,3 +15,46 @@
 # Maven
 log/
 target/
+/.idea/
+/.vscode/
+/.java-version
+dependency-reduced-pom.xml
+/workspace.code-workspace
+/target/
+
+# Node / frontend
+/node_modules/
+/frontend/node_modules/
+/frontend/dist/
+/dist/
+
+# Vite
+/.vite/
+
+# Env files
+.env
+.env.local
+.env.*.local
+
+# Logs
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+pnpm-debug.log*
+*.log
+logs/
+
+# Build / coverage
+build/
+coverage/
+
+# Misc
+.DS_Store
+
+# Large or legacy folders (not tracked)
+/apk/
+/old/
+/old_backup/
+
+# Agent worktrees
+/.claude/worktrees/

.gitlab-ci.yml

@@ -1,3 +0,0 @@
-# This file is a template, and might need editing before it works on your project.
-include:
-  template: Jobs/Code-Quality.gitlab-ci.yml

.idea/.gitignore

@@ -1,8 +0,0 @@
-# Default ignored files
-/shelf/
-/workspace.xml
-# Datasource local storage ignored files
-/dataSources/
-/dataSources.local.xml
-# Editor-based HTTP Client requests
-/httpRequests/

.idea/codeStyles/Project.xml

@@ -1,7 +0,0 @@
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-  <code_scheme name="Project" version="173">
-    <ScalaCodeStyleSettings>
-      <option name="MULTILINE_STRING_CLOSING_QUOTES_ON_NEW_LINE" value="true" />
-    </ScalaCodeStyleSettings>
-  </code_scheme>
-</component>

.idea/codeStyles/codeStyleConfig.xml

@@ -1,5 +0,0 @@
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-  <state>
-    <option name="PREFERRED_PROJECT_CODE_STYLE" value="Default" />
-  </state>
-</component>

.idea/compiler.xml

@@ -1,14 +0,0 @@
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-      <profile name="Maven default annotation processors profile" enabled="true">
-        <sourceOutputDir name="target/generated-sources/annotations" />
-        <sourceTestOutputDir name="target/generated-test-sources/test-annotations" />
-        <outputRelativeToContentRoot value="true" />
-        <module name="test.com" />
-      </profile>
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-</project>

.idea/inspectionProfiles/Project_Default.xml

@@ -1,116 +0,0 @@
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.idea/jarRepositories.xml

@@ -1,30 +0,0 @@
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-    <remote-repository>
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-      <option name="url" value="https://maven.mangoautomation.net/repository/ias-snapshot/" />
-    </remote-repository>
-    <remote-repository>
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-      <option name="name" value="Maven Central repository" />
-      <option name="url" value="https://repo1.maven.org/maven2" />
-    </remote-repository>
-    <remote-repository>
-      <option name="id" value="jboss.community" />
-      <option name="name" value="JBoss Community repository" />
-      <option name="url" value="https://repository.jboss.org/nexus/content/repositories/public/" />
-    </remote-repository>
-    <remote-repository>
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-      <option name="url" value="https://maven.mangoautomation.net/repository/ias-release/" />
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.idea/misc.xml

@@ -1,14 +0,0 @@
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.idea/test.com.iml

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.idea/vcs.xml

@@ -1,6 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<project version="4">
-  <component name="VcsDirectoryMappings">
-    <mapping directory="" vcs="Git" />
-  </component>
-</project>

.vscode/settings.json

@@ -1,4 +0,0 @@
-{
-    "java.compile.nullAnalysis.mode": "automatic",
-    "java.configuration.updateBuildConfiguration": "automatic"
-}

CLAUDE.md

@@ -0,0 +1,16 @@
+Backend for controlling the heat pump in Krosno (Frisko controller, Modbus TCP) from a phone.
+
+@CONTRIBUTING.md
+
+## For agents
+
+- Start from `docs/roadmap.md`; stay within the current milestone unless asked.
+- Read `docs/spec.md` and a decision in `docs/decisions/` only when the task touches it.
+- Production: `pi@raspberrypi.local`, the gateway in Docker (`gateway/compose.yaml`; until it is
+  installed, the old `home-pump.service`). Read-only inspection is fine; installing, updating,
+  restarting or changing files on the Pi needs explicit approval each time.
+- The Pi also runs `rpi-measurements.service` (house meter and BME280 into Influx); do not break
+  it. It moves into the gateway in M1; never run both against the meter at once. Do not upgrade
+  or reinstall the Pi's OS.
+- Never write to the controller `192.168.0.150` and never to the `Dom_Pompa` database.
+- Ask before force-pushing or rewriting history on Gitea.

CONTRIBUTING.md

@@ -0,0 +1,62 @@
+# Repository rules
+
+What we build: [docs/spec.md](docs/spec.md). Plan: [docs/roadmap.md](docs/roadmap.md).
+Reasons: [docs/decisions/](docs/decisions/).
+
+## Branches and pull requests
+
+- `master` is always deployable and matches what runs on the Pi.
+- Every change goes through a pull request on Gitea; no direct commits to `master`.
+- Branch names: `feat/…`, `fix/…`, `docs/…`, `chore/…`, `refactor/…`.
+- One topic per PR, small enough to review in one sitting. Merge only with green CI.
+- `archive/spring-boot-attempt` is reference only. Never merge it.
+
+## Commits
+
+- English, Conventional Commits: `fix(health): restart without /health polling`.
+- Imperative subject ≤ 72 characters; the body says why when it is not obvious.
+- Each commit builds and passes tests.
+
+## Code
+
+- Three parts, each with its `Dockerfile` and `compose.yaml` (ADR-010): `gateway/` and `backend/`
+  in Java 21 with Maven and no framework (ADR-001), `frontend/` in React and TypeScript (ADR-008).
+- `scripts/check.sh` is the gate: doc limits, secret scan, build and tests. CI runs it, and so
+  does the pre-push hook once enabled with `git config core.hooksPath .githooks`.
+- Readable first: small classes and methods, names from the domain, comments only for the why.
+- No dead code, no unused config, no duplicated logic, no speculative abstractions.
+- Every behaviour change has a test. Modbus is tested against `MockModbusServer` only.
+
+## Safety
+
+- Tests and local runs never use the real controller or the `Dom_Pompa` database.
+- A register is written only if it is on the allowlist (min, max, step) and verified in
+  `docs/frisko/`.
+- Changes to how or when we write to the controller need a test of the failure case.
+
+## Knowledge and docs
+
+Docs are written so an agent needs little context: read only what the task touches.
+
+| File | Limit | Changes |
+|---|---|---|
+| `CLAUDE.md` | 40 lines | rarely |
+| `docs/spec.md` | 120 lines | when scope or architecture changes |
+| `docs/roadmap.md` | 80 lines | every milestone |
+| `docs/decisions/NNN-*.md` | 40 lines | never after acceptance; supersede with a new ADR |
+| `docs/frisko/<topic>.md` | 120 lines | when knowledge is verified |
+| `<package>/CLAUDE.md` | 30 lines | rules of that layer |
+| `research/<source>/` | none | raw vendor material, kept as found; read only on demand |
+
+- Limits are checked by `scripts/check.sh`.
+- No status, audit or log documents: the state is git history and the roadmap.
+- Closing a milestone compresses it to one line in the roadmap and removes its working notes.
+- English everywhere; the UI is Polish.
+
+## Configuration, secrets, releases
+
+- No secrets in git. Production config lives on the Pi and next to the Kraków stacks, outside
+  the images.
+- Release only from `master` with `scripts/release.sh vMAJOR.MINOR.PATCH`: it tags master and
+  CI publishes the three images. On the Pi `./update.sh <version>` goes back if it is unhealthy.
+- After an update, watch the journal and Grafana for at least one polling cycle.

README.md

@@ -1,2 +1,25 @@
 # home-pump
 
+Heat pump (Frisko RX910-SE21) and home energy for the house in Krosno, from a phone.
+
+- What we build: [docs/spec.md](docs/spec.md)
+- Plan and current milestone: [docs/roadmap.md](docs/roadmap.md)
+- Rules for changes: [CONTRIBUTING.md](CONTRIBUTING.md)
+- Controller knowledge: [docs/frisko/](docs/frisko/rx910-se21.md)
+
+| Part | Runs | Readme |
+|---|---|---|
+| `gateway/` | Pi in Krosno, Docker: devices to InfluxDB, `/commands` | [gateway/README.md](gateway/README.md) |
+| `backend/` | Kraków, Docker: phone API | [backend/README.md](backend/README.md) |
+| `frontend/` | Kraków, Docker: web UI with nginx | [frontend/README.md](frontend/README.md) |
+
+Each part has its `Dockerfile` and `compose.yaml` (ADR-010).
+
+```bash
+scripts/check.sh                       # docs, secret scan, build and tests of all three parts
+git config core.hooksPath .githooks    # once per clone: check before every push
+scripts/release.sh vMAJOR.MINOR.PATCH  # tag master; CI publishes the three images in Gitea
+```
+
+After a release: on the Pi `./update.sh <version>` (gateway/README.md); in Kraków Arcane runs the
+backend and frontend images.

backend/.dockerignore

@@ -0,0 +1 @@
+target

backend/Dockerfile

@@ -0,0 +1,22 @@
+# Built on the build machine's own platform; the image only holds the jar and a JRE.
+FROM --platform=$BUILDPLATFORM maven:3.9-eclipse-temurin-21 AS build
+WORKDIR /src
+COPY pom.xml .
+RUN mvn -B -q dependency:go-offline
+COPY src src
+# Tests run in scripts/check.sh; some read contract files from gateway/, outside this context.
+RUN mvn -B -q package -Dmaven.test.skip=true
+
+FROM eclipse-temurin:21-jre-alpine
+# The release tag, shown in /api/health; the release workflow passes it.
+ARG VERSION=dev
+ENV VERSION=$VERSION
+USER 10001:10001
+WORKDIR /app
+COPY --from=build /src/target/home-pump-backend-1.0.0.jar app.jar
+EXPOSE 8080
+# /api/live needs no session and does not look at the gateway, so it only tells whether the backend
+# itself serves requests. busybox wget ships with alpine.
+HEALTHCHECK --interval=30s --timeout=3s --start-period=10s \
+    CMD wget -q -O /dev/null "http://127.0.0.1:${PORT:-8080}/api/live" || exit 1
+ENTRYPOINT ["java", "-jar", "app.jar"]

backend/README.md

@@ -0,0 +1,157 @@
+# Backend
+
+The phone API in Kraków (ADR-008): live state from the gateway, history from InfluxDB, setpoint
+changes passed to the gateway. JSON under `/api/` only; the web UI is the frontend's (ADR-010).
+The records in `home.backend.domain` and the examples in `src/test/resources/api/` are the contract.
+`GET /api/energy` (example `src/test/resources/api/energy.json`) is the house electricity now. `housePowerW` is the whole house by balance, because the Deye `load` registers cover only its backup output (`backupOutputW`): Deye PV1 + PV2 + Fronius PV + Deye battery (+discharge, − charge) + grid, the grid being the house meter's `total_power_active` when live, else the Deye `grid_power_w`; floored at 0, null when any of these readings is missing or stale. `today.houseKwh` is Deye PV + Fronius day energy + grid bought − grid sold + battery discharged − battery charged (Deye day counters), null when any is missing.
+`GET /api/energy/details` lists the Deye, Fronius and house meter values in labelled groups (a stale device has none); the label, unit and place of every field are the catalog in `EnergyDetailsService`: a new field is one line there.
+`GET /api/pi-sensor` is the BME280 sensor on the Raspberry Pi (the living room), example `src/test/resources/api/pi-sensor.json`:
+`time`, `stale`, `temperature` (°C), `humidity` (%), `pressure` (hPa). When it is stale (device down, no reading or older than 10 min)
+the three values are null (`pi-sensor-stale.json`).
+
+`GET /api/stats?range=7d|30d` (example `src/test/resources/api/stats.json`; 400 otherwise, 502 when InfluxDB is down) is the heat pump per local
+day (Europe/Warsaw, today included) from the raw `heat_pump` polls: `days[]` with `date`, `compressorHours`, `compressorStarts`, `cwuHours`, `coHours`,
+`avgOutdoorTemp`, `minCwuTemp`, `maxCwuTemp` (all null on a day without polls) and `totals` over the range. A poll holds its outputs
+until the next one, at most 600 s, so gaps add no hours; a start is a poll above 0 after a poll at 0, so the 300 s polling misses short cycles.
+
+`GET /api/program?days=14` (7 to 30, default 14; 400 otherwise, 502 when InfluxDB is down; example `src/test/resources/api/program.json`) is the weekly
+program as the history shows it, not read from the controller: `weekdays[]` from Monday (`day` 1) to Sunday, each with `cwu` and `room`:
+`comfort` (intervals `from`/`to`, local "HH:MM", "24:00" at midnight), `observedDays`, `agreeingDays` and `confidence` (`confirmed`: at least
+two days of that weekday agree within 5 minutes, `seen_once`, `no_data`). A boundary is the middle between the two polls where the period
+changes (`Periods`), rounded to 5 minutes; an override, ambiguous setpoints (e.g. during our writes) or a gap over 600 s drop the interval.
+Today is left out. `/api/heat-pump` has `periods` (`cwu`, `room`: `comfort`, `economy`, `unknown`, `override`; `program`, `programText`).
+
+`GET /api/battery` is the Deye battery, example `src/test/resources/api/battery.json`: live `socPct`, `powerW` (+ discharge / − charge), `voltageV`,
+`currentA`, `temperatureC`, `today` and `total` energy (`chargeKwh`, `dischargeKwh`), null when the Deye is stale (older than 10 min or down).
+The settings come from the gateway's slower `deye_settings` reading and are stale after 30 min (`battery-settings-stale.json`):
+`mode` (`touEnabled` with a Polish sentence), `schedule` (six slots, each from its start to the next one, the last wraps past midnight),
+`limits`, and `capacityKwh` = capacity in Ah x a nominal 51.2 V, since the inverter reports Ah only. When stale they are null (`schedule` empty).
+
+`/api/battery` also has `reserve` (`pct`, `floorPct`: the backup reserve of the app and the lowest the user may set) and `editable`:
+true when the gateway answers its `/battery/reserve`, i.e. it has battery commands on and `GATEWAY_TOKEN` is right; else `reserve` is null
+and `editable` false. `POST /api/battery/schedule` (examples `battery-schedule-request.json`, `battery-failed.json`) takes
+`{"enabled"?, "slots": [{"slot": 1-6, "from"?: "HH:MM", "socPct"?, "gridCharge"?}]}` and `POST /api/battery/reserve` takes `{"pct": 60}`.
+Same Origin, header and JSON rules as the other writes; the signed-in user goes on as the requester. The gateway's verdict comes back as
+`{status, message, read}`: 200 applied, 422 rejected, 409 settings unknown or changed meanwhile, 429 too soon, 502 failed (`read` is what the
+inverter holds), 400 bad body, 503 gateway unreachable or without battery commands (ADR-013).
+
+`GET /api/audit?range=7d` (`24h`, `7d` default, `30d`; 400 otherwise, 502 when InfluxDB fails) is the change history, example
+`src/test/resources/api/audit.json`: the gateway's audit rows of the heat pump (`Dom_Pompa.setpoint_audit`) and the battery
+(`electricity.deye_settings_audit`), read only, as `entries` newest first: `time`, `source` (`heat_pump`, `battery`), `what` (Polish label;
+the Deye registers are named in `DeyeSettingLabels`), `oldValue`/`newValue` (whole numbers, null when not recorded), `unit` (`°C`, `%`,
+`HHMM`, `0/1`), `who` (the signed-in user; a restore is "automatycznie (przywrócenie)") and `status` (the gateway's: APPLIED, FAILED, REJECTED, CONFLICT, INVALID).
+
+`GET /api/weather` (example `src/test/resources/api/weather.json`) is the forecast of Open-Meteo for the house and the IMGW warnings that name
+Krosno (TERYT 1862 or the powiat 1807): `today`, `tomorrow`, `dayAfter` (`date`, `weatherCode` WMO, Polish `description`, `tMax`, `tMin`,
+`precipitationMm`, `sunshineHours`, `pvForecastKwh`), `now.temperature`, `warnings` (`event`, `level` 1-3, `from`, `to`, `text`; the ones that
+ended are dropped). `pvFactor` is kWh per MJ/m^2: the Deye plus Fronius energy of the past 14 complete days (from InfluxDB, daily maximum of
+`pv_today_kwh` and `energy_day_wh`) over the forecast radiation of the same days, so no tilt or azimuth is needed; `pvForecastKwh` is the factor
+times the day's radiation, and both are null with fewer than 5 days that have both values. The forecast is kept 30 min and the warnings 10 min;
+when a refresh fails the older answer is served with `stale` true. 503 only when there never was a forecast. The sources are public and need no key.
+
+Settings are environment variables (`.env` next to `compose.yaml`); the backend refuses to start
+without the two URLs.
+Setpoint changes go only to the gateway; the signed-in user is sent as `X-Requested-By`.
+
+| Variable | Default | Meaning |
+|---|---|---|
+| `GATEWAY_URL` | required | the gateway on the Pi, e.g. `http://10.0.0.2:8080` |
+| `INFLUX_URL` | required | InfluxDB 1.x, e.g. `https://influxdb.example` |
+| `PORT` | `8080` | listening port |
+| `GATEWAY_TIMEOUT` | `5` | seconds |
+| `INFLUX_TIMEOUT` | `10` | seconds |
+| `GATEWAY_TOKEN` | unset | shared token for the gateway's `/commands`; without it the backend runs but `/api/setpoints` and `/api/presets/{id}` answer 503 |
+| `WEATHER_LAT`, `WEATHER_LON` | `49.684`, `21.770` | where the house is (Krosno, ul. Szczepańcowa), for the forecast |
+| `WEATHER_TERYT` | `1862,1807` | comma-separated TERYT powiat codes whose IMGW warnings count |
+| `USERS_FILE` | unset | local accounts, see Sign-in; outside the image like `PRESETS_FILE` |
+| `OIDC_ISSUER` | unset | Keycloak realm URL, e.g. `https://login.mariuszpacek.pl/realms/home`; unset turns OIDC off |
+| `OIDC_CLIENT_ID`, `OIDC_CLIENT_SECRET`, `OIDC_REDIRECT_URI` | required with `OIDC_ISSUER` | the confidential client; redirect `https://pompa.mariuszpacek.pl/api/auth/oidc/callback` |
+| `OIDC_REQUIRED_ROLE` | unset | a role the user must have: realm role (`realm_access.roles`) or role of this client (`resource_access.<client>.roles`) in the ID token |
+| `SESSION_SECRET` | required with `USERS_FILE` or `OIDC_ISSUER` | at least 32 bytes signing the cookies, e.g. `openssl rand -base64 48`; changing it signs everyone out |
+| `SESSION_DAYS` | `30` | how long a session lasts |
+| `TRUSTED_PROXY_HOPS` | `1` | proxies that append to `X-Forwarded-For` before the backend (Traefik: 1), for the login throttle |
+| `AUTH_DISABLED` | unset | `true` runs without sign-in (every request is `phone`), for development; refused together with `USERS_FILE` or `OIDC_ISSUER` |
+| `PRESETS_FILE` | built-in | JSON file replacing the presets: `[{"id", "name", "changes": [{"setpoint", "value", "hours"}]}]`, `hours` null means until changed; a bad file stops the start. A preset may also have `"until": "chosen"` (then no `hours`): the user picks the end, see below |
+
+```bash
+mvn -f backend/pom.xml clean package
+GATEWAY_URL=http://10.0.0.2:8080 INFLUX_URL=https://influxdb.example AUTH_DISABLED=true \
+  java -jar backend/target/home-pump-backend-1.0.0.jar        # API at http://localhost:8080/api/
+docker compose -f backend/compose.yaml up --build              # with backend/.env; network home-pump
+```
+
+## Sign-in (ADR-014)
+
+Without `USERS_FILE` or `OIDC_ISSUER` the backend refuses to start unless `AUTH_DISABLED=true`. The two ways in are
+independent: local accounts keep working when Keycloak is down, and the backend never waits for Keycloak at start
+(discovery and keys are fetched at the first sign-in and kept an hour). Every endpoint but those below answers
+`401 {"error":"unauthenticated"}` without a valid session; the writes keep their Origin, header and JSON rules.
+
+| Endpoint | Answer |
+|---|---|
+| `GET /api/auth/config` | `{"local", "oidc", "setup"}` booleans (`auth-config.json`); `setup` is true while `USERS_FILE` has no account |
+| `POST /api/auth/setup` `{"username","password"}` | first account, once: 200 `{"user","method":"local"}` and the cookie; 409 `{"error":"setup_done"}` once any account exists; 400 `weak_password` (under 10 characters) or `invalid_username`; 404 without `USERS_FILE` |
+| `GET /api/auth/users` | session needed: `[{"username"}]` |
+| `POST /api/auth/users` `{"username","password"}` | session needed: adds a local account; 200 `{"username"}`, 409 `exists`, 400 as setup |
+| `POST /api/auth/password` `{"current","new"}` | session needed, local sessions only (403 `local_only` otherwise): 204; 401 `invalid` (counts toward the throttle), 429, 400 `weak_password` |
+| `POST /api/auth/users/{name}/delete` | session needed: 204 (removing yourself also clears your cookie); 404 `unknown_user`; 409 `last_user` |
+| `POST /api/auth/login` `{"username","password"}` | 200 `{"user","method":"local"}` and the cookie; 401 `{"error":"invalid"}`; 429 `{"error":"throttled","retryAfterSeconds"}` with `Retry-After`; 404 without `USERS_FILE` |
+| `POST /api/auth/logout` | 204, cookie cleared |
+| `GET /api/auth/me` | 200 `{"user","method"}` (`auth-me.json`; `method` is `local`, `oidc`, or `none` with `AUTH_DISABLED`) or 401 |
+| `GET /api/auth/oidc/start` | 302 to Keycloak; 404 without OIDC |
+| `GET /api/auth/oidc/callback` | 302 to `/`, or to `/#login?error=oidc_unavailable` (Keycloak down), `oidc_denied` (refused or role missing), `oidc_failed` (bad state, token or code) |
+| `GET /api/live` | 200 `ok`, for the container healthcheck and external monitors: `/api/health` needs a session now |
+
+The session is a cookie `hp_session` (HttpOnly, Secure, SameSite=Lax, Path=/) signed with HMAC-SHA256 and holding user, method,
+issue time and expiry; there is no server state, so a stolen cookie lives until it expires or the secret changes; a `local` session also ends when its account
+is removed (it is checked on every request).
+The OIDC flow is authorization code with PKCE S256, state and nonce, in a 10 minute signed cookie `hp_oidc`; the ID token is
+verified here (RS256 against the JWKS key by `kid`, `iss`, `aud` and `azp`, `exp`/`iat` with 60 s skew, `nonce`).
+The user name is `preferred_username`, else `email`, else `sub`.
+
+**Local accounts**: `USERS_FILE` is JSON `[{"username": "tata", "passwordHash": "pbkdf2-sha256$600000$<salt>$<hash>"}]`, a username of
+1 to 64 of `A-Za-z0-9_.@+-`, a bad file stops the start. The app edits the file: it rewrites it atomically (temp file in the same directory, fsync, rename, mode 600), so mount a **directory** (`./auth:/config/auth`, `USERS_FILE=/config/auth/users.json`) that uid 10001 owns: `chown 10001:10001 auth`. A missing file or one with no accounts is setup mode: the first visitor to the app creates the first account in the app (accepted risk, ADR-014: Traefik admits only the two home networks). Add, remove accounts and change a password in the app; each change is logged (who, what, never a password). A hash can still be made by hand, without echoing the password (asked twice on a terminal;
+a pipe reads one line):
+
+```bash
+docker run --rm -it git.mariuszpacek.pl/mariusz.pacek/home-pump-backend:latest hash-password
+java -jar backend/target/home-pump-backend-1.0.0.jar hash-password
+```
+
+Five login attempts in 15 minutes block that username and, separately, that client address (429, `Retry-After`; an attempt is
+counted before the password is checked, so parallel guesses cannot outrun it, and a success clears the username); a blocked
+username is refused even with the right password. At most 4 passwords are hashed at once, more get 429 at once. An unknown username costs one password hash like a wrong password.
+The address is the entry `TRUSTED_PROXY_HOPS` from the right of `X-Forwarded-For` (Traefik appends the address it saw;
+what a client put in front is ignored); without it the socket's address.
+
+**Keycloak client** in the realm of `OIDC_ISSUER`: Client authentication on (confidential), only Standard flow, PKCE method
+`S256`, valid redirect URI `https://pompa.mariuszpacek.pl/api/auth/oidc/callback`, web origin `https://pompa.mariuszpacek.pl`.
+Its secret is `OIDC_CLIENT_SECRET`. Without `OIDC_REQUIRED_ROLE`, every user of the realm can sign in; the backend logs a warning at start. For `OIDC_REQUIRED_ROLE`, the client scope `roles` must put the roles into the ID token
+(its realm and client role mappers: "Add to ID token" on).
+
+`POST /api/presets/{id}` takes no body for an ordinary preset. A preset with `"until": "chosen"` (the built-in "Wyjazd")
+needs `{"until": "2026-11-02T18:00:00+01:00"}` (ISO-8601 with offset, example `src/test/resources/api/preset-away-request.json`):
+400 when it is missing, invalid, or sent to a preset that has none. Any preset also takes optional `"values"`
+(example `preset-away-values-request.json`): a whole number per setpoint of that preset, replacing the preset's value;
+the others keep it. 400 for a setpoint the preset does not change or a value outside the gateway's min, max and step
+(from `/commands`), checked before anything is sent. A timed preset (built-in "Ciepła woda teraz") also takes optional
+`"hours"` (example `preset-cwu-now-request.json`): a whole number from 1 to 4 replacing its duration; anything else, or
+hours for a held preset, is 400 `{"error":"invalid_hours"}`. A held value that is not below the current one is 422. The gateway holds those changes until then without
+renewals (ADR-012) and rejects an end that is past or over 30 days away, or a change that does not lower the value (422).
+
+`POST /api/refresh` (same Origin, header and JSON rules; send `{}`) is the "Odśwież" button: it asks the gateway for one
+extra poll of every device and passes its answer through, example `src/test/resources/api/refresh.json`
+(`requested`, and `skipped` with `retryInSeconds` for devices polled within the last minute). Read-only; 503 when
+`GATEWAY_TOKEN` is not set or the gateway is unreachable.
+
+`POST /api/setpoints/{name}/restore` (same Origin, header and JSON rules as the other writes; send `{}`) ends the
+pending change of that setpoint now and answers with the gateway's verdict, example
+`src/test/resources/api/setpoint-restored.json`: 200 restored, 404 nothing pending, 409 the value was changed
+meanwhile (left alone, the restore is dropped), 429 too soon after the last write, 502 failed (the restore stays
+pending), 503 gateway unreachable.
+
+Publish no host port in production: only the frontend, behind Traefik, may reach the backend, so Traefik's
+access rules (ADR-009) stay in front of the sign-in.
+
+`/api/health` also carries `backendVersion` (the `VERSION` the image was built with, `dev` locally) and
+`gatewayVersion` (from the gateway's `/health`; null when it is unreachable or too old to report it).

backend/compose.yaml

@@ -0,0 +1,23 @@
+# The backend in Kraków: the API only (ADR-010), reached by the frontend on the network home-pump
+# and published on no host port (ADR-009). Settings in .env next to this file (README).
+name: home-pump-backend
+services:
+  backend:
+    image: git.mariuszpacek.pl/mariusz.pacek/home-pump-backend:${VERSION:-latest}
+    build: .
+    restart: unless-stopped
+    env_file: .env
+    environment:
+      TZ: Europe/Warsaw
+    # Sign-in (README): the accounts directory, writable by uid 10001 (chown 10001:10001 auth); the app rewrites users.json in it. In .env, for example:
+    #   USERS_FILE=/config/auth/users.json         SESSION_SECRET=<openssl rand -base64 48>
+    #   OIDC_ISSUER=https://login.mariuszpacek.pl/realms/home   OIDC_CLIENT_ID=home-pump
+    #   OIDC_CLIENT_SECRET=<from Keycloak>    OIDC_REQUIRED_ROLE=family
+    #   OIDC_REDIRECT_URI=https://pompa.mariuszpacek.pl/api/auth/oidc/callback
+    volumes:
+      - ./auth:/config/auth
+    networks: [home-pump]
+
+networks:
+  home-pump:
+    name: home-pump

backend/pom.xml

@@ -0,0 +1,84 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <groupId>com.home</groupId>
+    <artifactId>home-pump-backend</artifactId>
+    <version>1.0.0</version>
+
+    <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <maven.compiler.release>21</maven.compiler.release>
+        <jackson.version>2.20.1</jackson.version>
+    </properties>
+
+    <dependencies>
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-databind</artifactId>
+            <version>${jackson.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.fasterxml.jackson.datatype</groupId>
+            <artifactId>jackson-datatype-jsr310</artifactId>
+            <version>${jackson.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.slf4j</groupId>
+            <artifactId>slf4j-simple</artifactId>
+            <version>1.7.32</version>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter</artifactId>
+            <version>5.10.0</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-junit-jupiter</artifactId>
+            <version>5.8.0</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>3.13.0</version>
+            </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-surefire-plugin</artifactId>
+                <version>3.1.2</version>
+                <configuration>
+                    <redirectTestOutputToFile>true</redirectTestOutputToFile>
+                </configuration>
+            </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-shade-plugin</artifactId>
+                <version>3.4.1</version>
+                <executions>
+                    <execution>
+                        <phase>package</phase>
+                        <goals>
+                            <goal>shade</goal>
+                        </goals>
+                        <configuration>
+                            <createDependencyReducedPom>false</createDependencyReducedPom>
+                            <transformers>
+                                <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
+                                    <mainClass>home.backend.Main</mainClass>
+                                </transformer>
+                            </transformers>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
+        </plugins>
+    </build>
+</project>

backend/src/main/java/home/backend/Backend.java

@@ -0,0 +1,85 @@
+package home.backend;
+
+import home.backend.adapters.auth.Authentication;
+import home.backend.adapters.config.PresetFile;
+import home.backend.adapters.gateway.GatewayHttpClient;
+import home.backend.adapters.gateway.GatewayHttpCommands;
+import home.backend.adapters.http.ApiServer;
+import home.backend.adapters.influx.InfluxAuditRepository;
+import home.backend.adapters.influx.InfluxHistoryRepository;
+import home.backend.adapters.influx.InfluxPvEnergy;
+import home.backend.adapters.influx.InfluxSettings;
+import home.backend.adapters.weather.ImgwClient;
+import home.backend.adapters.weather.OpenMeteoClient;
+import home.backend.adapters.weather.WeatherSettings;
+import home.backend.application.AuditService;
+import home.backend.application.BatteryService;
+import home.backend.application.EnergyDetailsService;
+import home.backend.application.EnergyService;
+import home.backend.application.HealthService;
+import home.backend.application.HeatPumpService;
+import home.backend.application.HistoryService;
+import home.backend.application.ProgramService;
+import home.backend.application.StatsService;
+import home.backend.application.LeaseRenewer;
+import home.backend.application.PiSensorService;
+import home.backend.application.SetpointService;
+import home.backend.application.WeatherService;
+
+import java.io.IOException;
+import java.net.URI;
+import java.time.Clock;
+import java.time.Duration;
+import java.util.Objects;
+
+/** Wires the adapters and services together; the only place that knows all of them. */
+final class Backend {
+
+    private static final Duration WEATHER_TIMEOUT = Duration.ofSeconds(10);
+    /** Warnings are optional, so a slow IMGW must not hold the forecast. */
+    private static final Duration WARNINGS_TIMEOUT = Duration.ofSeconds(3);
+
+    private Backend() {
+    }
+
+    /**
+     * Binds the port but does not start serving.
+     *
+     * @throws IllegalArgumentException when PRESETS_FILE or USERS_FILE is unusable
+     */
+    static ApiServer assemble(Settings settings, Clock clock) throws IOException {
+        var gateway = new GatewayHttpClient(settings.gatewayUrl(), settings.gatewayTimeout());
+        var influxSettings = new InfluxSettings(settings.influxUrl(), settings.influxTimeout());
+        var influx = new InfluxHistoryRepository(influxSettings);
+        var commands = commands(settings);
+        var setpoints = new SetpointService(commands, PresetFile.load(settings.presetsFile()));
+        return new ApiServer(settings.port(),
+                new HeatPumpService(gateway, clock),
+                new EnergyService(gateway, clock),
+                new EnergyDetailsService(gateway, clock),
+                new HealthService(gateway, clock, Objects.requireNonNullElse(System.getenv("VERSION"), "dev")),
+                new HistoryService(influx, clock), setpoints, new PiSensorService(gateway, clock),
+                new BatteryService(gateway, commands, clock),
+                new AuditService(new InfluxAuditRepository(influxSettings), clock), new StatsService(influx, clock),
+                new ProgramService(influx, clock),
+                weather(influxSettings, clock), commands,
+                Authentication.create(settings.auth(), clock));
+    }
+
+    private static WeatherService weather(InfluxSettings influx, Clock clock) {
+        var place = WeatherSettings.fromEnvironment(System.getenv());
+        return new WeatherService(
+                new OpenMeteoClient(URI.create("https://api.open-meteo.com"), place, WEATHER_TIMEOUT),
+                new ImgwClient(URI.create("https://danepubliczne.imgw.pl"), place, WARNINGS_TIMEOUT),
+                new InfluxPvEnergy(influx), clock);
+    }
+
+    /** Keeps the gateway from restoring our setpoint changes while we are up (ADR-011). */
+    static LeaseRenewer leaseRenewer(Settings settings) {
+        return new LeaseRenewer(commands(settings));
+    }
+
+    private static GatewayHttpCommands commands(Settings settings) {
+        return new GatewayHttpCommands(settings.gatewayUrl(), settings.gatewayToken(), settings.gatewayTimeout());
+    }
+}

backend/src/main/java/home/backend/Main.java

@@ -0,0 +1,41 @@
+package home.backend;
+
+import home.backend.adapters.http.ApiServer;
+
+import home.backend.adapters.auth.PasswordHashCli;
+
+import java.io.IOException;
+import java.time.Clock;
+
+public final class Main {
+
+    private Main() {
+    }
+
+    public static void main(String[] args) throws IOException {
+        if (args.length == 1 && args[0].equals("hash-password")) {
+            System.exit(PasswordHashCli.run(System.console(), System.in, System.out, System.err));
+        }
+        Settings settings;
+        ApiServer server;
+        try {
+            settings = Settings.fromEnvironment(System.getenv());
+            server = Backend.assemble(settings, Clock.systemUTC());
+        } catch (IllegalArgumentException e) {
+            System.err.println("home-pump-backend: " + e.getMessage());
+            System.exit(2);
+            return;
+        }
+        settings.auth().warnings().forEach(w -> System.err.println("home-pump-backend: WARNING: " + w));
+        Runtime.getRuntime().addShutdownHook(new Thread(server::stop));
+        if (settings.gatewayToken() == null) {
+            System.err.println("home-pump-backend: GATEWAY_TOKEN is not set, setpoint changes are disabled");
+        } else {
+            var renewer = Backend.leaseRenewer(settings);
+            Runtime.getRuntime().addShutdownHook(new Thread(renewer::close));
+            renewer.start();
+        }
+        server.start();
+        System.out.println("home-pump-backend listening on port " + server.port());
+    }
+}

backend/src/main/java/home/backend/Settings.java

@@ -0,0 +1,106 @@
+package home.backend;
+
+import home.backend.adapters.auth.AuthSettings;
+import home.backend.adapters.auth.OidcSettings;
+
+import java.net.URI;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Path;
+import java.time.Duration;
+import java.util.Map;
+import java.util.Optional;
+
+/** Twelve-factor settings: everything comes from environment variables. */
+public record Settings(URI gatewayUrl, URI influxUrl, int port, Duration gatewayTimeout, Duration influxTimeout,
+        String gatewayToken, Path presetsFile, AuthSettings auth) {
+
+    public static Settings fromEnvironment(Map<String, String> env) {
+        return new Settings(
+                url(env, "GATEWAY_URL"),
+                url(env, "INFLUX_URL"),
+                (int) number(env, "PORT", 8080, 0, 65535),
+                Duration.ofSeconds(number(env, "GATEWAY_TIMEOUT", 5, 1, 300)),
+                Duration.ofSeconds(number(env, "INFLUX_TIMEOUT", 10, 1, 300)),
+                optional(env, "GATEWAY_TOKEN"),
+                Optional.ofNullable(optional(env, "PRESETS_FILE")).map(Path::of).orElse(null),
+                auth(env));
+    }
+
+    private static final int MIN_SECRET_BYTES = 32;
+
+    /** Refuses to start open by accident: sign-in is configured, or AUTH_DISABLED=true says it is meant. */
+    private static AuthSettings auth(Map<String, String> env) {
+        Path usersFile = Optional.ofNullable(optional(env, "USERS_FILE")).map(Path::of).orElse(null);
+        OidcSettings oidc = optional(env, "OIDC_ISSUER") == null ? null : oidc(env);
+        String secret = optional(env, "SESSION_SECRET");
+        boolean disabled = "true".equals(optional(env, "AUTH_DISABLED"));
+        int days = (int) number(env, "SESSION_DAYS", 30, 1, 365);
+        int hops = (int) number(env, "TRUSTED_PROXY_HOPS", 1, 1, 10);
+        boolean configured = usersFile != null || oidc != null;
+        if (disabled && configured) {
+            throw new IllegalArgumentException("AUTH_DISABLED=true contradicts USERS_FILE and OIDC_ISSUER: unset one");
+        }
+        if (!disabled && !configured) {
+            throw new IllegalArgumentException("no sign-in configured: set USERS_FILE and/or OIDC_ISSUER, "
+                    + "or AUTH_DISABLED=true for development only");
+        }
+        if (configured && (secret == null || secret.getBytes(StandardCharsets.UTF_8).length < MIN_SECRET_BYTES)) {
+            throw new IllegalArgumentException("SESSION_SECRET is required and must be at least " + MIN_SECRET_BYTES
+                    + " bytes, e.g. from: openssl rand -base64 48");
+        }
+        return new AuthSettings(usersFile, oidc, secret, days, disabled, hops);
+    }
+
+    private static OidcSettings oidc(Map<String, String> env) {
+        for (String name : new String[] {"OIDC_CLIENT_ID", "OIDC_CLIENT_SECRET", "OIDC_REDIRECT_URI"}) {
+            if (optional(env, name) == null) {
+                throw new IllegalArgumentException(name + " is required when OIDC_ISSUER is set");
+            }
+        }
+        return new OidcSettings(URI.create(optional(env, "OIDC_ISSUER")), optional(env, "OIDC_CLIENT_ID"),
+                optional(env, "OIDC_CLIENT_SECRET"), URI.create(optional(env, "OIDC_REDIRECT_URI")),
+                optional(env, "OIDC_REQUIRED_ROLE"));
+    }
+
+    /** Null when unset or blank. */
+    private static String optional(Map<String, String> env, String name) {
+        String value = env.get(name);
+        return value == null || value.isBlank() ? null : value.strip();
+    }
+
+    private static URI url(Map<String, String> env, String name) {
+        String value = env.get(name);
+        if (value == null || value.isBlank()) {
+            throw new IllegalArgumentException(name + " is required, e.g. " + name + "=http://host:8080");
+        }
+        URI uri = URI.create(value.strip());
+        if (uri.getHost() == null || !("http".equals(uri.getScheme()) || "https".equals(uri.getScheme()))) {
+            throw new IllegalArgumentException(name + " must be an http(s) URL with a host, got: " + value);
+        }
+        // The clients append their own paths to this base; a path here would be silently dropped or doubled.
+        boolean hasPath = !uri.getRawPath().isEmpty() && !uri.getRawPath().equals("/");
+        if (hasPath || uri.getRawQuery() != null || uri.getRawFragment() != null) {
+            throw new IllegalArgumentException(name + " must be only scheme, host and port, without a path, got: "
+                    + value);
+        }
+        return uri;
+    }
+
+    /** Timeouts are whole seconds. */
+    private static long number(Map<String, String> env, String name, long fallback, long min, long max) {
+        String value = env.get(name);
+        if (value == null || value.isBlank()) {
+            return fallback;
+        }
+        try {
+            long number = Long.parseLong(value.strip());
+            if (number >= min && number <= max) {
+                return number;
+            }
+        } catch (NumberFormatException e) {
+            // reported below with the same message
+        }
+        throw new IllegalArgumentException(name + " must be a whole number from " + min + " to " + max
+                + ", got: " + value);
+    }
+}

backend/src/main/java/home/backend/adapters/auth/AuthSettings.java

@@ -0,0 +1,20 @@
+package home.backend.adapters.auth;
+
+import java.nio.file.Path;
+import java.util.List;
+
+/**
+ * How users sign in. At least one of usersFile and oidc, or disabled; the secret signs the cookies.
+ * proxyHops is how many proxies append to X-Forwarded-For before the backend (Traefik: 1).
+ */
+public record AuthSettings(Path usersFile, OidcSettings oidc, String sessionSecret, int sessionDays,
+        boolean disabled, int proxyHops) {
+
+    /** Things worth saying at startup. */
+    public List<String> warnings() {
+        if (oidc != null && oidc.requiredRole() == null) {
+            return List.of("OIDC_REQUIRED_ROLE is not set: every user of the Keycloak realm can sign in");
+        }
+        return List.of();
+    }
+}

backend/src/main/java/home/backend/adapters/auth/Authentication.java

@@ -0,0 +1,166 @@
+package home.backend.adapters.auth;
+
+import java.nio.charset.StandardCharsets;
+import java.time.Clock;
+import java.time.Duration;
+import java.util.Locale;
+import java.util.Optional;
+import java.util.concurrent.Semaphore;
+
+/** Who may use the API: local accounts and OIDC, independent of each other, both ending in a session cookie. */
+public final class Authentication {
+
+    public static final String LOCAL = "local";
+
+    public enum Status { OK, INVALID, THROTTLED }
+
+    public record Login(Status status, long retryAfterSeconds) {
+    }
+
+    private static final int MAX_FAILURES = 5;
+    private static final Duration THROTTLE_WINDOW = Duration.ofMinutes(15);
+    /** Password hashing is slow on purpose; a flood must not queue up behind it. */
+    private static final int PARALLEL_HASHES = 4;
+    private static final int MIN_PASSWORD = 10;
+    private static final long BUSY_RETRY_SECONDS = 1;
+
+    private final Sessions sessions;
+    private final UserStore users;
+    private final LoginThrottle throttle;
+    private final OidcFlow oidc;
+    private final int proxyHops;
+    private final Semaphore hashing = new Semaphore(PARALLEL_HASHES);
+
+    private Authentication(Sessions sessions, UserStore users, LoginThrottle throttle, OidcFlow oidc, int proxyHops) {
+        this.sessions = sessions;
+        this.users = users;
+        this.throttle = throttle;
+        this.oidc = oidc;
+        this.proxyHops = proxyHops;
+    }
+
+    /** @throws IllegalArgumentException when USERS_FILE is unusable */
+    public static Authentication create(AuthSettings settings, Clock clock) {
+        if (settings.disabled()) {
+            return new Authentication(null, null, null, null, settings.proxyHops());
+        }
+        var tokens = new SignedTokens(settings.sessionSecret().getBytes(StandardCharsets.UTF_8), clock);
+        return new Authentication(new Sessions(tokens, clock, Duration.ofDays(settings.sessionDays())),
+                settings.usersFile() == null ? null : UserStore.load(settings.usersFile()),
+                new LoginThrottle(clock, MAX_FAILURES, THROTTLE_WINDOW),
+                settings.oidc() == null ? null : new OidcFlow(settings.oidc(), tokens, clock),
+                settings.proxyHops());
+    }
+
+    /** For development and tests: every request is the user "phone". */
+    public static Authentication disabled() {
+        return new Authentication(null, null, null, null, 1);
+    }
+
+    public boolean localEnabled() {
+        return users != null;
+    }
+
+    public boolean oidcEnabled() {
+        return oidc != null;
+    }
+
+    public OidcFlow oidc() {
+        return oidc;
+    }
+
+    public int proxyHops() {
+        return proxyHops;
+    }
+
+    public Optional<Session> session(String cookieHeader) {
+        if (sessions == null) {
+            return Optional.of(Session.OPEN);
+        }
+        // A removed account loses its sessions at once; OIDC sessions end with their expiry.
+        return sessions.read(cookieHeader).filter(s -> !LOCAL.equals(s.method()) || users != null && users.exists(s.user()));
+    }
+
+    /** Checks the password unless the user or the address is blocked; a blocked one learns nothing about it. */
+    public Login login(String username, char[] password, String clientIp) {
+        String userKey = "user:" + username.toLowerCase(Locale.ROOT);
+        String ipKey = "ip:" + clientIp;
+        long wait = throttle.tryAcquire(userKey, ipKey);
+        if (wait > 0) {
+            return new Login(Status.THROTTLED, wait);
+        }
+        if (!hashing.tryAcquire()) {
+            throttle.release(userKey, ipKey);
+            return new Login(Status.THROTTLED, BUSY_RETRY_SECONDS);
+        }
+        try {
+            if (users.authenticate(username, password)) {
+                throttle.cleared(userKey);
+                throttle.release(ipKey);
+                return new Login(Status.OK, 0);
+            }
+            return new Login(Status.INVALID, 0);
+        } finally {
+            hashing.release();
+        }
+    }
+
+    public boolean setupNeeded() {
+        return users != null && users.isEmpty();
+    }
+
+    public static boolean strongEnough(String password) {
+        return password.length() >= MIN_PASSWORD;
+    }
+
+    /** Creates the first account, once: OK for the winner, INVALID (setup is done) for everyone after. */
+    public Login setup(String username, char[] password, String clientIp) {
+        String ipKey = "ip:" + clientIp;
+        long wait = throttle.tryAcquire(ipKey);
+        if (wait > 0) {
+            return new Login(Status.THROTTLED, wait);
+        }
+        if (!users.addFirst(username, PasswordHash.create(password))) {
+            return new Login(Status.INVALID, 0);
+        }
+        System.err.println("home-pump-backend: setup created the first account " + username);
+        throttle.release(ipKey);
+        return new Login(Status.OK, 0);
+    }
+
+    public java.util.List<String> usernames() {
+        return users.usernames();
+    }
+
+    /** @return false when the name is taken */
+    public boolean addUser(String by, String username, char[] password) {
+        boolean added = users.add(username, PasswordHash.create(password));
+        System.err.println("home-pump-backend: " + by + " added account " + username + (added ? "" : " (refused, exists)"));
+        return added;
+    }
+
+    /** Checks the current password like a login does (throttled), then sets the new one. */
+    public Login changePassword(String username, char[] current, char[] next, String clientIp) {
+        Login login = login(username, current, clientIp);
+        if (login.status() == Status.OK) {
+            users.changePassword(username, PasswordHash.create(next));
+            System.err.println("home-pump-backend: " + username + " changed their password");
+        }
+        return login;
+    }
+
+    public UserStore.Removal removeUser(String by, String username) {
+        var removal = users.remove(username);
+        System.err.println("home-pump-backend: " + by + " removed account " + username + ": " + removal);
+        return removal;
+    }
+
+    /** The Set-Cookie header value that signs the user in. */
+    public String sessionCookie(String user, String method) {
+        return sessions.setCookie(user, method);
+    }
+
+    public String clearedSessionCookie() {
+        return sessions == null ? "" : sessions.clearCookie();
+    }
+}

backend/src/main/java/home/backend/adapters/auth/Base64Url.java

@@ -0,0 +1,18 @@
+package home.backend.adapters.auth;
+
+import java.util.Base64;
+
+/** Unpadded base64url, as tokens and PKCE use it. */
+final class Base64Url {
+
+    private Base64Url() {
+    }
+
+    static String encode(byte[] bytes) {
+        return Base64.getUrlEncoder().withoutPadding().encodeToString(bytes);
+    }
+
+    static byte[] decode(String text) {
+        return Base64.getUrlDecoder().decode(text);
+    }
+}

backend/src/main/java/home/backend/adapters/auth/Cookies.java

@@ -0,0 +1,36 @@
+package home.backend.adapters.auth;
+
+import java.time.Duration;
+import java.util.Optional;
+
+/** Reads the Cookie header and builds Set-Cookie headers with the flags every cookie here carries. */
+final class Cookies {
+
+    private Cookies() {
+    }
+
+    static Optional<String> read(String header, String name) {
+        if (header == null) {
+            return Optional.empty();
+        }
+        for (String pair : header.split(";")) {
+            String[] kv = pair.trim().split("=", 2);
+            if (kv.length == 2 && kv[0].equals(name)) {
+                return Optional.of(kv[1]);
+            }
+        }
+        return Optional.empty();
+    }
+
+    static String set(String name, String value, Duration maxAge, String path) {
+        return name + "=" + value + "; Max-Age=" + maxAge.toSeconds() + attributes(path);
+    }
+
+    static String clear(String name, String path) {
+        return name + "=; Max-Age=0" + attributes(path);
+    }
+
+    private static String attributes(String path) {
+        return "; Path=" + path + "; HttpOnly; Secure; SameSite=Lax";
+    }
+}

backend/src/main/java/home/backend/adapters/auth/IdTokenVerifier.java

@@ -0,0 +1,143 @@
+package home.backend.adapters.auth;
+
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.security.GeneralSecurityException;
+import java.security.MessageDigest;
+import java.security.PublicKey;
+import java.security.Signature;
+import java.time.Clock;
+import java.time.Duration;
+import java.util.ArrayList;
+import java.util.List;
+
+import static home.backend.adapters.auth.OidcException.Reason.DENIED;
+import static home.backend.adapters.auth.OidcException.Reason.FAILED;
+
+/** Checks an ID token with the JDK alone: RS256 signature, issuer, audience, times, nonce and the required role. */
+final class IdTokenVerifier {
+
+    /** The signing keys of the identity provider. */
+    interface Keys {
+        PublicKey key(String kid) throws OidcException;
+    }
+
+    private static final ObjectMapper JSON = new ObjectMapper();
+    private static final Duration SKEW = Duration.ofSeconds(60);
+
+    private final OidcSettings settings;
+    private final Clock clock;
+
+    IdTokenVerifier(OidcSettings settings, Clock clock) {
+        this.settings = settings;
+        this.clock = clock;
+    }
+
+    /** @return the user name of the token */
+    String verify(String idToken, String nonce, Keys keys) throws OidcException {
+        String[] parts = idToken.split("\\.", -1);
+        if (parts.length != 3) {
+            throw new OidcException(FAILED, "the ID token is not a JWT");
+        }
+        JsonNode header = json(parts[0]);
+        if (!"RS256".equals(header.path("alg").asText())) {
+            throw new OidcException(FAILED, "the ID token is not signed with RS256");
+        }
+        verifySignature(parts[0] + "." + parts[1], parts[2], keys.key(header.path("kid").asText()));
+        JsonNode claims = json(parts[1]);
+        checkClaims(claims, nonce);
+        checkRole(claims);
+        return userName(claims);
+    }
+
+    private void checkClaims(JsonNode claims, String nonce) throws OidcException {
+        long now = clock.instant().getEpochSecond();
+        if (!settings.issuerBase().equals(claims.path("iss").asText("").replaceAll("/+$", ""))) {
+            throw new OidcException(FAILED, "wrong issuer");
+        }
+        if (!audiences(claims).contains(settings.clientId())) {
+            throw new OidcException(FAILED, "the token is for another client");
+        }
+        if (audiences(claims).size() > 1 && !settings.clientId().equals(claims.path("azp").asText())) {
+            throw new OidcException(FAILED, "wrong authorized party");
+        }
+        if (!claims.path("exp").canConvertToLong() || claims.get("exp").asLong() + SKEW.toSeconds() <= now) {
+            throw new OidcException(FAILED, "the token has expired");
+        }
+        if (!claims.path("iat").canConvertToLong() || claims.get("iat").asLong() - SKEW.toSeconds() > now) {
+            throw new OidcException(FAILED, "the token is issued in the future");
+        }
+        boolean sameNonce = MessageDigest.isEqual(nonce.getBytes(StandardCharsets.UTF_8),
+                claims.path("nonce").asText("").getBytes(StandardCharsets.UTF_8));
+        if (!sameNonce) {
+            throw new OidcException(FAILED, "wrong nonce");
+        }
+    }
+
+    /** A realm role or a role of this client, as Keycloak puts them in {@code realm_access} and {@code resource_access}. */
+    private void checkRole(JsonNode claims) throws OidcException {
+        String role = settings.requiredRole();
+        if (role == null) {
+            return;
+        }
+        boolean has = contains(claims.path("realm_access").path("roles"), role)
+                || contains(claims.path("resource_access").path(settings.clientId()).path("roles"), role);
+        if (!has) {
+            throw new OidcException(DENIED, "the user lacks the role " + role);
+        }
+    }
+
+    private String userName(JsonNode claims) throws OidcException {
+        for (String claim : new String[] {"preferred_username", "email", "sub"}) {
+            String name = claims.path(claim).asText("");
+            if (Session.isValidUser(name)) {
+                return name;
+            }
+        }
+        throw new OidcException(FAILED, "the token has no usable user name");
+    }
+
+    private static List<String> audiences(JsonNode claims) {
+        JsonNode aud = claims.path("aud");
+        var all = new ArrayList<String>();
+        if (aud.isArray()) {
+            aud.forEach(a -> all.add(a.asText()));
+        } else if (aud.isTextual()) {
+            all.add(aud.asText());
+        }
+        return all;
+    }
+
+    private static boolean contains(JsonNode array, String value) {
+        for (JsonNode item : array) {
+            if (value.equals(item.asText())) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    private static void verifySignature(String signedPart, String signature, PublicKey key) throws OidcException {
+        try {
+            Signature rsa = Signature.getInstance("SHA256withRSA");
+            rsa.initVerify(key);
+            rsa.update(signedPart.getBytes(StandardCharsets.US_ASCII));
+            if (!rsa.verify(Base64Url.decode(signature))) {
+                throw new OidcException(FAILED, "the ID token signature is wrong");
+            }
+        } catch (GeneralSecurityException | IllegalArgumentException e) {
+            throw new OidcException(FAILED, "the ID token signature cannot be checked", e);
+        }
+    }
+
+    private static JsonNode json(String part) throws OidcException {
+        try {
+            return JSON.readTree(Base64Url.decode(part));
+        } catch (IOException | IllegalArgumentException e) {
+            throw new OidcException(FAILED, "the ID token is malformed", e);
+        }
+    }
+}

backend/src/main/java/home/backend/adapters/auth/LoginThrottle.java

@@ -0,0 +1,70 @@
+package home.backend.adapters.auth;
+
+import java.time.Clock;
+import java.time.Duration;
+import java.time.Instant;
+import java.util.ArrayDeque;
+import java.util.HashMap;
+import java.util.Map;
+
+/** Blocks a key (a username or a client address) after too many failures within a window. */
+public final class LoginThrottle {
+
+    private final Clock clock;
+    private final int maxFailures;
+    private final Duration window;
+    /** The newest failures of each key, at most {@code maxFailures}, oldest first. */
+    private final Map<String, ArrayDeque<Instant>> failures = new HashMap<>();
+
+    public LoginThrottle(Clock clock, int maxFailures, Duration window) {
+        this.clock = clock;
+        this.maxFailures = maxFailures;
+        this.window = window;
+    }
+
+    /**
+     * Counts an attempt against every key before the password is checked, so parallel guesses cannot
+     * outrun the limit; {@link #release} takes it back.
+     *
+     * @return 0 when the attempt may go on, else the seconds until the most blocked key may try again
+     */
+    public synchronized long tryAcquire(String... keys) {
+        Instant now = clock.instant();
+        long wait = 0;
+        for (String key : keys) {
+            var times = failures.get(key);
+            if (times != null && times.size() >= maxFailures && times.peekFirst().plus(window).isAfter(now)) {
+                wait = Math.max(wait, Duration.between(now, times.peekFirst().plus(window)).toSeconds() + 1);
+            }
+        }
+        if (wait > 0) {
+            return wait;
+        }
+        failures.values().removeIf(times -> !times.peekLast().plus(window).isAfter(now));
+        for (String key : keys) {
+            var times = failures.computeIfAbsent(key, k -> new ArrayDeque<>());
+            times.addLast(now);
+            if (times.size() > maxFailures) {
+                times.removeFirst();
+            }
+        }
+        return 0;
+    }
+
+    /** Takes back the newest attempt of each key. */
+    public synchronized void release(String... keys) {
+        for (String key : keys) {
+            var times = failures.get(key);
+            if (times != null) {
+                times.pollLast();
+                if (times.isEmpty()) {
+                    failures.remove(key);
+                }
+            }
+        }
+    }
+
+    public synchronized void cleared(String key) {
+        failures.remove(key);
+    }
+}

backend/src/main/java/home/backend/adapters/auth/OidcException.java

@@ -0,0 +1,40 @@
+package home.backend.adapters.auth;
+
+/** Why an OIDC sign-in did not happen; the code is what the login screen is told. */
+public final class OidcException extends Exception {
+
+    public enum Reason {
+        /** Keycloak did not answer. */
+        UNAVAILABLE("oidc_unavailable"),
+        /** The user said no, or lacks the required role. */
+        DENIED("oidc_denied"),
+        /** Anything else: bad state, a token that does not verify, a refused code. */
+        FAILED("oidc_failed");
+
+        private final String code;
+
+        Reason(String code) {
+            this.code = code;
+        }
+
+        public String code() {
+            return code;
+        }
+    }
+
+    private final Reason reason;
+
+    public OidcException(Reason reason, String message) {
+        super(message);
+        this.reason = reason;
+    }
+
+    public OidcException(Reason reason, String message, Throwable cause) {
+        super(message, cause);
+        this.reason = reason;
+    }
+
+    public Reason reason() {
+        return reason;
+    }
+}

backend/src/main/java/home/backend/adapters/auth/OidcFlow.java

@@ -0,0 +1,113 @@
+package home.backend.adapters.auth;
+
+import java.net.URI;
+import java.net.URLEncoder;
+import java.nio.charset.StandardCharsets;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.security.SecureRandom;
+import java.time.Clock;
+import java.time.Duration;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+import static home.backend.adapters.auth.OidcException.Reason.DENIED;
+import static home.backend.adapters.auth.OidcException.Reason.FAILED;
+
+/**
+ * Authorization code flow with PKCE (S256), state and nonce. What must survive the trip to the identity
+ * provider travels in a short-lived signed cookie, so the backend keeps no state.
+ */
+public final class OidcFlow {
+
+    /** Where to send the browser, and the cookie to set on that response. */
+    public record Start(URI location, String setCookie) {
+    }
+
+    private static final String COOKIE = "hp_oidc";
+    private static final String PURPOSE = "oidc-login";
+    private static final String PATH = "/api/auth/oidc";
+    private static final Duration LOGIN_TIME = Duration.ofMinutes(10);
+    private static final Duration TIMEOUT = Duration.ofSeconds(5);
+    private static final SecureRandom RANDOM = new SecureRandom();
+
+    private final OidcSettings settings;
+    private final OidcProvider provider;
+    private final IdTokenVerifier verifier;
+    private final SignedTokens tokens;
+
+    OidcFlow(OidcSettings settings, SignedTokens tokens, Clock clock) {
+        this.settings = settings;
+        this.provider = new OidcProvider(settings, TIMEOUT, clock);
+        this.verifier = new IdTokenVerifier(settings, clock);
+        this.tokens = tokens;
+    }
+
+    /** @throws OidcException UNAVAILABLE when the identity provider does not answer */
+    public Start start() throws OidcException {
+        String state = random();
+        String nonce = random();
+        String verifierText = random();
+        Map<String, String> query = new LinkedHashMap<>();
+        query.put("response_type", "code");
+        query.put("client_id", settings.clientId());
+        query.put("redirect_uri", settings.redirectUri().toString());
+        query.put("scope", "openid profile");
+        query.put("state", state);
+        query.put("nonce", nonce);
+        query.put("code_challenge", challenge(verifierText));
+        query.put("code_challenge_method", "S256");
+        URI endpoint = provider.endpoints().authorization();
+        String separator = endpoint.getRawQuery() == null ? "?" : "&";
+        String cookie = Cookies.set(COOKIE, tokens.issue(PURPOSE, LOGIN_TIME,
+                Map.of("state", state, "nonce", nonce, "verifier", verifierText)), LOGIN_TIME, PATH);
+        return new Start(URI.create(endpoint + separator + query.entrySet().stream()
+                .map(e -> e.getKey() + "=" + URLEncoder.encode(e.getValue(), StandardCharsets.UTF_8))
+                .collect(Collectors.joining("&"))), cookie);
+    }
+
+    /** @return the signed-in user's name */
+    public String callback(Map<String, String> query, String cookieHeader) throws OidcException {
+        Map<String, String> login = Cookies.read(cookieHeader, COOKIE).flatMap(t -> tokens.read(PURPOSE, t))
+                .orElseThrow(() -> new OidcException(FAILED, "no login in progress, or it took too long"));
+        boolean sameState = MessageDigest.isEqual(login.get("state").getBytes(StandardCharsets.UTF_8),
+                query.getOrDefault("state", "").getBytes(StandardCharsets.UTF_8));
+        if (!sameState) {
+            throw new OidcException(FAILED, "wrong state");
+        }
+        if ("access_denied".equals(query.get("error"))) {
+            throw new OidcException(DENIED, "the user denied access");
+        }
+        String code = query.get("code");
+        if (code == null || code.isEmpty()) {
+            throw new OidcException(FAILED, "the identity provider answered with " + printable(query.get("error")));
+        }
+        return verifier.verify(provider.exchange(code, login.get("verifier")), login.get("nonce"), provider);
+    }
+
+    public String clearCookie() {
+        return Cookies.clear(COOKIE, PATH);
+    }
+
+    /** The provider's text goes into the log: letters, digits and a few separators only, and short. */
+    static String printable(String text) {
+        String safe = text == null ? "nothing" : text.replaceAll("[^A-Za-z0-9_. -]", "?");
+        return safe.length() > 40 ? safe.substring(0, 40) + "..." : safe;
+    }
+
+    private static String random() {
+        byte[] bytes = new byte[32];
+        RANDOM.nextBytes(bytes);
+        return Base64Url.encode(bytes);
+    }
+
+    private static String challenge(String verifierText) {
+        try {
+            return Base64Url.encode(MessageDigest.getInstance("SHA-256")
+                    .digest(verifierText.getBytes(StandardCharsets.US_ASCII)));
+        } catch (NoSuchAlgorithmException e) {
+            throw new IllegalStateException("SHA-256 is part of every JDK", e);
+        }
+    }
+}

backend/src/main/java/home/backend/adapters/auth/OidcProvider.java

@@ -0,0 +1,179 @@
+package home.backend.adapters.auth;
+
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+import java.io.IOException;
+import java.math.BigInteger;
+import java.net.URI;
+import java.net.URLEncoder;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
+import java.nio.charset.StandardCharsets;
+import java.security.GeneralSecurityException;
+import java.security.KeyFactory;
+import java.security.PublicKey;
+import java.security.spec.RSAPublicKeySpec;
+import java.time.Clock;
+import java.time.Duration;
+import java.time.Instant;
+import java.util.Base64;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+import static home.backend.adapters.auth.OidcException.Reason.FAILED;
+import static home.backend.adapters.auth.OidcException.Reason.UNAVAILABLE;
+
+/**
+ * The identity provider over HTTP: discovery, signing keys and the code exchange. Everything is fetched on first
+ * use and kept, so an identity provider that is down never delays the start and never affects local login.
+ */
+final class OidcProvider implements IdTokenVerifier.Keys {
+
+    record Endpoints(URI authorization, URI token, URI jwks) {
+    }
+
+    private static final ObjectMapper JSON = new ObjectMapper();
+    private static final Duration CACHE = Duration.ofHours(1);
+    /** An unknown key id may mean a rotation; look again, but not on every forged token. */
+    private static final Duration REFETCH_AFTER = Duration.ofMinutes(1);
+
+    private final OidcSettings settings;
+    private final HttpClient http;
+    private final Duration timeout;
+    private final Clock clock;
+    private Endpoints endpoints;
+    private Instant endpointsAt = Instant.MIN;
+    private Map<String, PublicKey> keys = Map.of();
+    private Instant keysAt = Instant.MIN;
+
+    OidcProvider(OidcSettings settings, Duration timeout, Clock clock) {
+        this.settings = settings;
+        this.timeout = timeout;
+        this.clock = clock;
+        this.http = HttpClient.newBuilder().connectTimeout(timeout).build();
+    }
+
+    /** The network calls run outside the lock, so a hanging identity provider holds up only its own callers. */
+    Endpoints endpoints() throws OidcException {
+        synchronized (this) {
+            if (endpoints != null && !endpointsAt.plus(CACHE).isBefore(clock.instant())) {
+                return endpoints;
+            }
+        }
+        String base = settings.issuerBase();
+        JsonNode doc = getJson(URI.create(base + "/.well-known/openid-configuration"));
+        if (!base.equals(doc.path("issuer").asText("").replaceAll("/+$", ""))) {
+            throw new OidcException(FAILED, "the discovery document names another issuer");
+        }
+        var fresh = new Endpoints(uri(doc, "authorization_endpoint"), uri(doc, "token_endpoint"), uri(doc, "jwks_uri"));
+        synchronized (this) {
+            endpoints = fresh;
+            endpointsAt = clock.instant();
+        }
+        return fresh;
+    }
+
+    @Override
+    public PublicKey key(String kid) throws OidcException {
+        synchronized (this) {
+            boolean stale = keysAt.plus(CACHE).isBefore(clock.instant());
+            boolean unknownAndRefetchable = !keys.containsKey(kid)
+                    && keysAt.plus(REFETCH_AFTER).isBefore(clock.instant());
+            if (!stale && !unknownAndRefetchable) {
+                return known(kid);
+            }
+        }
+        Map<String, PublicKey> fresh = parseKeys(getJson(endpoints().jwks()));
+        synchronized (this) {
+            keys = fresh;
+            keysAt = clock.instant();
+            return known(kid);
+        }
+    }
+
+    private PublicKey known(String kid) throws OidcException {
+        PublicKey key = keys.get(kid);
+        if (key == null) {
+            throw new OidcException(FAILED, "no signing key " + kid);
+        }
+        return key;
+    }
+
+    /** @return the ID token the identity provider issued for the code */
+    String exchange(String code, String verifier) throws OidcException {
+        var form = Map.of("grant_type", "authorization_code", "code", code,
+                "redirect_uri", settings.redirectUri().toString(), "code_verifier", verifier);
+        String credentials = encode(settings.clientId()) + ":" + encode(settings.clientSecret());
+        var request = HttpRequest.newBuilder(endpoints().token()).timeout(timeout)
+                .header("Content-Type", "application/x-www-form-urlencoded")
+                .header("Authorization", "Basic " + Base64.getEncoder()
+                        .encodeToString(credentials.getBytes(StandardCharsets.UTF_8)))
+                .POST(HttpRequest.BodyPublishers.ofString(form.entrySet().stream()
+                        .map(e -> e.getKey() + "=" + encode(e.getValue())).collect(Collectors.joining("&"))))
+                .build();
+        JsonNode answer = send(request, "the token endpoint");
+        String idToken = answer.path("id_token").asText("");
+        if (idToken.isEmpty()) {
+            throw new OidcException(FAILED, "the token endpoint sent no id_token");
+        }
+        return idToken;
+    }
+
+    private JsonNode getJson(URI uri) throws OidcException {
+        return send(HttpRequest.newBuilder(uri).timeout(timeout).GET().build(), uri.getPath());
+    }
+
+    private JsonNode send(HttpRequest request, String what) throws OidcException {
+        try {
+            HttpResponse<String> response = http.send(request, HttpResponse.BodyHandlers.ofString());
+            if (response.statusCode() >= 500) {
+                throw new OidcException(UNAVAILABLE, what + " answered " + response.statusCode());
+            }
+            if (response.statusCode() != 200) {
+                throw new OidcException(FAILED, what + " answered " + response.statusCode());
+            }
+            return JSON.readTree(response.body());
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            throw new OidcException(UNAVAILABLE, what + " was interrupted", e);
+        } catch (IOException e) {
+            throw new OidcException(UNAVAILABLE, what + " is unreachable: " + e, e);
+        }
+    }
+
+    /** A key that cannot be read is skipped, so one odd entry does not lock everyone out. */
+    private static Map<String, PublicKey> parseKeys(JsonNode jwks) {
+        Map<String, PublicKey> keys = new HashMap<>();
+        for (JsonNode jwk : jwks.path("keys")) {
+            boolean signingRsa = "RSA".equals(jwk.path("kty").asText()) && !"enc".equals(jwk.path("use").asText());
+            if (signingRsa && jwk.hasNonNull("kid")) {
+                try {
+                    keys.put(jwk.get("kid").asText(), KeyFactory.getInstance("RSA").generatePublic(
+                            new RSAPublicKeySpec(integer(jwk, "n"), integer(jwk, "e"))));
+                } catch (GeneralSecurityException | IllegalArgumentException e) {
+                    System.err.println("home-pump-backend: skipping unusable signing key " + jwk.get("kid").asText());
+                }
+            }
+        }
+        return keys;
+    }
+
+    private static BigInteger integer(JsonNode jwk, String field) {
+        return new BigInteger(1, Base64Url.decode(jwk.path(field).asText()));
+    }
+
+    private static URI uri(JsonNode doc, String field) throws OidcException {
+        String value = doc.path(field).asText("");
+        if (value.isEmpty()) {
+            throw new OidcException(FAILED, "the discovery document has no " + field);
+        }
+        return URI.create(value);
+    }
+
+    private static String encode(String value) {
+        return URLEncoder.encode(value, StandardCharsets.UTF_8);
+    }
+}

backend/src/main/java/home/backend/adapters/auth/OidcSettings.java

@@ -0,0 +1,12 @@
+package home.backend.adapters.auth;
+
+import java.net.URI;
+
+/** requiredRole is null when any user of the realm may sign in. */
+public record OidcSettings(URI issuer, String clientId, String clientSecret, URI redirectUri, String requiredRole) {
+
+    /** The issuer without a trailing slash, the form tokens and discovery are compared in. */
+    String issuerBase() {
+        return issuer.toString().replaceAll("/+$", "");
+    }
+}

backend/src/main/java/home/backend/adapters/auth/PasswordHash.java

@@ -0,0 +1,78 @@
+package home.backend.adapters.auth;
+
+import javax.crypto.SecretKeyFactory;
+import javax.crypto.spec.PBEKeySpec;
+import java.security.GeneralSecurityException;
+import java.security.MessageDigest;
+import java.security.SecureRandom;
+import java.util.Base64;
+
+/** Password hashes as {@code pbkdf2-sha256$<iterations>$<salt b64>$<hash b64>}: the cost travels with the hash. */
+public final class PasswordHash {
+
+    private static final String SCHEME = "pbkdf2-sha256";
+    private static final int ITERATIONS = 600_000;
+    /** A file with a cheaper hash is refused, so a weak one cannot slip in. */
+    private static final int MIN_ITERATIONS = 310_000;
+    private static final int SALT_BYTES = 16;
+    private static final int HASH_BITS = 256;
+    private static final SecureRandom RANDOM = new SecureRandom();
+
+    private record Parsed(int iterations, byte[] salt, byte[] hash) {
+    }
+
+    private PasswordHash() {
+    }
+
+    public static String create(char[] password) {
+        byte[] salt = new byte[SALT_BYTES];
+        RANDOM.nextBytes(salt);
+        return String.join("$", SCHEME, String.valueOf(ITERATIONS), Base64.getEncoder().encodeToString(salt),
+                Base64.getEncoder().encodeToString(derive(password, salt, ITERATIONS, HASH_BITS)));
+    }
+
+    /** Compares in constant time. */
+    public static boolean matches(String stored, char[] password) {
+        Parsed parsed = parse(stored);
+        byte[] actual = derive(password, parsed.salt(), parsed.iterations(), parsed.hash().length * 8);
+        return MessageDigest.isEqual(parsed.hash(), actual);
+    }
+
+    /** @throws IllegalArgumentException when the text is not a hash this class made or accepts */
+    public static void requireValid(String stored) {
+        parse(stored);
+    }
+
+    private static Parsed parse(String stored) {
+        String[] parts = stored == null ? new String[0] : stored.split("\\$");
+        if (parts.length != 4 || !SCHEME.equals(parts[0])) {
+            throw new IllegalArgumentException("a password hash must look like " + SCHEME
+                    + "$<iterations>$<salt>$<hash>; create one with: hash-password");
+        }
+        try {
+            int iterations = Integer.parseInt(parts[1]);
+            byte[] salt = Base64.getDecoder().decode(parts[2]);
+            byte[] hash = Base64.getDecoder().decode(parts[3]);
+            if (iterations < MIN_ITERATIONS || salt.length < SALT_BYTES || hash.length < HASH_BITS / 8) {
+                throw new IllegalArgumentException("password hash is too weak: at least " + MIN_ITERATIONS
+                        + " iterations, 16 bytes of salt, a 32 byte hash");
+            }
+            return new Parsed(iterations, salt, hash);
+        } catch (IllegalArgumentException e) {
+            // NumberFormatException and a bad base64 are both IllegalArgumentException
+            throw new IllegalArgumentException("password hash is malformed or too weak (at least " + MIN_ITERATIONS
+                    + " iterations, 16 bytes of salt, a 32 byte hash)", e);
+        }
+    }
+
+    private static byte[] derive(char[] password, byte[] salt, int iterations, int bits) {
+        var spec = new PBEKeySpec(password, salt, iterations, bits);
+        try {
+            return SecretKeyFactory.getInstance("PBKDF2WithHmacSHA256").generateSecret(spec).getEncoded();
+        } catch (GeneralSecurityException e) {
+            throw new IllegalStateException("PBKDF2WithHmacSHA256 is part of every JDK", e);
+        } finally {
+            spec.clearPassword();
+        }
+    }
+}

backend/src/main/java/home/backend/adapters/auth/PasswordHashCli.java

@@ -0,0 +1,40 @@
+package home.backend.adapters.auth;
+
+import java.io.BufferedReader;
+import java.io.Console;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.io.PrintStream;
+import java.nio.charset.StandardCharsets;
+import java.util.Arrays;
+
+/** {@code hash-password}: prints the hash for USERS_FILE; on a terminal the password is asked twice, unechoed. */
+public final class PasswordHashCli {
+
+    private PasswordHashCli() {
+    }
+
+    /** @return the exit code */
+    public static int run(Console console, InputStream stdin, PrintStream out, PrintStream err) throws IOException {
+        char[] password;
+        if (console != null) {
+            password = console.readPassword("Password: ");
+            char[] again = console.readPassword("Again: ");
+            if (password == null || !Arrays.equals(password, again)) {
+                err.println("The passwords differ.");
+                return 1;
+            }
+        } else {
+            String line = new BufferedReader(new InputStreamReader(stdin, StandardCharsets.UTF_8)).readLine();
+            password = line == null ? null : line.toCharArray();
+        }
+        if (password == null || password.length == 0) {
+            err.println("No password given.");
+            return 1;
+        }
+        out.println(PasswordHash.create(password));
+        Arrays.fill(password, '\0');
+        return 0;
+    }
+}

backend/src/main/java/home/backend/adapters/auth/Session.java

@@ -0,0 +1,19 @@
+package home.backend.adapters.auth;
+
+import java.time.Instant;
+import java.util.regex.Pattern;
+
+/** Who is signed in and how. {@code method} is {@code local}, {@code oidc} or {@code none} (AUTH_DISABLED). */
+public record Session(String user, String method, Instant issuedAt) {
+
+    /** The name goes to the gateway's audit log as a header, so only plain characters are allowed. */
+    public static final String USER_PATTERN = "[\\w.@+-]{1,64}";
+    private static final Pattern USER = Pattern.compile(USER_PATTERN);
+
+    /** Every request is this one when authentication is switched off for development. */
+    static final Session OPEN = new Session("phone", "none", Instant.EPOCH);
+
+    public static boolean isValidUser(String name) {
+        return USER.matcher(name).matches();
+    }
+}

backend/src/main/java/home/backend/adapters/auth/Sessions.java

@@ -0,0 +1,40 @@
+package home.backend.adapters.auth;
+
+import java.time.Clock;
+import java.time.Duration;
+import java.time.Instant;
+import java.util.Map;
+import java.util.Optional;
+
+/** The session cookie: a signed token that holds the user, the method and when it was issued. */
+final class Sessions {
+
+    static final String COOKIE = "hp_session";
+    private static final String PURPOSE = "session";
+
+    private final SignedTokens tokens;
+    private final Clock clock;
+    private final Duration lifetime;
+
+    Sessions(SignedTokens tokens, Clock clock, Duration lifetime) {
+        this.tokens = tokens;
+        this.clock = clock;
+        this.lifetime = lifetime;
+    }
+
+    String setCookie(String user, String method) {
+        String token = tokens.issue(PURPOSE, lifetime, Map.of("user", user, "method", method,
+                "iat", String.valueOf(clock.instant().getEpochSecond())));
+        return Cookies.set(COOKIE, token, lifetime, "/");
+    }
+
+    String clearCookie() {
+        return Cookies.clear(COOKIE, "/");
+    }
+
+    Optional<Session> read(String cookieHeader) {
+        return Cookies.read(cookieHeader, COOKIE).flatMap(token -> tokens.read(PURPOSE, token)).map(claims ->
+                new Session(claims.get("user"), claims.get("method"),
+                        Instant.ofEpochSecond(Long.parseLong(claims.get("iat")))));
+    }
+}

backend/src/main/java/home/backend/adapters/auth/SignedTokens.java

@@ -0,0 +1,71 @@
+package home.backend.adapters.auth;
+
+import com.fasterxml.jackson.core.type.TypeReference;
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+import javax.crypto.Mac;
+import javax.crypto.spec.SecretKeySpec;
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.security.GeneralSecurityException;
+import java.security.MessageDigest;
+import java.time.Clock;
+import java.time.Duration;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Optional;
+
+/** Tamper-proof, expiring text for cookies: {@code base64url(json).base64url(HMAC-SHA256)}. */
+final class SignedTokens {
+
+    private static final ObjectMapper JSON = new ObjectMapper();
+    private static final TypeReference<Map<String, String>> CLAIMS = new TypeReference<>() {
+    };
+    private static final String HMAC = "HmacSHA256";
+
+    private final SecretKeySpec key;
+    private final Clock clock;
+
+    SignedTokens(byte[] secret, Clock clock) {
+        this.key = new SecretKeySpec(secret, HMAC);
+        this.clock = clock;
+    }
+
+    /** The purpose keeps a token made for one use (a session) from passing as another (a login in progress). */
+    String issue(String purpose, Duration lifetime, Map<String, String> claims) {
+        var all = new HashMap<>(claims);
+        all.put("purpose", purpose);
+        all.put("exp", String.valueOf(clock.instant().plus(lifetime).getEpochSecond()));
+        try {
+            String payload = Base64Url.encode(JSON.writeValueAsBytes(all));
+            return payload + "." + Base64Url.encode(sign(payload));
+        } catch (IOException e) {
+            throw new IllegalStateException(e);
+        }
+    }
+
+    Optional<Map<String, String>> read(String purpose, String token) {
+        try {
+            String[] parts = token.split("\\.", -1);
+            if (parts.length != 2 || !MessageDigest.isEqual(sign(parts[0]), Base64Url.decode(parts[1]))) {
+                return Optional.empty();
+            }
+            Map<String, String> claims = JSON.readValue(Base64Url.decode(parts[0]), CLAIMS);
+            boolean valid = purpose.equals(claims.get("purpose"))
+                    && Long.parseLong(claims.get("exp")) > clock.instant().getEpochSecond();
+            return valid ? Optional.of(claims) : Optional.empty();
+        } catch (IOException | IllegalArgumentException e) {
+            return Optional.empty();
+        }
+    }
+
+    private byte[] sign(String payload) {
+        try {
+            Mac mac = Mac.getInstance(HMAC);
+            mac.init(key);
+            return mac.doFinal(payload.getBytes(StandardCharsets.US_ASCII));
+        } catch (GeneralSecurityException e) {
+            throw new IllegalStateException(HMAC + " is part of every JDK", e);
+        }
+    }
+}

backend/src/main/java/home/backend/adapters/auth/UserStore.java

@@ -0,0 +1,151 @@
+package home.backend.adapters.auth;
+
+import com.fasterxml.jackson.core.type.TypeReference;
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+import java.io.IOException;
+import java.io.UncheckedIOException;
+import java.nio.channels.FileChannel;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.StandardCopyOption;
+import java.nio.file.StandardOpenOption;
+import java.nio.file.attribute.PosixFilePermissions;
+import java.security.SecureRandom;
+import java.util.Base64;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * The local accounts of USERS_FILE: {@code [{"username", "passwordHash"}]}. A missing file is an empty store
+ * (setup mode). Every change is written back atomically before it counts, under one lock.
+ */
+public final class UserStore {
+
+    public enum Removal { REMOVED, UNKNOWN, LAST }
+
+    private record Entry(String username, String passwordHash) {
+    }
+
+    private static final ObjectMapper JSON = new ObjectMapper();
+    /** What an unknown user is checked against, so that it costs as much as a wrong password. */
+    private static final String DECOY = PasswordHash.create(randomPassword());
+
+    private final Path file;
+    private Map<String, String> hashes;
+
+    UserStore(Path file, Map<String, String> hashes) {
+        this.file = file;
+        this.hashes = new LinkedHashMap<>(hashes);
+    }
+
+    /** @throws IllegalArgumentException when the file exists but is unreadable or holds a bad account */
+    public static UserStore load(Path file) {
+        Map<String, String> hashes = new LinkedHashMap<>();
+        if (Files.exists(file)) {
+            List<Entry> entries;
+            try {
+                entries = JSON.readValue(file.toFile(), new TypeReference<>() {
+                });
+            } catch (IOException e) {
+                throw new IllegalArgumentException("USERS_FILE " + file + " is not usable: " + e.getMessage(), e);
+            }
+            for (Entry entry : entries) {
+                if (entry.username() == null || !Session.isValidUser(entry.username())) {
+                    throw new IllegalArgumentException("USERS_FILE: a username must match " + Session.USER_PATTERN);
+                }
+                PasswordHash.requireValid(entry.passwordHash());
+                if (hashes.put(entry.username(), entry.passwordHash()) != null) {
+                    throw new IllegalArgumentException("USERS_FILE: duplicate username " + entry.username());
+                }
+            }
+        }
+        return new UserStore(file, hashes);
+    }
+
+    public synchronized boolean isEmpty() {
+        return hashes.isEmpty();
+    }
+
+    public synchronized boolean exists(String username) {
+        return hashes.containsKey(username);
+    }
+
+    public synchronized List<String> usernames() {
+        return List.copyOf(hashes.keySet());
+    }
+
+    public boolean authenticate(String username, char[] password) {
+        String stored;
+        synchronized (this) {
+            stored = hashes.get(username);
+        }
+        boolean matches = PasswordHash.matches(stored == null ? DECOY : stored, password);
+        return stored != null && matches;
+    }
+
+    /** The first account; false when there already is one, so only one setup can win. */
+    public synchronized boolean addFirst(String username, String hash) {
+        return hashes.isEmpty() && put(username, hash);
+    }
+
+    /** @return false when the name is taken */
+    public synchronized boolean add(String username, String hash) {
+        return !hashes.containsKey(username) && put(username, hash);
+    }
+
+    /** @return false when there is no such account */
+    public synchronized boolean changePassword(String username, String hash) {
+        return hashes.containsKey(username) && put(username, hash);
+    }
+
+    public synchronized Removal remove(String username) {
+        if (!hashes.containsKey(username)) {
+            return Removal.UNKNOWN;
+        }
+        if (hashes.size() == 1) {
+            return Removal.LAST;
+        }
+        var next = new LinkedHashMap<>(hashes);
+        next.remove(username);
+        write(next);
+        hashes = next;
+        return Removal.REMOVED;
+    }
+
+    private boolean put(String username, String hash) {
+        var next = new LinkedHashMap<>(hashes);
+        next.put(username, hash);
+        write(next);
+        hashes = next;
+        return true;
+    }
+
+    /** Temp file next to the target, synced, then renamed over it; the old file stays if anything fails. */
+    private void write(Map<String, String> accounts) {
+        Path directory = file.toAbsolutePath().getParent();
+        Path temp = null;
+        try {
+            temp = Files.createTempFile(directory, "users", ".tmp",
+                    PosixFilePermissions.asFileAttribute(PosixFilePermissions.fromString("rw-------")));
+            Files.write(temp, JSON.writerWithDefaultPrettyPrinter().writeValueAsBytes(accounts.entrySet().stream()
+                    .map(e -> new Entry(e.getKey(), e.getValue())).toList()));
+            try (FileChannel channel = FileChannel.open(temp, StandardOpenOption.WRITE)) {
+                channel.force(true);
+            }
+            Files.move(temp, file, StandardCopyOption.ATOMIC_MOVE);
+        } catch (IOException e) {
+            if (temp != null) {
+                temp.toFile().delete();
+            }
+            throw new UncheckedIOException("cannot write USERS_FILE " + file, e);
+        }
+    }
+
+    private static char[] randomPassword() {
+        byte[] bytes = new byte[24];
+        new SecureRandom().nextBytes(bytes);
+        return Base64.getEncoder().encodeToString(bytes).toCharArray();
+    }
+}

backend/src/main/java/home/backend/adapters/config/PresetFile.java

@@ -0,0 +1,41 @@
+package home.backend.adapters.config;
+
+import com.fasterxml.jackson.core.type.TypeReference;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import home.backend.domain.Preset;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.HashSet;
+import java.util.List;
+
+/** Reads the presets (F3) from the optional PRESETS_FILE, else the built-in list. */
+public final class PresetFile {
+
+    private static final ObjectMapper JSON = new ObjectMapper();
+    private static final TypeReference<List<Preset>> PRESETS = new TypeReference<>() {
+    };
+
+    private PresetFile() {
+    }
+
+    /** @param file null for the built-in defaults; IllegalArgumentException when it is unusable */
+    public static List<Preset> load(Path file) {
+        String source = file == null ? "built-in presets" : "PRESETS_FILE " + file;
+        try (InputStream in = file == null ? defaults() : Files.newInputStream(file)) {
+            List<Preset> presets = JSON.readValue(in, PRESETS);
+            if (new HashSet<>(presets.stream().map(Preset::id).toList()).size() != presets.size()) {
+                throw new IllegalArgumentException("preset ids must be unique");
+            }
+            return presets;
+        } catch (IOException | IllegalArgumentException e) {
+            throw new IllegalArgumentException(source + " is not usable: " + e.getMessage(), e);
+        }
+    }
+
+    private static InputStream defaults() {
+        return PresetFile.class.getResourceAsStream("/presets-default.json");
+    }
+}

backend/src/main/java/home/backend/adapters/gateway/GatewayHttpClient.java

@@ -0,0 +1,88 @@
+package home.backend.adapters.gateway;
+
+import com.fasterxml.jackson.databind.DeserializationFeature;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
+import home.backend.application.GatewayClient;
+import home.backend.domain.GatewaySnapshot;
+import home.backend.domain.GatewaySnapshot.DeviceSnapshot;
+import home.backend.domain.GatewaySnapshot.Measurement;
+
+import java.io.IOException;
+import java.net.URI;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
+import java.time.Duration;
+import java.time.Instant;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+/** Reads the gateway's {@code /health} and {@code /snapshot} over HTTP. */
+public class GatewayHttpClient implements GatewayClient {
+
+    private record Health(String version, List<DeviceHealth> devices) {
+    }
+
+    private record DeviceHealth(String name, String status, Instant lastSuccess, String lastError) {
+    }
+
+    private record DeviceReadings(String name, List<Reading> readings) {
+    }
+
+    private record Reading(String database, String measurement, Map<String, Double> fields, Instant time) {
+    }
+
+    // Unknown properties are ignored so the gateway can add fields without breaking us.
+    private static final ObjectMapper JSON = new ObjectMapper()
+            .registerModule(new JavaTimeModule())
+            .configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
+
+    private final URI baseUri;
+    private final Duration timeout;
+    private final HttpClient http;
+
+    public GatewayHttpClient(URI baseUri, Duration timeout) {
+        this.baseUri = baseUri;
+        this.timeout = timeout;
+        this.http = HttpClient.newBuilder().connectTimeout(timeout).build();
+    }
+
+    @Override
+    public GatewaySnapshot snapshot() throws IOException {
+        var health = JSON.readValue(get("/health", true), Health.class);
+        var readings = JSON.readValue(get("/snapshot", false), DeviceReadings[].class);
+        Map<String, List<Measurement>> measurements = Arrays.stream(readings)
+                .collect(Collectors.toMap(DeviceReadings::name, GatewayHttpClient::measurements));
+        var devices = health.devices().stream()
+                .map(device -> new DeviceSnapshot(device.name(), device.status().equals("UP"),
+                        device.lastSuccess(), device.lastError(),
+                        measurements.getOrDefault(device.name(), List.of())))
+                .toList();
+        return new GatewaySnapshot(health.version(), devices);
+    }
+
+    private static List<Measurement> measurements(DeviceReadings device) {
+        return device.readings().stream()
+                .map(r -> new Measurement(r.database(), r.measurement(), r.fields(), r.time()))
+                .toList();
+    }
+
+    /** A gateway with a device down answers /health with 503 and a valid body. */
+    private byte[] get(String path, boolean downIsValid) throws IOException {
+        var request = HttpRequest.newBuilder(baseUri.resolve(path)).timeout(timeout).GET().build();
+        try {
+            var response = http.send(request, HttpResponse.BodyHandlers.ofByteArray());
+            int status = response.statusCode();
+            if (status != 200 && !(downIsValid && status == 503)) {
+                throw new IOException("gateway " + path + " answered " + status);
+            }
+            return response.body();
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            throw new IOException("interrupted while calling gateway " + path, e);
+        }
+    }
+}

backend/src/main/java/home/backend/adapters/gateway/GatewayHttpCommands.java

@@ -0,0 +1,174 @@
+package home.backend.adapters.gateway;
+
+import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.databind.DeserializationFeature;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.SerializationFeature;
+import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
+import home.backend.application.GatewayBattery;
+import home.backend.application.GatewayCommands;
+import home.backend.application.GatewayRefresh;
+import home.backend.domain.BatteryChange;
+import home.backend.domain.BatteryResult;
+import home.backend.domain.BatteryView.Reserve;
+import home.backend.domain.Command;
+import home.backend.domain.CommandResult;
+import home.backend.domain.RefreshResult;
+import home.backend.domain.RestoreResult;
+import home.backend.domain.SetpointState;
+
+import java.io.IOException;
+import java.net.URI;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
+import java.time.Duration;
+import java.time.Instant;
+import java.util.List;
+import java.util.Set;
+
+/** Calls the gateway's {@code /commands}, {@code /battery} and {@code /refresh} with the shared token (S6). */
+public class GatewayHttpCommands implements GatewayCommands, GatewayBattery, GatewayRefresh {
+
+    /** The gateway answers a verdict with 200 (applied), 422 (rejected) or 502 (failed). */
+    private static final Set<Integer> VERDICTS = Set.of(200, 422, 502);
+
+    /** Restore now: 200 restored, 404 nothing pending, 409 changed meanwhile, 429 too soon, 502 failed. */
+    private static final Set<Integer> RESTORE_VERDICTS = Set.of(200, 404, 409, 429, 502);
+
+    /** Battery change: 200 applied, 422 rejected, 409 stale or changed meanwhile, 429 too soon, 502 failed. */
+    private static final Set<Integer> BATTERY_VERDICTS = Set.of(200, 422, 409, 429, 502);
+
+    @JsonInclude(JsonInclude.Include.NON_NULL)
+    private record ScheduleRequest(Boolean enabled, List<SlotRequest> slots) {
+    }
+
+    @JsonInclude(JsonInclude.Include.NON_NULL)
+    private record SlotRequest(int slot, Integer start, Integer soc, Boolean gridCharge) {
+    }
+
+    private record ReserveRequest(int pct) {
+    }
+
+    @JsonInclude(JsonInclude.Include.NON_NULL)
+    private record Request(String setpoint, int value, Long minutes, Instant until) {
+    }
+
+    private record RestoreRequest(String setpoint) {
+    }
+
+    private record Renewal(int renewed) {
+    }
+
+    private static final ObjectMapper JSON = new ObjectMapper()
+            .registerModule(new JavaTimeModule())
+            .disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS)
+            .configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
+
+    private final URI endpoint;
+    private final URI renewEndpoint;
+    private final URI restoreEndpoint;
+    private final URI refreshEndpoint;
+    private final URI reserveEndpoint;
+    private final URI scheduleEndpoint;
+    private final String token;
+    private final Duration timeout;
+    private final HttpClient http;
+
+    /** @param token null when not configured: every call then fails without touching the network */
+    public GatewayHttpCommands(URI baseUri, String token, Duration timeout) {
+        this.endpoint = baseUri.resolve("/commands");
+        this.renewEndpoint = baseUri.resolve("/commands/renew");
+        this.restoreEndpoint = baseUri.resolve("/commands/restore");
+        this.refreshEndpoint = baseUri.resolve("/refresh");
+        this.reserveEndpoint = baseUri.resolve("/battery/reserve");
+        this.scheduleEndpoint = baseUri.resolve("/battery/schedule");
+        this.token = token;
+        this.timeout = timeout;
+        this.http = HttpClient.newBuilder().connectTimeout(timeout).build();
+    }
+
+    @Override
+    public CommandResult apply(Command command) throws IOException {
+        Long minutes = command.duration() == null ? null : command.duration().toMinutes();
+        byte[] body = JSON.writeValueAsBytes(new Request(command.setpoint(), command.value(), minutes, command.heldUntil()));
+        HttpRequest.Builder request = request().header("Content-Type", "application/json")
+                .header("X-Requested-By", command.requestedBy())
+                .POST(HttpRequest.BodyPublishers.ofByteArray(body));
+        return JSON.readValue(send(request, VERDICTS), CommandResult.class);
+    }
+
+    @Override
+    public RestoreResult restore(String setpoint, String requestedBy) throws IOException {
+        byte[] body = JSON.writeValueAsBytes(new RestoreRequest(setpoint));
+        var request = request(restoreEndpoint).header("Content-Type", "application/json")
+                .header("X-Requested-By", requestedBy).POST(HttpRequest.BodyPublishers.ofByteArray(body));
+        return JSON.readValue(send(request, RESTORE_VERDICTS), RestoreResult.class);
+    }
+
+    @Override
+    public SetpointState setpoints() throws IOException {
+        return JSON.readValue(send(request().GET(), Set.of(200)), SetpointState.class);
+    }
+
+    @Override
+    public int renewLeases() throws IOException {
+        var request = request(renewEndpoint).POST(HttpRequest.BodyPublishers.noBody());
+        return JSON.readValue(send(request, Set.of(200)), Renewal.class).renewed();
+    }
+
+    @Override
+    public RefreshResult refresh() throws IOException {
+        var request = request(refreshEndpoint).POST(HttpRequest.BodyPublishers.noBody());
+        return JSON.readValue(send(request, Set.of(200)), RefreshResult.class);
+    }
+
+    @Override
+    public Reserve reserve() throws IOException {
+        return JSON.readValue(send(request(reserveEndpoint).GET(), Set.of(200)), Reserve.class);
+    }
+
+    @Override
+    public BatteryResult changeSchedule(BatteryChange change, String requestedBy) throws IOException {
+        var slots = change.slots().stream().map(slot -> new SlotRequest(slot.slot(),
+                slot.from() == null ? null : slot.from().getHour() * 100 + slot.from().getMinute(),
+                slot.socPct(), slot.gridCharge())).toList();
+        return battery(scheduleEndpoint, new ScheduleRequest(change.enabled(), slots), requestedBy);
+    }
+
+    @Override
+    public BatteryResult changeReserve(int pct, String requestedBy) throws IOException {
+        return battery(reserveEndpoint, new ReserveRequest(pct), requestedBy);
+    }
+
+    private BatteryResult battery(URI uri, Object body, String requestedBy) throws IOException {
+        var request = request(uri).header("Content-Type", "application/json").header("X-Requested-By", requestedBy)
+                .POST(HttpRequest.BodyPublishers.ofByteArray(JSON.writeValueAsBytes(body)));
+        return JSON.readValue(send(request, BATTERY_VERDICTS), BatteryResult.class);
+    }
+
+    private HttpRequest.Builder request() throws IOException {
+        return request(endpoint);
+    }
+
+    private HttpRequest.Builder request(URI uri) throws IOException {
+        if (token == null) {
+            throw new IOException("GATEWAY_TOKEN is not set, commands are disabled");
+        }
+        return HttpRequest.newBuilder(uri).timeout(timeout).header("Authorization", "Bearer " + token);
+    }
+
+    private byte[] send(HttpRequest.Builder request, Set<Integer> accepted) throws IOException {
+        try {
+            var built = request.build();
+            var response = http.send(built, HttpResponse.BodyHandlers.ofByteArray());
+            if (!accepted.contains(response.statusCode())) {
+                throw new IOException("gateway " + built.uri().getPath() + " answered " + response.statusCode());
+            }
+            return response.body();
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            throw new IOException("interrupted while calling the gateway", e);
+        }
+    }
+}

backend/src/main/java/home/backend/adapters/http/ApiServer.java

@@ -0,0 +1,487 @@
+package home.backend.adapters.http;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.DeserializationFeature;
+import com.fasterxml.jackson.databind.MapperFeature;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.SerializationFeature;
+import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
+import com.sun.net.httpserver.HttpExchange;
+import com.sun.net.httpserver.HttpHandler;
+import com.sun.net.httpserver.HttpServer;
+import home.backend.adapters.auth.Authentication;
+import home.backend.application.AuditService;
+import home.backend.application.BatteryService;
+import home.backend.application.EnergyDetailsService;
+import home.backend.application.EnergyService;
+import home.backend.application.GatewayRefresh;
+import home.backend.application.HealthService;
+import home.backend.application.HeatPumpService;
+import home.backend.application.HistoryService;
+import home.backend.application.ProgramService;
+import home.backend.application.StatsService;
+import home.backend.application.PiSensorService;
+import home.backend.application.SetpointService;
+import home.backend.application.WeatherService;
+import home.backend.domain.BatteryChange;
+import home.backend.domain.BatteryResult;
+import home.backend.domain.CommandResult.Status;
+import home.backend.domain.PresetResult;
+import home.backend.domain.RestoreResult;
+
+import java.io.IOException;
+import java.time.OffsetDateTime;
+import java.time.format.DateTimeParseException;
+import java.net.InetSocketAddress;
+import java.net.URLDecoder;
+import java.nio.charset.StandardCharsets;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.regex.Pattern;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+
+/** The phone-facing JSON API under {@code /api/} and the static web UI. */
+public class ApiServer {
+
+    private static final ObjectMapper JSON = new ObjectMapper()
+            .registerModule(new JavaTimeModule())
+            .disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS)
+            // 45.5 or "45" must not silently become 45 in a request that writes to a heat pump.
+            .disable(DeserializationFeature.ACCEPT_FLOAT_AS_INT)
+            .disable(MapperFeature.ALLOW_COERCION_OF_SCALARS);
+
+    private record ReserveRequest(Integer pct) {
+    }
+
+    private record SetpointRequest(String setpoint, Integer value, Double hours) {
+    }
+
+    /**
+     * {@code hours}: how long a timed preset lasts; {@code values}: the user's own value per setpoint of the
+     * preset, by setpoint name.
+     */
+    private record PresetRequest(String until, Integer hours, Map<String, Integer> values) {
+
+        PresetRequest {
+            if (values == null) {
+                values = Map.of();
+            } else if (values.containsValue(null)) {
+                throw new IllegalArgumentException("a value must be a number");
+            }
+        }
+    }
+
+    private static final String UNREACHABLE = "gateway unreachable";
+    private static final String UNAVAILABLE = "battery changes are not available: gateway unreachable or not enabled";
+    private static final String WRITE_MARKER = "home-pump";
+    private static final String PRESETS_PATH = "/api/presets/";
+    private static final String SETPOINTS_PATH = "/api/setpoints/";
+    private static final Pattern RESTORE_PATH = Pattern.compile("/api/setpoints/([a-z_]{1,32})/restore");
+    private static final SecurityHeaders SECURITY_HEADERS = new SecurityHeaders();
+
+    /** A setpoint request is a few dozen bytes; anything near this is not from our UI. */
+    private static final int MAX_BODY_BYTES = 4096;
+    private static final int STOP_GRACE_SECONDS = 5;
+
+    private final HttpServer server;
+    private final SessionFilter sessionFilter;
+    private final ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor();
+
+    /** Binds the port now; 0 picks a free one. */
+    public ApiServer(int port, HeatPumpService heatPump, EnergyService energy,
+            EnergyDetailsService energyDetails, HealthService health,
+            HistoryService history, SetpointService setpoints, PiSensorService piSensor,
+            BatteryService battery, AuditService audit, StatsService stats, ProgramService program, WeatherService weather,
+            GatewayRefresh refresh, Authentication auth) throws IOException {
+        server = HttpServer.create(new InetSocketAddress(port), 0);
+        server.setExecutor(executor);
+        sessionFilter = new SessionFilter(auth);
+        // Everything outside the API, with the security headers too: the web UI is the frontend's (ADR-010).
+        open("/", exchange -> {
+            try (exchange) {
+                exchange.sendResponseHeaders(404, -1);
+            }
+        });
+        var signIn = new AuthEndpoints(auth);
+        openRoute("/api/auth/config", signIn::config);
+        openRoute("/api/auth/login", signIn::login);
+        openRoute("/api/auth/logout", signIn::logout);
+        openRoute("/api/auth/me", signIn::me);
+        openRoute("/api/auth/setup", signIn::setup);
+        openRoute("/api/auth/users", signIn::users);
+        openRoute("/api/auth/password", signIn::password);
+        open("/api/auth/users/", signIn::deleteUser);
+        openRoute("/api/auth/oidc/start", signIn::oidcStart);
+        openRoute("/api/auth/oidc/callback", signIn::oidcCallback);
+        // The container healthcheck: no session, nothing in the answer.
+        openRoute("/api/live", exchange -> handle(exchange, Map.of("GET", () -> {
+            exchange.sendResponseHeaders(200, 2);
+            exchange.getResponseBody().write("ok".getBytes(StandardCharsets.US_ASCII));
+        })));
+        api("/api/heat-pump", query -> heatPump.current());
+        api("/api/energy", query -> energy.current());
+        api("/api/energy/details", query -> energyDetails.current());
+        api("/api/battery", query -> battery.current());
+        route("/api/battery/schedule", exchange -> handle(exchange, Map.of(
+                "POST", () -> guarded(exchange, body -> postSchedule(exchange, body, battery)))));
+        route("/api/battery/reserve", exchange -> handle(exchange, Map.of(
+                "POST", () -> guarded(exchange, body -> postReserve(exchange, body, battery)))));
+        route("/api/refresh", exchange -> handle(exchange, Map.of(
+                "POST", () -> guarded(exchange, body -> postRefresh(exchange, refresh)))));
+        api("/api/pi-sensor", query -> piSensor.current());
+        api("/api/weather", query -> weather.current());
+        api("/api/health", query -> health.current());
+        route("/api/history", exchange -> handleHistory(exchange, history));
+        route("/api/audit", exchange -> handleAudit(exchange, audit));
+        route("/api/stats", exchange -> handleStats(exchange, stats));
+        route("/api/program", exchange -> handleProgram(exchange, program));
+        route("/api/setpoints", exchange -> handle(exchange, Map.of(
+                "GET", () -> getSetpoints(exchange, setpoints),
+                "POST", () -> guarded(exchange, body -> postSetpoint(exchange, body, setpoints)))));
+        context(SETPOINTS_PATH, exchange -> {
+            var restore = RESTORE_PATH.matcher(exchange.getRequestURI().getPath());
+            if (restore.matches()) {
+                handle(exchange, Map.of("POST", () -> guarded(exchange,
+                        body -> postRestore(exchange, restore.group(1), setpoints))));
+            } else {
+                try (exchange) {
+                    exchange.sendResponseHeaders(404, -1);
+                }
+            }
+        });
+        context(PRESETS_PATH, exchange -> handle(exchange, Map.of(
+                "POST", () -> guarded(exchange, body -> postPreset(exchange, body, setpoints)))));
+    }
+
+    private void route(String path, HttpHandler handler) {
+        context(path, exactly(path, handler));
+    }
+
+    private void openRoute(String path, HttpHandler handler) {
+        open(path, exactly(path, handler));
+    }
+
+    /** The JDK matches a context by prefix, so /api/heat-pumpX would reach /api/heat-pump. */
+    private static HttpHandler exactly(String path, HttpHandler handler) {
+        return exchange -> {
+            if (path.equals(exchange.getRequestURI().getPath())) {
+                handler.handle(exchange);
+            } else {
+                try (exchange) {
+                    exchange.sendResponseHeaders(404, -1);
+                }
+            }
+        };
+    }
+
+    /** Needs a session. */
+    private void context(String path, HttpHandler handler) {
+        var context = server.createContext(path, handler);
+        context.getFilters().add(SECURITY_HEADERS);
+        context.getFilters().add(sessionFilter);
+    }
+
+    /** Answers without a session. */
+    private void open(String path, HttpHandler handler) {
+        server.createContext(path, handler).getFilters().add(SECURITY_HEADERS);
+    }
+
+    public void start() {
+        server.start();
+    }
+
+    public void stop() {
+        server.stop(STOP_GRACE_SECONDS);
+        executor.shutdown();
+    }
+
+    public int port() {
+        return server.getAddress().getPort();
+    }
+
+    private interface Gateway {
+        Object get(Map<String, String> query) throws IOException;
+    }
+
+    /** Gateway trouble on a live-state endpoint is the gateway being unreachable: 503. */
+    private void api(String path, Gateway gateway) {
+        route(path, exchange -> handle(exchange, Map.of("GET", () -> {
+            try {
+                send(exchange, 200, gateway.get(Map.of()));
+            } catch (IOException e) {
+                send(exchange, 503, error(UNREACHABLE));
+            }
+        })));
+    }
+
+    /**
+     * A page on another site can make the browser send a simple POST with the user's cookies. It cannot
+     * add a custom header, set a JSON content type or fake the Origin, so a write needs all three.
+     */
+    static void guarded(HttpExchange exchange, Write write) throws IOException {
+        var headers = exchange.getRequestHeaders();
+        String origin = headers.getFirst("Origin");
+        if (origin != null && !origin.endsWith("//" + headers.getFirst("Host"))) {
+            send(exchange, 403, error("cross-site request"));
+        } else if (!WRITE_MARKER.equals(headers.getFirst("X-Requested-With"))) {
+            send(exchange, 403, error("missing X-Requested-With: " + WRITE_MARKER));
+        } else if (!isJson(headers.getFirst("Content-Type"))) {
+            send(exchange, 415, error("expected Content-Type: application/json"));
+        } else {
+            byte[] body = exchange.getRequestBody().readNBytes(MAX_BODY_BYTES + 1);
+            if (body.length > MAX_BODY_BYTES) {
+                send(exchange, 413, error("request body over " + MAX_BODY_BYTES + " bytes"));
+            } else {
+                write.run(body);
+            }
+        }
+    }
+
+    private static boolean isJson(String contentType) {
+        return contentType != null && contentType.split(";")[0].trim().equalsIgnoreCase("application/json");
+    }
+
+    private static void getSetpoints(HttpExchange exchange, SetpointService setpoints) throws IOException {
+        try {
+            send(exchange, 200, setpoints.current());
+        } catch (IOException e) {
+            send(exchange, 503, error(UNREACHABLE));
+        }
+    }
+
+    private static void postSetpoint(HttpExchange exchange, byte[] body, SetpointService setpoints)
+            throws IOException {
+        try {
+            var request = JSON.readValue(body, SetpointRequest.class);
+            if (request == null || request.setpoint() == null || request.value() == null) {
+                throw new IllegalArgumentException("setpoint and value are required");
+            }
+            var result = setpoints.apply(request.setpoint(), request.value(), request.hours(), user(exchange));
+            send(exchange, httpStatus(result.status()), result);
+        } catch (JsonProcessingException | IllegalArgumentException e) {
+            send(exchange, 400, error("expected {\"setpoint\", \"value\", \"hours\"?}"));
+        } catch (IOException e) {
+            send(exchange, 503, error(UNREACHABLE));
+        }
+    }
+
+    private static void postSchedule(HttpExchange exchange, byte[] body, BatteryService battery) throws IOException {
+        try {
+            var change = JSON.readValue(body, BatteryChange.class);
+            if (change == null) {
+                throw new IllegalArgumentException("a change is required");
+            }
+            var result = battery.changeSchedule(change, user(exchange));
+            send(exchange, batteryHttpStatus(result.status()), result);
+        } catch (JsonProcessingException | IllegalArgumentException e) {
+            send(exchange, 400, error("expected {\"enabled\"?, \"slots\": [{\"slot\", \"from\"?: \"HH:MM\", "
+                    + "\"socPct\"?, \"gridCharge\"?}]}"));
+        } catch (IOException e) {
+            send(exchange, 503, error(UNAVAILABLE));
+        }
+    }
+
+    private static void postReserve(HttpExchange exchange, byte[] body, BatteryService battery) throws IOException {
+        try {
+            var request = JSON.readValue(body, ReserveRequest.class);
+            if (request == null || request.pct() == null) {
+                throw new IllegalArgumentException("pct is required");
+            }
+            var result = battery.changeReserve(request.pct(), user(exchange));
+            send(exchange, batteryHttpStatus(result.status()), result);
+        } catch (JsonProcessingException | IllegalArgumentException e) {
+            send(exchange, 400, error("expected {\"pct\"}"));
+        } catch (IOException e) {
+            send(exchange, 503, error(UNAVAILABLE));
+        }
+    }
+
+    private static void postRefresh(HttpExchange exchange, GatewayRefresh refresh) throws IOException {
+        try {
+            send(exchange, 200, refresh.refresh());
+        } catch (IOException e) {
+            send(exchange, 503, error(UNREACHABLE));
+        }
+    }
+
+    private static void postRestore(HttpExchange exchange, String setpoint, SetpointService setpoints)
+            throws IOException {
+        try {
+            var result = setpoints.restore(setpoint, user(exchange));
+            send(exchange, restoreHttpStatus(result.outcome()), result);
+        } catch (IOException e) {
+            send(exchange, 503, error(UNREACHABLE));
+        }
+    }
+
+    private static void postPreset(HttpExchange exchange, byte[] body, SetpointService setpoints)
+            throws IOException {
+        String id = exchange.getRequestURI().getPath().substring(PRESETS_PATH.length());
+        try {
+            var request = body.length == 0 ? new PresetRequest(null, null, null) : JSON.readValue(body, PresetRequest.class);
+            var until = request.until() == null ? null : OffsetDateTime.parse(request.until()).toInstant();
+            var result = setpoints.applyPreset(id, until, request.hours(), request.values(),
+                    user(exchange));
+            if (result.isPresent()) {
+                send(exchange, presetHttpStatus(result.get().status()), result.get());
+            } else {
+                send(exchange, 404, error("no such preset"));
+            }
+        } catch (SetpointService.InvalidHoursException e) {
+            send(exchange, 400, error("invalid_hours"));
+        } catch (JsonProcessingException | DateTimeParseException | IllegalArgumentException e) {
+            send(exchange, 400, error("expected {\"until\": \"2026-11-02T18:00:00+01:00\"} for a preset that needs "
+                    + "an end time, else no body; optional \"values\": {\"cwu_comfort\": 12} within the limits "
+                    + "for setpoints of the preset"));
+        } catch (IOException e) {
+            send(exchange, 503, error(UNREACHABLE));
+        }
+    }
+
+    private static int httpStatus(Status status) {
+        return switch (status) {
+            case APPLIED -> 200;
+            case REJECTED -> 422;
+            case FAILED -> 502;
+        };
+    }
+
+    private static int batteryHttpStatus(BatteryResult.Status status) {
+        return switch (status) {
+            case APPLIED -> 200;
+            case REJECTED -> 422;
+            case STALE -> 409;
+            case TOO_SOON -> 429;
+            case FAILED -> 502;
+        };
+    }
+
+    private static int restoreHttpStatus(RestoreResult.Outcome outcome) {
+        return switch (outcome) {
+            case RESTORED -> 200;
+            case NOT_PENDING -> 404;
+            case CONFLICT -> 409;
+            case TOO_SOON -> 429;
+            case FAILED -> 502;
+        };
+    }
+
+    private static int presetHttpStatus(PresetResult.Status status) {
+        return switch (status) {
+            case APPLIED -> 200;
+            case REJECTED -> 422;
+            case FAILED, PARTIAL -> 502;
+        };
+    }
+
+    /** The signed-in user, set by the session filter. */
+    private static String user(HttpExchange exchange) {
+        return (String) exchange.getAttribute(SessionFilter.USER_ATTRIBUTE);
+    }
+
+    private void handleHistory(HttpExchange exchange, HistoryService history) throws IOException {
+        handle(exchange, Map.of("GET", () -> {
+            Map<String, String> query = parseQuery(exchange.getRequestURI().getRawQuery());
+            try {
+                send(exchange, 200, history.history(query.get("series"), query.get("range")));
+            } catch (IllegalArgumentException e) {
+                send(exchange, 400, error(e.getMessage()));
+            } catch (IOException e) {
+                send(exchange, 502, error("history unavailable"));
+            }
+        }));
+    }
+
+    private void handleAudit(HttpExchange exchange, AuditService audit) throws IOException {
+        handle(exchange, Map.of("GET", () -> {
+            Map<String, String> query = parseQuery(exchange.getRequestURI().getRawQuery());
+            try {
+                send(exchange, 200, audit.audit(query.get("range")));
+            } catch (IllegalArgumentException e) {
+                send(exchange, 400, error(e.getMessage()));
+            } catch (IOException e) {
+                send(exchange, 502, error("audit unavailable"));
+            }
+        }));
+    }
+
+    private void handleStats(HttpExchange exchange, StatsService stats) throws IOException {
+        handle(exchange, Map.of("GET", () -> {
+            try {
+                send(exchange, 200, stats.stats(parseQuery(exchange.getRequestURI().getRawQuery()).get("range")));
+            } catch (IllegalArgumentException e) {
+                send(exchange, 400, error(e.getMessage()));
+            } catch (IOException e) {
+                send(exchange, 502, error("stats unavailable"));
+            }
+        }));
+    }
+
+    private void handleProgram(HttpExchange exchange, ProgramService program) throws IOException {
+        handle(exchange, Map.of("GET", () -> {
+            try {
+                send(exchange, 200, program.program(parseQuery(exchange.getRequestURI().getRawQuery()).get("days")));
+            } catch (IllegalArgumentException e) {
+                send(exchange, 400, error(e.getMessage()));
+            } catch (IOException e) {
+                send(exchange, 502, error("program unavailable"));
+            }
+        }));
+    }
+
+    interface Action {
+        void run() throws IOException;
+    }
+
+    interface Write {
+        void run(byte[] body) throws IOException;
+    }
+
+    static void handle(HttpExchange exchange, Map<String, Action> byMethod) throws IOException {
+        try (exchange) {
+            Action action = byMethod.get(exchange.getRequestMethod());
+            if (action == null) {
+                exchange.sendResponseHeaders(405, -1);
+                return;
+            }
+            try {
+                action.run();
+            } catch (RuntimeException e) {
+                // A gateway payload the client could not map (duplicate device, missing status): answer, do not drop.
+                System.err.println("home-pump-backend: " + exchange.getRequestURI().getPath() + ": " + e);
+                if (exchange.getResponseCode() == -1) {
+                    send(exchange, 502, error("bad gateway response"));
+                }
+            }
+        }
+    }
+
+    static void send(HttpExchange exchange, int status, Object body) throws IOException {
+        byte[] bytes = JSON.writeValueAsBytes(body);
+        exchange.getResponseHeaders().set("Content-Type", "application/json");
+        exchange.getResponseHeaders().set("Cache-Control", "no-store");
+        exchange.sendResponseHeaders(status, bytes.length);
+        exchange.getResponseBody().write(bytes);
+    }
+
+    private static Map<String, String> error(String message) {
+        return Map.of("error", message);
+    }
+
+    static Map<String, String> parseQuery(String raw) {
+        Map<String, String> query = new HashMap<>();
+        if (raw == null) {
+            return query;
+        }
+        for (String pair : raw.split("&")) {
+            String[] kv = pair.split("=", 2);
+            query.put(decode(kv[0]), kv.length == 2 ? decode(kv[1]) : "");
+        }
+        return query;
+    }
+
+    private static String decode(String s) {
+        return URLDecoder.decode(s, StandardCharsets.UTF_8);
+    }
+}

backend/src/main/java/home/backend/adapters/http/AuthEndpoints.java

@@ -0,0 +1,284 @@
+package home.backend.adapters.http;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.sun.net.httpserver.HttpExchange;
+import home.backend.adapters.auth.Authentication;
+import home.backend.adapters.auth.OidcException;
+import home.backend.adapters.auth.Session;
+
+import java.io.IOException;
+import java.util.Map;
+import java.util.regex.Pattern;
+
+/** The endpoints under {@code /api/auth/}: sign-in needs no session, managing accounts does. */
+final class AuthEndpoints {
+
+    private record LoginRequest(String username, String password) {
+    }
+
+    private record PasswordRequest(String current, @JsonProperty("new") String next) {
+    }
+
+    private static final Pattern DELETE_PATH = Pattern.compile("/api/auth/users/([^/]{1,64})/delete");
+    private static final ObjectMapper JSON = new ObjectMapper();
+    private static final int MAX_CREDENTIAL_LENGTH = 256;
+
+    private final Authentication auth;
+
+    AuthEndpoints(Authentication auth) {
+        this.auth = auth;
+    }
+
+    void config(HttpExchange exchange) throws IOException {
+        ApiServer.handle(exchange, Map.of("GET", () -> ApiServer.send(exchange, 200,
+                Map.of("local", auth.localEnabled(), "oidc", auth.oidcEnabled(),
+                        "setup", auth.setupNeeded()))));
+    }
+
+    void login(HttpExchange exchange) throws IOException {
+        ApiServer.handle(exchange, Map.of("POST", () -> ApiServer.guarded(exchange, body -> postLogin(exchange, body))));
+    }
+
+    void logout(HttpExchange exchange) throws IOException {
+        ApiServer.handle(exchange, Map.of("POST", () -> ApiServer.guarded(exchange, body -> {
+            String cookie = auth.clearedSessionCookie();
+            if (!cookie.isEmpty()) {
+                exchange.getResponseHeaders().add("Set-Cookie", cookie);
+            }
+            exchange.sendResponseHeaders(204, -1);
+        })));
+    }
+
+    void me(HttpExchange exchange) throws IOException {
+        ApiServer.handle(exchange, Map.of("GET", () -> {
+            var session = auth.session(SessionFilter.cookies(exchange));
+            if (session.isPresent()) {
+                ApiServer.send(exchange, 200, user(session.get()));
+            } else {
+                ApiServer.send(exchange, 401, Map.of("error", "unauthenticated"));
+            }
+        }));
+    }
+
+    void oidcStart(HttpExchange exchange) throws IOException {
+        ApiServer.handle(exchange, Map.of("GET", () -> {
+            if (!auth.oidcEnabled()) {
+                exchange.sendResponseHeaders(404, -1);
+                return;
+            }
+            try {
+                var start = auth.oidc().start();
+                exchange.getResponseHeaders().add("Set-Cookie", start.setCookie());
+                redirect(exchange, start.location().toString());
+            } catch (OidcException e) {
+                redirectWithError(exchange, e);
+            }
+        }));
+    }
+
+    void oidcCallback(HttpExchange exchange) throws IOException {
+        ApiServer.handle(exchange, Map.of("GET", () -> {
+            if (!auth.oidcEnabled()) {
+                exchange.sendResponseHeaders(404, -1);
+                return;
+            }
+            exchange.getResponseHeaders().add("Set-Cookie", auth.oidc().clearCookie());
+            try {
+                String name = auth.oidc().callback(ApiServer.parseQuery(exchange.getRequestURI().getRawQuery()),
+                        SessionFilter.cookies(exchange));
+                exchange.getResponseHeaders().add("Set-Cookie", auth.sessionCookie(name, "oidc"));
+                redirect(exchange, "/");
+            } catch (OidcException e) {
+                redirectWithError(exchange, e);
+            }
+        }));
+    }
+
+    private void postLogin(HttpExchange exchange, byte[] body) throws IOException {
+        if (!auth.localEnabled()) {
+            ApiServer.send(exchange, 404, Map.of("error", "local login is not enabled"));
+            return;
+        }
+        LoginRequest request = credentials(exchange, body);
+        if (request == null) {
+            return;
+        }
+        String ip = ClientIp.of(exchange, auth.proxyHops());
+        var login = auth.login(request.username(), request.password().toCharArray(), ip);
+        switch (login.status()) {
+            case OK -> {
+                exchange.getResponseHeaders().add("Set-Cookie", auth.sessionCookie(request.username(), "local"));
+                ApiServer.send(exchange, 200, Map.of("user", request.username(), "method", "local"));
+            }
+            case INVALID -> {
+                System.err.println("home-pump-backend: failed login from " + ip);
+                ApiServer.send(exchange, 401, Map.of("error", "invalid"));
+            }
+            case THROTTLED -> throttled(exchange, login);
+        }
+    }
+
+    /** The username and password of the body, or null after answering 400. */
+    private static LoginRequest credentials(HttpExchange exchange, byte[] body) throws IOException {
+        LoginRequest request;
+        try {
+            request = JSON.readValue(body, LoginRequest.class);
+        } catch (JsonProcessingException e) {
+            request = null;
+        }
+        if (request == null || request.username() == null || request.password() == null
+                || request.username().length() > MAX_CREDENTIAL_LENGTH
+                || request.password().length() > MAX_CREDENTIAL_LENGTH) {
+            ApiServer.send(exchange, 400, Map.of("error", "expected {\"username\", \"password\"}"));
+            return null;
+        }
+        return request;
+    }
+
+    private static void throttled(HttpExchange exchange, Authentication.Login login) throws IOException {
+        exchange.getResponseHeaders().set("Retry-After", String.valueOf(login.retryAfterSeconds()));
+        ApiServer.send(exchange, 429, Map.of("error", "throttled", "retryAfterSeconds", login.retryAfterSeconds()));
+    }
+
+    /** True when the name and password may become an account; else answers 400. */
+    private static boolean acceptable(HttpExchange exchange, String username, String password) throws IOException {
+        if (!Session.isValidUser(username)) {
+            ApiServer.send(exchange, 400, Map.of("error", "invalid_username"));
+            return false;
+        }
+        if (!Authentication.strongEnough(password)) {
+            ApiServer.send(exchange, 400, Map.of("error", "weak_password"));
+            return false;
+        }
+        return true;
+    }
+
+    void setup(HttpExchange exchange) throws IOException {
+        ApiServer.handle(exchange, Map.of("POST", () -> ApiServer.guarded(exchange, body -> {
+            if (!auth.localEnabled()) {
+                ApiServer.send(exchange, 404, Map.of("error", "local login is not enabled"));
+                return;
+            }
+            LoginRequest request = credentials(exchange, body);
+            if (request == null) {
+                return;
+            }
+            if (!auth.setupNeeded()) {
+                ApiServer.send(exchange, 409, Map.of("error", "setup_done"));
+                return;
+            }
+            if (!acceptable(exchange, request.username(), request.password())) {
+                return;
+            }
+            var result = auth.setup(request.username(), request.password().toCharArray(),
+                    ClientIp.of(exchange, auth.proxyHops()));
+            switch (result.status()) {
+                case OK -> {
+                    exchange.getResponseHeaders().add("Set-Cookie", auth.sessionCookie(request.username(), "local"));
+                    ApiServer.send(exchange, 200, Map.of("user", request.username(), "method", "local"));
+                }
+                case INVALID -> ApiServer.send(exchange, 409, Map.of("error", "setup_done"));
+                case THROTTLED -> throttled(exchange, result);
+            }
+        })));
+    }
+
+    /** Runs the action for a signed-in user of a configured local store; else answers 401 or 404. */
+    private void asUser(HttpExchange exchange, SignedIn action) throws IOException {
+        var session = auth.session(SessionFilter.cookies(exchange));
+        if (session.isEmpty()) {
+            ApiServer.send(exchange, 401, Map.of("error", "unauthenticated"));
+        } else if (!auth.localEnabled()) {
+            ApiServer.send(exchange, 404, Map.of("error", "local login is not enabled"));
+        } else {
+            action.run(session.get());
+        }
+    }
+
+    private interface SignedIn {
+        void run(Session session) throws IOException;
+    }
+
+    void users(HttpExchange exchange) throws IOException {
+        ApiServer.handle(exchange, Map.of(
+                "GET", () -> asUser(exchange, session -> ApiServer.send(exchange, 200,
+                        auth.usernames().stream().map(name -> Map.of("username", name)).toList())),
+                "POST", () -> ApiServer.guarded(exchange, body -> asUser(exchange, session -> {
+                    LoginRequest request = credentials(exchange, body);
+                    if (request == null || !acceptable(exchange, request.username(), request.password())) {
+                        return;
+                    }
+                    if (auth.addUser(session.user(), request.username(), request.password().toCharArray())) {
+                        ApiServer.send(exchange, 200, Map.of("username", request.username()));
+                    } else {
+                        ApiServer.send(exchange, 409, Map.of("error", "exists"));
+                    }
+                }))));
+    }
+
+    void password(HttpExchange exchange) throws IOException {
+        ApiServer.handle(exchange, Map.of("POST", () -> ApiServer.guarded(exchange, body -> asUser(exchange, session -> {
+            PasswordRequest request;
+            try {
+                request = JSON.readValue(body, PasswordRequest.class);
+            } catch (JsonProcessingException e) {
+                request = null;
+            }
+            if (request == null || request.current() == null || request.next() == null
+                    || request.current().length() > MAX_CREDENTIAL_LENGTH
+                    || request.next().length() > MAX_CREDENTIAL_LENGTH) {
+                ApiServer.send(exchange, 400, Map.of("error", "expected {\"current\", \"new\"}"));
+            } else if (!Authentication.LOCAL.equals(session.method())) {
+                ApiServer.send(exchange, 403, Map.of("error", "local_only"));
+            } else if (!Authentication.strongEnough(request.next())) {
+                ApiServer.send(exchange, 400, Map.of("error", "weak_password"));
+            } else {
+                var result = auth.changePassword(session.user(), request.current().toCharArray(),
+                        request.next().toCharArray(), ClientIp.of(exchange, auth.proxyHops()));
+                switch (result.status()) {
+                    case OK -> exchange.sendResponseHeaders(204, -1);
+                    case INVALID -> ApiServer.send(exchange, 401, Map.of("error", "invalid"));
+                    case THROTTLED -> throttled(exchange, result);
+                }
+            }
+        }))));
+    }
+
+    void deleteUser(HttpExchange exchange) throws IOException {
+        ApiServer.handle(exchange, Map.of("POST", () -> ApiServer.guarded(exchange, body -> asUser(exchange, session -> {
+            var path = DELETE_PATH.matcher(exchange.getRequestURI().getRawPath());
+            if (!path.matches()) {
+                exchange.sendResponseHeaders(404, -1);
+                return;
+            }
+            String name = path.group(1);
+            switch (auth.removeUser(session.user(), name)) {
+                case UNKNOWN -> ApiServer.send(exchange, 404, Map.of("error", "unknown_user"));
+                case LAST -> ApiServer.send(exchange, 409, Map.of("error", "last_user"));
+                case REMOVED -> {
+                    if (name.equals(session.user())) {
+                        exchange.getResponseHeaders().add("Set-Cookie", auth.clearedSessionCookie());
+                    }
+                    exchange.sendResponseHeaders(204, -1);
+                }
+            }
+        }))));
+    }
+
+    private static Map<String, String> user(Session session) {
+        return Map.of("user", session.user(), "method", session.method());
+    }
+
+    private static void redirectWithError(HttpExchange exchange, OidcException e) throws IOException {
+        System.err.println("home-pump-backend: OIDC sign-in failed: " + e.getMessage());
+        redirect(exchange, "/#login?error=" + e.reason().code());
+    }
+
+    private static void redirect(HttpExchange exchange, String location) throws IOException {
+        exchange.getResponseHeaders().set("Location", location);
+        exchange.getResponseHeaders().set("Cache-Control", "no-store");
+        exchange.sendResponseHeaders(302, -1);
+    }
+}

backend/src/main/java/home/backend/adapters/http/ClientIp.java

@@ -0,0 +1,29 @@
+package home.backend.adapters.http;
+
+import com.sun.net.httpserver.HttpExchange;
+
+import java.util.Arrays;
+import java.util.List;
+
+/**
+ * The client's address for the login throttle. Each trusted proxy appends the address it saw to
+ * X-Forwarded-For, so the entry {@code hops} from the right is the first one no trusted proxy vouches for
+ * beyond that; anything the client put in front of it is ignored. Without enough entries the request did not
+ * come through the proxies, and the socket's address is used.
+ */
+final class ClientIp {
+
+    private ClientIp() {
+    }
+
+    static String of(HttpExchange exchange, int hops) {
+        List<String> values = exchange.getRequestHeaders().get("X-Forwarded-For");
+        if (values != null) {
+            List<String> chain = Arrays.stream(String.join(",", values).split(",")).map(String::trim).toList();
+            if (chain.size() >= hops && !chain.get(chain.size() - hops).isEmpty()) {
+                return chain.get(chain.size() - hops);
+            }
+        }
+        return exchange.getRemoteAddress().getAddress().getHostAddress();
+    }
+}

backend/src/main/java/home/backend/adapters/http/SecurityHeaders.java

@@ -0,0 +1,28 @@
+package home.backend.adapters.http;
+
+import com.sun.net.httpserver.Filter;
+import com.sun.net.httpserver.HttpExchange;
+
+import java.io.IOException;
+
+/** Sets the browser hardening headers on every response, whatever handler answers. */
+final class SecurityHeaders extends Filter {
+
+    private static final String POLICY = "default-src 'none'; script-src 'self'; style-src 'self'; "
+            + "img-src 'self' data:; font-src 'self'; connect-src 'self'; base-uri 'none'; "
+            + "form-action 'self'; frame-ancestors 'none'";
+
+    @Override
+    public void doFilter(HttpExchange exchange, Chain chain) throws IOException {
+        var headers = exchange.getResponseHeaders();
+        headers.set("Content-Security-Policy", POLICY);
+        headers.set("X-Content-Type-Options", "nosniff");
+        headers.set("Referrer-Policy", "no-referrer");
+        chain.doFilter(exchange);
+    }
+
+    @Override
+    public String description() {
+        return "security headers";
+    }
+}

backend/src/main/java/home/backend/adapters/http/SessionFilter.java

@@ -0,0 +1,45 @@
+package home.backend.adapters.http;
+
+import com.sun.net.httpserver.Filter;
+import com.sun.net.httpserver.HttpExchange;
+import home.backend.adapters.auth.Authentication;
+import home.backend.adapters.auth.Session;
+
+import java.io.IOException;
+import java.util.Map;
+import java.util.Optional;
+
+/** Lets a request through only with a valid session, and hands the user's name on to the handlers. */
+final class SessionFilter extends Filter {
+
+    static final String USER_ATTRIBUTE = "user";
+
+    private final Authentication auth;
+
+    SessionFilter(Authentication auth) {
+        this.auth = auth;
+    }
+
+    @Override
+    public void doFilter(HttpExchange exchange, Chain chain) throws IOException {
+        Optional<Session> session = auth.session(cookies(exchange));
+        if (session.isPresent()) {
+            exchange.setAttribute(USER_ATTRIBUTE, session.get().user());
+            chain.doFilter(exchange);
+        } else {
+            try (exchange) {
+                ApiServer.send(exchange, 401, Map.of("error", "unauthenticated"));
+            }
+        }
+    }
+
+    static String cookies(HttpExchange exchange) {
+        var values = exchange.getRequestHeaders().get("Cookie");
+        return values == null ? null : String.join("; ", values);
+    }
+
+    @Override
+    public String description() {
+        return "session check";
+    }
+}

backend/src/main/java/home/backend/adapters/influx/InfluxAuditRepository.java

@@ -0,0 +1,88 @@
+package home.backend.adapters.influx;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import home.backend.application.AuditRepository;
+
+import java.io.IOException;
+import java.time.Instant;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+/** The gateway's audit measurements (S3) read from InfluxDB; never written. */
+public final class InfluxAuditRepository implements AuditRepository {
+
+    private static final ObjectMapper JSON = new ObjectMapper();
+
+    private final InfluxClient influx;
+
+    public InfluxAuditRepository(InfluxSettings settings) {
+        this.influx = new InfluxClient(settings);
+    }
+
+    @Override
+    public List<Row> heatPump(Instant from, Instant to) throws IOException {
+        return rows("Dom_Pompa", "setpoint_audit", "setpoint", from, to);
+    }
+
+    @Override
+    public List<Row> battery(Instant from, Instant to) throws IOException {
+        return rows("electricity", "deye_settings_audit", "register", from, to);
+    }
+
+    private List<Row> rows(String database, String measurement, String targetTag, Instant from, Instant to)
+            throws IOException {
+        String query = "SELECT * FROM \"" + measurement + "\" WHERE time >= " + from.toEpochMilli()
+                + "ms AND time < " + to.toEpochMilli() + "ms ORDER BY time DESC";
+        var rows = new ArrayList<Row>();
+        for (JsonNode result : results(influx.query(database, query))) {
+            for (JsonNode series : result.path("series")) {
+                for (JsonNode values : series.path("values")) {
+                    rows.add(row(series.path("columns"), values, targetTag));
+                }
+            }
+        }
+        return rows;
+    }
+
+    private static JsonNode results(String body) throws IOException {
+        JsonNode root;
+        try {
+            root = JSON.readTree(body);
+        } catch (JsonProcessingException e) {
+            throw new IOException("InfluxDB returned invalid JSON: " + e.getOriginalMessage(), e);
+        }
+        failOnError(root);
+        for (JsonNode result : root.path("results")) {
+            failOnError(result);
+        }
+        return root.path("results");
+    }
+
+    private static void failOnError(JsonNode node) throws IOException {
+        if (node.hasNonNull("error")) {
+            throw new IOException("InfluxDB query failed: " + node.get("error").asText());
+        }
+    }
+
+    private static Row row(JsonNode columns, JsonNode values, String targetTag) {
+        Map<String, JsonNode> byName = new HashMap<>();
+        for (int i = 0; i < columns.size(); i++) {
+            byName.put(columns.get(i).asText(), values.get(i));
+        }
+        return new Row(Instant.ofEpochMilli(byName.get("time").asLong()), text(byName.get(targetTag)),
+                text(byName.get("requested_by")), text(byName.get("status")),
+                number(byName.get("old_value")), number(byName.get("new_value")));
+    }
+
+    private static String text(JsonNode node) {
+        return node == null || node.isNull() ? "" : node.asText();
+    }
+
+    private static Double number(JsonNode node) {
+        return node == null || !node.isNumber() ? null : node.asDouble();
+    }
+}

backend/src/main/java/home/backend/adapters/influx/InfluxClient.java

@@ -0,0 +1,47 @@
+package home.backend.adapters.influx;
+
+import java.io.IOException;
+import java.net.URI;
+import java.net.URLEncoder;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
+import java.nio.charset.StandardCharsets;
+
+/** Read-only queries to InfluxDB 1.x over its HTTP {@code /query} endpoint; times come back in epoch ms. */
+final class InfluxClient {
+
+    private final InfluxSettings settings;
+    private final HttpClient http;
+
+    InfluxClient(InfluxSettings settings) {
+        this.settings = settings;
+        this.http = HttpClient.newBuilder().connectTimeout(settings.requestTimeout()).build();
+    }
+
+    String query(String database, String query) throws IOException {
+        HttpRequest request = HttpRequest.newBuilder(queryUri(database, query))
+                .timeout(settings.requestTimeout())
+                .GET()
+                .build();
+        try {
+            HttpResponse<String> response = http.send(request, HttpResponse.BodyHandlers.ofString());
+            if (response.statusCode() != 200) {
+                throw new IOException("InfluxDB answered HTTP " + response.statusCode());
+            }
+            return response.body();
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            throw new IOException("InfluxDB request interrupted", e);
+        }
+    }
+
+    private URI queryUri(String database, String query) {
+        String base = settings.baseUri().toString().replaceAll("/+$", "");
+        return URI.create(base + "/query?db=" + encode(database) + "&epoch=ms&q=" + encode(query));
+    }
+
+    private static String encode(String value) {
+        return URLEncoder.encode(value, StandardCharsets.UTF_8);
+    }
+}

backend/src/main/java/home/backend/adapters/influx/InfluxHistoryRepository.java

@@ -0,0 +1,69 @@
+package home.backend.adapters.influx;
+
+import home.backend.application.HeatPumpSamples;
+import home.backend.application.HistoryRepository;
+import home.backend.domain.HeatPumpSample;
+import home.backend.domain.HistoryView.Point;
+import home.backend.domain.Series;
+
+import java.io.IOException;
+import java.time.Duration;
+import java.time.Instant;
+import java.util.List;
+import java.util.Map;
+import java.util.TreeMap;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.Executors;
+
+/** History from InfluxDB 1.x over its HTTP {@code /query} endpoint (ADR-005, ADR-008). */
+public final class InfluxHistoryRepository implements HistoryRepository, HeatPumpSamples {
+
+    private final InfluxClient influx;
+
+    public InfluxHistoryRepository(InfluxSettings settings) {
+        this.influx = new InfluxClient(settings);
+    }
+
+    @Override
+    public List<Point> history(Series series, Instant from, Instant to, int maxPoints) throws IOException {
+        if (maxPoints < 1 || !from.isBefore(to)) {
+            throw new IllegalArgumentException("need maxPoints >= 1 and from < to");
+        }
+        long stepMinutes = stepMinutes(from, to, maxPoints);
+        Map<Long, Double> summed = new TreeMap<>();
+        try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
+            var parts = SeriesSources.of(series).stream()
+                    .map(source -> executor.submit(() -> part(source, from, to, stepMinutes)))
+                    .toList();
+            // Summed in source order, so the result does not depend on which answer comes first.
+            for (var part : parts) {
+                // A part without data is absent, not zero, so a bucket is kept if any part has it.
+                part.get().forEach((t, v) -> summed.merge(t, v, Double::sum));
+            }
+        } catch (ExecutionException e) {
+            throw e.getCause() instanceof IOException io ? io : new IOException(e.getCause());
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            throw new IOException("InfluxDB request interrupted", e);
+        }
+        return summed.entrySet().stream()
+                .map(e -> new Point(Instant.ofEpochMilli(e.getKey()), e.getValue()))
+                .toList();
+    }
+
+    @Override
+    public List<HeatPumpSample> samples(Instant from, Instant to) throws IOException {
+        String query = InfluxSamples.query(from.toEpochMilli(), to.toEpochMilli());
+        return InfluxSamples.parse(influx.query(SeriesSources.LEGACY, query));
+    }
+
+    private Map<Long, Double> part(Source source, Instant from, Instant to, long stepMinutes) throws IOException {
+        String query = source.query(from.toEpochMilli(), to.toEpochMilli(), stepMinutes);
+        return InfluxResponse.parse(influx.query(source.database(), query));
+    }
+
+    private static long stepMinutes(Instant from, Instant to, int maxPoints) {
+        long stepMillis = Math.ceilDiv(Duration.between(from, to).toMillis(), maxPoints);
+        return Math.max(1, Math.ceilDiv(stepMillis, Duration.ofMinutes(1).toMillis()));
+    }
+}

backend/src/main/java/home/backend/adapters/influx/InfluxPvEnergy.java

@@ -0,0 +1,51 @@
+package home.backend.adapters.influx;
+
+import home.backend.application.PvEnergyRepository;
+
+import java.io.IOException;
+import java.time.Instant;
+import java.time.LocalDate;
+import java.time.ZoneId;
+import java.util.Map;
+import java.util.TreeMap;
+
+/** Daily PV energy: the Deye's and the Fronius's own day counters, each read as the day's maximum. */
+public final class InfluxPvEnergy implements PvEnergyRepository {
+
+    private static final ZoneId ZONE = ZoneId.of("Europe/Warsaw");
+    private static final String DATABASE = "electricity";
+
+    private final InfluxClient influx;
+
+    public InfluxPvEnergy(InfluxSettings settings) {
+        this.influx = new InfluxClient(settings);
+    }
+
+    @Override
+    public Map<LocalDate, Double> dailyKwh(LocalDate from, LocalDate to) throws IOException {
+        Map<LocalDate, Double> deye = dailyMax("deye", "pv_today_kwh", from, to);
+        Map<LocalDate, Double> fronius = dailyMax("fronius", "energy_day_wh", from, to);
+        Map<LocalDate, Double> total = new TreeMap<>();
+        deye.forEach((day, kwh) -> {
+            Double wh = fronius.get(day);
+            if (wh != null) {
+                total.put(day, kwh + wh / 1000);
+            }
+        });
+        return total;
+    }
+
+    private Map<LocalDate, Double> dailyMax(String measurement, String field, LocalDate from, LocalDate to)
+            throws IOException {
+        String query = "SELECT max(\"" + field + "\") FROM \"" + measurement + "\" WHERE time >= "
+                + millis(from) + "ms AND time < " + millis(to) + "ms GROUP BY time(1d) fill(none) tz('Europe/Warsaw')";
+        Map<LocalDate, Double> days = new TreeMap<>();
+        InfluxResponse.parse(influx.query(DATABASE, query)).forEach((start, max) ->
+                days.put(Instant.ofEpochMilli(start).atZone(ZONE).toLocalDate(), max));
+        return days;
+    }
+
+    private static long millis(LocalDate day) {
+        return day.atStartOfDay(ZONE).toInstant().toEpochMilli();
+    }
+}

backend/src/main/java/home/backend/adapters/influx/InfluxResponse.java

@@ -0,0 +1,50 @@
+package home.backend.adapters.influx;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+import java.io.IOException;
+import java.util.Map;
+import java.util.TreeMap;
+
+/** The {@code time, mean} rows of an InfluxDB 1.x query response. */
+final class InfluxResponse {
+
+    private static final ObjectMapper JSON = new ObjectMapper();
+
+    private InfluxResponse() {
+    }
+
+    /** Mean per bucket start in epoch milliseconds, ascending; empty when there is no data. */
+    static Map<Long, Double> parse(String body) throws IOException {
+        JsonNode root = read(body);
+        failOnError(root);
+        Map<Long, Double> means = new TreeMap<>();
+        for (JsonNode result : root.path("results")) {
+            failOnError(result);
+            for (JsonNode series : result.path("series")) {
+                for (JsonNode row : series.path("values")) {
+                    if (row.size() >= 2 && row.get(1).isNumber()) {
+                        means.put(row.get(0).asLong(), row.get(1).asDouble());
+                    }
+                }
+            }
+        }
+        return means;
+    }
+
+    private static JsonNode read(String body) throws IOException {
+        try {
+            return JSON.readTree(body);
+        } catch (JsonProcessingException e) {
+            throw new IOException("InfluxDB returned invalid JSON: " + e.getOriginalMessage(), e);
+        }
+    }
+
+    private static void failOnError(JsonNode node) throws IOException {
+        if (node.hasNonNull("error")) {
+            throw new IOException("InfluxDB query failed: " + node.get("error").asText());
+        }
+    }
+}

backend/src/main/java/home/backend/adapters/influx/InfluxSamples.java

@@ -0,0 +1,74 @@
+package home.backend.adapters.influx;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import home.backend.domain.HeatPumpSample;
+import home.backend.domain.HeatPumpView.Setpoints;
+import home.backend.domain.HeatPumpView.Targets;
+import home.backend.domain.Periods;
+
+import java.io.IOException;
+import java.time.Instant;
+import java.util.ArrayList;
+import java.util.List;
+
+/** The raw {@code heat_pump} rows of an InfluxDB 1.x query. */
+final class InfluxSamples {
+
+    private static final ObjectMapper JSON = new ObjectMapper();
+
+    private InfluxSamples() {
+    }
+
+    static String query(long fromMs, long toMs) {
+        return "SELECT output_compressor, output_cwu, output_co, outdoor_temp, cwu_temp,"
+                + " program, target_room_temp, target_cwu_temp, setpoint_co_economy, setpoint_co_comfort,"
+                + " setpoint_cwu_economy, setpoint_cwu_comfort"
+                + " FROM \"heat_pump\" WHERE time >= " + fromMs + "ms AND time < " + toMs + "ms";
+    }
+
+    /** The rows of {@link #query}, as returned (ascending); empty when there is no data. */
+    static List<HeatPumpSample> parse(String body) throws IOException {
+        JsonNode root;
+        try {
+            root = JSON.readTree(body);
+        } catch (JsonProcessingException e) {
+            throw new IOException("InfluxDB returned invalid JSON: " + e.getOriginalMessage(), e);
+        }
+        failOnError(root);
+        List<HeatPumpSample> samples = new ArrayList<>();
+        for (JsonNode result : root.path("results")) {
+            failOnError(result);
+            for (JsonNode series : result.path("series")) {
+                for (JsonNode row : series.path("values")) {
+                    samples.add(new HeatPumpSample(Instant.ofEpochMilli(row.get(0).asLong()),
+                            number(row, 1), number(row, 2), number(row, 3),
+                            number(row, 4), number(row, 5), periods(row)));
+                }
+            }
+        }
+        return samples;
+    }
+
+    private static Periods periods(JsonNode row) {
+        var targets = new Targets(number(row, 7), null, number(row, 8));
+        var setpoints = new Setpoints(whole(row, 9), whole(row, 10), whole(row, 11), whole(row, 12));
+        return Periods.of(whole(row, 6), targets, setpoints);
+    }
+
+    private static Integer whole(JsonNode row, int column) {
+        Double value = number(row, column);
+        return value == null ? null : (int) Math.round(value);
+    }
+
+    private static Double number(JsonNode row, int column) {
+        return row.get(column).isNumber() ? row.get(column).asDouble() : null;
+    }
+
+    private static void failOnError(JsonNode node) throws IOException {
+        if (node.hasNonNull("error")) {
+            throw new IOException("InfluxDB query failed: " + node.get("error").asText());
+        }
+    }
+}

backend/src/main/java/home/backend/adapters/influx/InfluxSettings.java

@@ -0,0 +1,7 @@
+package home.backend.adapters.influx;
+
+import java.net.URI;
+import java.time.Duration;
+
+public record InfluxSettings(URI baseUri, Duration requestTimeout) {
+}

backend/src/main/java/home/backend/adapters/influx/SeriesSources.java

@@ -0,0 +1,44 @@
+package home.backend.adapters.influx;
+
+import home.backend.domain.Series;
+
+import java.util.List;
+import java.util.Map;
+
+/** Where each series lives in InfluxDB. A fixed table: no query is built from user input. */
+final class SeriesSources {
+
+    static final String LEGACY = "Dom_Pompa";
+    private static final String ELECTRICITY = "electricity";
+
+    private static final Map<Series, List<Source>> SOURCES = Map.ofEntries(
+            Map.entry(Series.OUTDOOR_TEMP, List.of(pompa("External temperature"))),
+            Map.entry(Series.INDOOR_TEMP, List.of(pompa("Temp wew"))),
+            Map.entry(Series.CO_BUFFER_TEMP, List.of(pompa("Temp co"))),
+            Map.entry(Series.CWU_TEMP, List.of(pompa("Temp cwu"))),
+            Map.entry(Series.GROUND_IN_TEMP, List.of(pompa("Temp in"))),
+            Map.entry(Series.GROUND_OUT_TEMP, List.of(pompa("Temp out"))),
+            Map.entry(Series.PUMP_OUTLET_TEMP, List.of(pompa("Temp pc out"))),
+            Map.entry(Series.GRID_POWER, List.of(electricity("PRAD2", "total_power_active"))),
+            Map.entry(Series.PV_POWER, List.of(
+                    electricity("deye", "pv1_power_w"),
+                    electricity("deye", "pv2_power_w"),
+                    electricity("fronius", "pv_power_w"))),
+            Map.entry(Series.LOAD_POWER, List.of(electricity("deye", "load_power_w"))),
+            Map.entry(Series.BATTERY_SOC, List.of(electricity("deye", "battery_soc_pct"))));
+
+    private SeriesSources() {
+    }
+
+    static List<Source> of(Series series) {
+        return SOURCES.get(series);
+    }
+
+    private static Source pompa(String field) {
+        return new Source(LEGACY, "POMPA", field);
+    }
+
+    private static Source electricity(String measurement, String field) {
+        return new Source(ELECTRICITY, measurement, field);
+    }
+}

backend/src/main/java/home/backend/adapters/influx/Source.java

@@ -0,0 +1,15 @@
+package home.backend.adapters.influx;
+
+/** One field of one measurement; the parts of a series are summed. */
+record Source(String database, String measurement, String field) {
+
+    String query(long fromMs, long toMs, long stepMinutes) {
+        return "SELECT mean(" + quote(field) + ") FROM " + quote(measurement)
+                + " WHERE time >= " + fromMs + "ms AND time < " + toMs + "ms"
+                + " GROUP BY time(" + stepMinutes + "m) fill(none)";
+    }
+
+    private static String quote(String identifier) {
+        return '"' + identifier.replace("\\", "\\\\").replace("\"", "\\\"") + '"';
+    }
+}

backend/src/main/java/home/backend/adapters/weather/HttpJson.java

@@ -0,0 +1,42 @@
+package home.backend.adapters.weather;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+import java.io.IOException;
+import java.net.URI;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
+import java.time.Duration;
+
+/** GET of a public JSON document, with a timeout on connecting and on the whole request. */
+final class HttpJson {
+
+    private static final ObjectMapper JSON = new ObjectMapper();
+
+    private final HttpClient http;
+    private final Duration timeout;
+
+    HttpJson(Duration timeout) {
+        this.http = HttpClient.newBuilder().connectTimeout(timeout).build();
+        this.timeout = timeout;
+    }
+
+    JsonNode get(URI uri) throws IOException {
+        HttpRequest request = HttpRequest.newBuilder(uri).timeout(timeout).GET().build();
+        try {
+            HttpResponse<String> response = http.send(request, HttpResponse.BodyHandlers.ofString());
+            if (response.statusCode() != 200) {
+                throw new IOException(uri.getHost() + " answered HTTP " + response.statusCode());
+            }
+            return JSON.readTree(response.body());
+        } catch (JsonProcessingException e) {
+            throw new IOException(uri.getHost() + " returned invalid JSON: " + e.getOriginalMessage(), e);
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            throw new IOException("request to " + uri.getHost() + " interrupted", e);
+        }
+    }
+}

backend/src/main/java/home/backend/adapters/weather/ImgwClient.java

@@ -0,0 +1,76 @@
+package home.backend.adapters.weather;
+
+import com.fasterxml.jackson.databind.JsonNode;
+import home.backend.application.WarningSource;
+import home.backend.domain.WeatherView.Warning;
+
+import java.io.IOException;
+import java.net.URI;
+import java.time.DateTimeException;
+import java.time.Duration;
+import java.time.LocalDateTime;
+import java.time.OffsetDateTime;
+import java.time.ZoneId;
+import java.time.format.DateTimeFormatter;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Optional;
+
+/**
+ * IMGW's public list of meteorological warnings, kept to those naming one of our TERYT areas. A warning
+ * that is malformed (no degree or times) is left out rather than failing the others.
+ */
+public final class ImgwClient implements WarningSource {
+
+    private static final ZoneId POLAND = ZoneId.of("Europe/Warsaw");
+    private static final DateTimeFormatter TIME = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
+
+    private final HttpJson http;
+    private final URI uri;
+    private final List<String> teryt;
+
+    public ImgwClient(URI baseUri, WeatherSettings place, Duration timeout) {
+        this.http = new HttpJson(timeout);
+        this.uri = URI.create(baseUri.toString().replaceAll("/+$", "") + "/api/data/warningsmeteo");
+        this.teryt = place.teryt();
+    }
+
+    @Override
+    public List<Warning> warnings() throws IOException {
+        JsonNode root = http.get(uri);
+        if (!root.isArray()) {
+            throw new IOException("IMGW returned no list of warnings");
+        }
+        List<Warning> ours = new ArrayList<>();
+        for (JsonNode item : root) {
+            if (covers(item.path("teryt"))) {
+                warning(item).ifPresent(ours::add);
+            }
+        }
+        return ours;
+    }
+
+    private boolean covers(JsonNode codes) {
+        for (JsonNode code : codes) {
+            if (teryt.contains(code.asText())) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    private static Optional<Warning> warning(JsonNode item) {
+        try {
+            return Optional.of(new Warning(item.path("nazwa_zdarzenia").asText(),
+                    Integer.parseInt(item.path("stopien").asText()),
+                    time(item.path("obowiazuje_od")), time(item.path("obowiazuje_do")),
+                    item.path("tresc").asText()));
+        } catch (NumberFormatException | DateTimeException e) {
+            return Optional.empty();
+        }
+    }
+
+    private static OffsetDateTime time(JsonNode text) {
+        return LocalDateTime.parse(text.asText(), TIME).atZone(POLAND).toOffsetDateTime();
+    }
+}

backend/src/main/java/home/backend/adapters/weather/OpenMeteoClient.java

@@ -0,0 +1,68 @@
+package home.backend.adapters.weather;
+
+import com.fasterxml.jackson.databind.JsonNode;
+import home.backend.application.ForecastSource;
+import home.backend.domain.Forecast;
+import home.backend.domain.Forecast.DailyForecast;
+
+import java.io.IOException;
+import java.net.URI;
+import java.time.DateTimeException;
+import java.time.Duration;
+import java.time.LocalDate;
+import java.util.Map;
+import java.util.TreeMap;
+
+/** Open-Meteo (free, no key): daily values for the past 14 days and the next 4, and the temperature now. */
+public final class OpenMeteoClient implements ForecastSource {
+
+    private static final String DAILY = "weather_code,temperature_2m_max,temperature_2m_min,precipitation_sum,"
+            + "shortwave_radiation_sum,sunshine_duration";
+
+    private final HttpJson http;
+    private final URI uri;
+
+    public OpenMeteoClient(URI baseUri, WeatherSettings place, Duration timeout) {
+        this.http = new HttpJson(timeout);
+        this.uri = URI.create(baseUri.toString().replaceAll("/+$", "") + "/v1/forecast?latitude="
+                + place.latitude() + "&longitude=" + place.longitude() + "&daily=" + DAILY
+                + "&current=temperature_2m&timezone=Europe%2FWarsaw&past_days=14&forecast_days=4");
+    }
+
+    @Override
+    public Forecast forecast() throws IOException {
+        JsonNode root = http.get(uri);
+        JsonNode daily = root.path("daily");
+        JsonNode dates = daily.path("time");
+        if (!dates.isArray() || dates.isEmpty()) {
+            throw new IOException("Open-Meteo returned no daily forecast");
+        }
+        Map<LocalDate, DailyForecast> days = new TreeMap<>();
+        for (int i = 0; i < dates.size(); i++) {
+            days.put(date(dates.get(i).asText()), new DailyForecast(
+                    integer(daily, "weather_code", i), number(daily, "temperature_2m_max", i),
+                    number(daily, "temperature_2m_min", i), number(daily, "precipitation_sum", i),
+                    number(daily, "shortwave_radiation_sum", i), number(daily, "sunshine_duration", i)));
+        }
+        JsonNode now = root.path("current").path("temperature_2m");
+        return new Forecast(now.isNumber() ? now.asDouble() : null, days);
+    }
+
+    private static LocalDate date(String text) throws IOException {
+        try {
+            return LocalDate.parse(text);
+        } catch (DateTimeException e) {
+            throw new IOException("Open-Meteo returned a bad date: " + text, e);
+        }
+    }
+
+    private static Double number(JsonNode daily, String name, int i) {
+        JsonNode value = daily.path(name).path(i);
+        return value.isNumber() ? value.asDouble() : null;
+    }
+
+    private static Integer integer(JsonNode daily, String name, int i) {
+        JsonNode value = daily.path(name).path(i);
+        return value.isNumber() ? value.asInt() : null;
+    }
+}

backend/src/main/java/home/backend/adapters/weather/WeatherSettings.java

@@ -0,0 +1,35 @@
+package home.backend.adapters.weather;
+
+import java.util.List;
+import java.util.Map;
+
+/**
+ * Where the house is and which IMGW areas (TERYT powiat codes) count as ours. Krosno is a city with
+ * powiat rights, 1862; 1807 is the surrounding powiat krośnieński, which warnings may name instead.
+ */
+public record WeatherSettings(double latitude, double longitude, List<String> teryt) {
+
+    public static WeatherSettings fromEnvironment(Map<String, String> env) {
+        return new WeatherSettings(
+                coordinate(env, "WEATHER_LAT", 49.684, 90),
+                coordinate(env, "WEATHER_LON", 21.770, 180),
+                List.of(env.getOrDefault("WEATHER_TERYT", "1862,1807").strip().split("\\s*,\\s*")));
+    }
+
+    private static double coordinate(Map<String, String> env, String name, double fallback, double limit) {
+        String value = env.get(name);
+        if (value == null || value.isBlank()) {
+            return fallback;
+        }
+        try {
+            double number = Double.parseDouble(value.strip());
+            if (Math.abs(number) <= limit) {
+                return number;
+            }
+        } catch (NumberFormatException e) {
+            // reported below with the same message
+        }
+        throw new IllegalArgumentException(name + " must be a number from -" + limit + " to " + limit
+                + ", got: " + value);
+    }
+}

backend/src/main/java/home/backend/application/AuditRepository.java

@@ -0,0 +1,17 @@
+package home.backend.application;
+
+import java.io.IOException;
+import java.time.Instant;
+import java.util.List;
+
+/** The gateway's audit rows in InfluxDB (S3), read only. */
+public interface AuditRepository {
+
+    /** One audited write as recorded; {@code target} is the setpoint name or the Deye register. */
+    record Row(Instant time, String target, String requestedBy, String status, Double oldValue, Double newValue) {
+    }
+
+    List<Row> heatPump(Instant from, Instant to) throws IOException;
+
+    List<Row> battery(Instant from, Instant to) throws IOException;
+}

backend/src/main/java/home/backend/application/AuditService.java

@@ -0,0 +1,70 @@
+package home.backend.application;
+
+import home.backend.application.AuditRepository.Row;
+import home.backend.domain.AuditEntry;
+import home.backend.domain.AuditView;
+
+import java.io.IOException;
+import java.time.Clock;
+import java.time.Duration;
+import java.time.Instant;
+import java.util.Comparator;
+import java.util.Map;
+import java.util.stream.Stream;
+
+/** S3: who changed what and when, from the gateway's audit rows of the heat pump and of the battery. */
+public class AuditService {
+
+    private static final String DEFAULT_RANGE = "7d";
+    private static final Map<String, Duration> RANGES =
+            Map.of("24h", Duration.ofHours(24), "7d", Duration.ofDays(7), "30d", Duration.ofDays(30));
+    private static final Map<String, String> SETPOINTS = Map.of(
+            "cwu_economy", "Ciepła woda – oszczędnie", "cwu_comfort", "Ciepła woda – komfort",
+            "co_economy", "Ogrzewanie – oszczędnie", "co_comfort", "Ogrzewanie – komfort");
+    private static final String RESTORE_USER = "restore";
+    private static final String RESTORE_LABEL = "automatycznie (przywrócenie)";
+
+    private final AuditRepository repository;
+    private final Clock clock;
+
+    public AuditService(AuditRepository repository, Clock clock) {
+        this.repository = repository;
+        this.clock = clock;
+    }
+
+    /**
+     * @param range {@code 24h}, {@code 7d} or {@code 30d}; null means 7d
+     * @throws IllegalArgumentException for an unknown range
+     */
+    public AuditView audit(String range) throws IOException {
+        Duration length = RANGES.get(range == null ? DEFAULT_RANGE : range);
+        if (length == null) {
+            throw new IllegalArgumentException("unknown range: " + range);
+        }
+        Instant to = clock.instant();
+        Instant from = to.minus(length);
+        var heatPump = repository.heatPump(from, to).stream().map(AuditService::heatPumpEntry);
+        var battery = repository.battery(from, to).stream().map(AuditService::batteryEntry);
+        return new AuditView(Stream.concat(heatPump, battery)
+                .sorted(Comparator.comparing(AuditEntry::time).reversed())
+                .toList());
+    }
+
+    private static AuditEntry heatPumpEntry(Row row) {
+        return entry(AuditEntry.HEAT_PUMP, row, SETPOINTS.getOrDefault(row.target(), row.target()), "°C");
+    }
+
+    private static AuditEntry batteryEntry(Row row) {
+        var label = DeyeSettingLabels.of(row.target());
+        return entry(AuditEntry.BATTERY, row, label.what(), label.unit());
+    }
+
+    private static AuditEntry entry(String source, Row row, String what, String unit) {
+        return new AuditEntry(row.time(), source, what, whole(row.oldValue()), whole(row.newValue()), unit,
+                RESTORE_USER.equals(row.requestedBy()) ? RESTORE_LABEL : row.requestedBy(), row.status());
+    }
+
+    private static Integer whole(Double value) {
+        return value == null ? null : (int) Math.round(value);
+    }
+}

backend/src/main/java/home/backend/application/BatteryService.java

@@ -0,0 +1,114 @@
+package home.backend.application;
+
+import home.backend.application.SnapshotFields.Live;
+import home.backend.domain.BatteryChange;
+import home.backend.domain.BatteryResult;
+import home.backend.domain.BatteryView;
+import home.backend.domain.BatteryView.Energy;
+import home.backend.domain.BatteryView.Limits;
+import home.backend.domain.BatteryView.Mode;
+import home.backend.domain.BatteryView.Reserve;
+import home.backend.domain.BatteryView.Slot;
+import home.backend.domain.GatewaySnapshot;
+
+import java.io.IOException;
+import java.time.Clock;
+import java.time.Duration;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.IntStream;
+
+import static home.backend.application.SnapshotFields.on;
+import static home.backend.application.SnapshotFields.whole;
+
+/** F7: the Deye's battery now, and how it is set up. */
+public class BatteryService {
+
+    /** The settings are read every 10 minutes; three missed reads and they are not current. */
+    private static final Duration SETTINGS_MAX_AGE = Duration.ofMinutes(30);
+    private static final int SLOTS = 6;
+    /** The nominal voltage of a 16-cell lithium pack; the Deye reports capacity in Ah only. */
+    private static final double NOMINAL_VOLTS = 51.2;
+
+    private final GatewayClient gateway;
+    private final GatewayBattery battery;
+    private final Clock clock;
+
+    public BatteryService(GatewayClient gateway, GatewayBattery battery, Clock clock) {
+        this.gateway = gateway;
+        this.battery = battery;
+        this.clock = clock;
+    }
+
+    public BatteryResult changeSchedule(BatteryChange change, String user) throws IOException {
+        return battery.changeSchedule(change, user);
+    }
+
+    public BatteryResult changeReserve(int pct, String user) throws IOException {
+        return battery.changeReserve(pct, user);
+    }
+
+    /** Asked on its own: a gateway without battery commands still serves the live view. */
+    private Reserve reserve() {
+        try {
+            return battery.reserve();
+        } catch (IOException e) {
+            return null;
+        }
+    }
+
+    public BatteryView current() throws IOException {
+        GatewaySnapshot snapshot = gateway.snapshot();
+        Live deye = SnapshotFields.live(snapshot, "deye", "deye", clock.instant());
+        Live settings = SnapshotFields.live(snapshot, "deye-settings", "deye_settings", clock.instant(),
+                SETTINGS_MAX_AGE);
+        Map<String, Double> d = deye.fields();
+        Map<String, Double> s = settings.fields();
+        boolean settingsStale = settings.source().stale();
+        Reserve reserve = reserve();
+        return new BatteryView(deye.source().time(), deye.source().stale(),
+                d.get("battery_soc_pct"), d.get("battery_power_w"), d.get("battery_voltage_v"),
+                d.get("battery_current_a"), d.get("battery_temperature_c"), capacityKwh(s),
+                new Energy(d.get("battery_charge_today_kwh"), d.get("battery_discharge_today_kwh")),
+                new Energy(d.get("battery_charge_total_kwh"), d.get("battery_discharge_total_kwh")),
+                settingsStale ? null : mode(s), settingsStale ? List.of() : schedule(s),
+                settingsStale ? null : limits(s), settings.source().time(), settingsStale, reserve, reserve != null);
+    }
+
+    private static Double capacityKwh(Map<String, Double> settings) {
+        Double ah = settings.get("battery_capacity_ah");
+        return ah == null ? null : Math.round(ah * NOMINAL_VOLTS) / 1000.0;
+    }
+
+    private static Mode mode(Map<String, Double> s) {
+        boolean tou = on(s, "tou_enabled");
+        return new Mode(tou, tou ? "Harmonogram: bateria pracuje według przedziałów"
+                : "Rezerwa na awarię: bateria nie rozładowuje się na co dzień");
+    }
+
+    /** Slot n runs from its start to the start of slot n + 1; the last one wraps to the first.
+     * No schedule at all when a start is missing. */
+    private static List<Slot> schedule(Map<String, Double> s) {
+        boolean complete = IntStream.rangeClosed(1, SLOTS).allMatch(n -> whole(s, "prog" + n + "_start_hhmm") != null);
+        if (!complete) {
+            return List.of();
+        }
+        return IntStream.rangeClosed(1, SLOTS).mapToObj(n -> {
+            String prefix = "prog" + n + "_";
+            String next = "prog" + (n % SLOTS + 1) + "_start_hhmm";
+            return new Slot(time(whole(s, prefix + "start_hhmm")), time(whole(s, next)),
+                    whole(s, prefix + "power_w"), whole(s, prefix + "soc_pct"), on(s, prefix + "grid_charge"));
+        }).toList();
+    }
+
+    private static String time(int hhmm) {
+        return "%02d:%02d".formatted(hhmm / 100, hhmm % 100);
+    }
+
+    private static Limits limits(Map<String, Double> s) {
+        return new Limits(whole(s, "max_charge_current_a"), whole(s, "max_discharge_current_a"),
+                whole(s, "shutdown_soc_pct"), whole(s, "low_soc_pct"), whole(s, "restart_soc_pct"),
+                on(s, "grid_charge_enabled"), whole(s, "grid_charge_current_a"),
+                whole(s, "grid_charge_start_soc_pct"));
+    }
+}

backend/src/main/java/home/backend/application/Cached.java

@@ -0,0 +1,80 @@
+package home.backend.application;
+
+import java.io.IOException;
+import java.time.Clock;
+import java.time.Duration;
+import java.time.Instant;
+import java.time.ZoneId;
+
+/**
+ * One remote answer kept for a while, and no longer than its local day when a zone is given. When a refresh
+ * fails the older answer is served marked stale, and the source is left alone for a short back-off so a
+ * source that is down does not make every request wait for its timeout.
+ */
+final class Cached<T> {
+
+    interface Fetch<T> {
+        T fetch() throws IOException;
+    }
+
+    record Entry<T>(T value, boolean stale) {
+    }
+
+    private static final Duration BACK_OFF = Duration.ofSeconds(60);
+
+    private final Duration ttl;
+    private final ZoneId dayZone;
+    private final Clock clock;
+    private final Fetch<T> source;
+    private T value;
+    private Instant fetchedAt;
+    private Instant failedAt;
+
+    Cached(Duration ttl, Clock clock, Fetch<T> source) {
+        this(ttl, null, clock, source);
+    }
+
+    /** @param dayZone the answer expires at midnight of this zone even before the ttl, or null */
+    Cached(Duration ttl, ZoneId dayZone, Clock clock, Fetch<T> source) {
+        this.ttl = ttl;
+        this.dayZone = dayZone;
+        this.clock = clock;
+        this.source = source;
+    }
+
+    /** @throws IOException when the refresh fails or is backing off, and there is nothing older to serve */
+    synchronized Entry<T> get() throws IOException {
+        Instant now = clock.instant();
+        if (value != null && now.isBefore(expiry())) {
+            return new Entry<>(value, false);
+        }
+        if (failedAt != null && now.isBefore(failedAt.plus(BACK_OFF))) {
+            return older(new IOException("source failed recently, not retrying yet"));
+        }
+        try {
+            value = source.fetch();
+            fetchedAt = now;
+            failedAt = null;
+            return new Entry<>(value, false);
+        } catch (IOException e) {
+            failedAt = now;
+            return older(e);
+        }
+    }
+
+    private Entry<T> older(IOException failure) throws IOException {
+        if (value == null) {
+            throw failure;
+        }
+        return new Entry<>(value, true);
+    }
+
+    private Instant expiry() {
+        Instant byTtl = fetchedAt.plus(ttl);
+        if (dayZone == null) {
+            return byTtl;
+        }
+        Instant midnight = fetchedAt.atZone(dayZone).toLocalDate().plusDays(1).atStartOfDay(dayZone).toInstant();
+        return midnight.isBefore(byTtl) ? midnight : byTtl;
+    }
+}

backend/src/main/java/home/backend/application/DayTally.java

@@ -0,0 +1,93 @@
+package home.backend.application;
+
+import home.backend.domain.HeatPumpSample;
+import home.backend.domain.StatsView.Day;
+import home.backend.domain.StatsView.Totals;
+
+import java.time.Duration;
+import java.time.LocalDate;
+
+/** What the heat pump did over some span of polls; days are added up into the totals. */
+final class DayTally {
+
+    private double compressorSeconds;
+    private double cwuSeconds;
+    private double coSeconds;
+    private int starts;
+    private int samples;
+    private double outdoorSum;
+    private int outdoorCount;
+    private Double minCwu;
+    private Double maxCwu;
+
+    void sample(HeatPumpSample s) {
+        samples++;
+        if (s.outdoorTemp() != null) {
+            outdoorSum += s.outdoorTemp();
+            outdoorCount++;
+        }
+        if (s.cwuTemp() != null) {
+            minCwu = lower(minCwu, s.cwuTemp());
+            maxCwu = higher(maxCwu, s.cwuTemp());
+        }
+    }
+
+    /** The outputs of {@code s} held for {@code held}. */
+    void hold(HeatPumpSample s, Duration held) {
+        double seconds = held.toMillis() / 1000.0;
+        compressorSeconds += on(s.compressor()) ? seconds : 0;
+        cwuSeconds += on(s.cwu()) ? seconds : 0;
+        coSeconds += on(s.co()) ? seconds : 0;
+    }
+
+    void start() {
+        starts++;
+    }
+
+    void add(DayTally other) {
+        compressorSeconds += other.compressorSeconds;
+        cwuSeconds += other.cwuSeconds;
+        coSeconds += other.coSeconds;
+        starts += other.starts;
+        samples += other.samples;
+        outdoorSum += other.outdoorSum;
+        outdoorCount += other.outdoorCount;
+        if (other.minCwu != null) {
+            minCwu = lower(minCwu, other.minCwu);
+            maxCwu = higher(maxCwu, other.maxCwu);
+        }
+    }
+
+    Day day(LocalDate date) {
+        if (samples == 0) {
+            return new Day(date, null, null, null, null, null, null, null);
+        }
+        return new Day(date, hours(compressorSeconds), starts, hours(cwuSeconds), hours(coSeconds),
+                avgOutdoor(), minCwu, maxCwu);
+    }
+
+    Totals totals() {
+        return new Totals(hours(compressorSeconds), starts, hours(cwuSeconds), hours(coSeconds),
+                avgOutdoor(), minCwu, maxCwu);
+    }
+
+    static boolean on(Double output) {
+        return output != null && output > 0;
+    }
+
+    private static Double lower(Double known, double value) {
+        return known == null ? value : Math.min(known, value);
+    }
+
+    private static Double higher(Double known, double value) {
+        return known == null ? value : Math.max(known, value);
+    }
+
+    private Double avgOutdoor() {
+        return outdoorCount == 0 ? null : Math.round(outdoorSum / outdoorCount * 10) / 10.0;
+    }
+
+    private static double hours(double seconds) {
+        return Math.round(seconds / 3600 * 100) / 100.0;
+    }
+}

backend/src/main/java/home/backend/application/DeyeSettingLabels.java

@@ -0,0 +1,48 @@
+package home.backend.application;
+
+import java.util.Optional;
+
+/** Polish name and unit of the Deye program registers and of the app's reserve, as the gateway audits them. */
+final class DeyeSettingLabels {
+
+    record Label(String what, String unit) {
+    }
+
+    private static final int TOU_ENABLE = 146;
+    private static final int FIRST_START = 148;
+    private static final int FIRST_SOC = 166;
+    private static final int FIRST_GRID_CHARGE = 172;
+    private static final int SLOTS = 6;
+
+    private DeyeSettingLabels() {
+    }
+
+    static Label of(String register) {
+        if ("reserve".equals(register)) {
+            return new Label("Rezerwa baterii", "%");
+        }
+        int address;
+        try {
+            address = Integer.parseInt(register);
+        } catch (NumberFormatException e) {
+            return unknown(register);
+        }
+        if (address == TOU_ENABLE) {
+            return new Label("Harmonogram baterii", "0/1");
+        }
+        return slot(address, FIRST_START, "start", "HHMM")
+                .or(() -> slot(address, FIRST_SOC, "poziom", "%"))
+                .or(() -> slot(address, FIRST_GRID_CHARGE, "ładowanie z sieci", "0/1"))
+                .orElseGet(() -> unknown(register));
+    }
+
+    private static Label unknown(String register) {
+        return new Label("Rejestr " + register, "");
+    }
+
+    private static Optional<Label> slot(int address, int first, String what, String unit) {
+        return address >= first && address < first + SLOTS
+                ? Optional.of(new Label("Przedział " + (address - first + 1) + ": " + what, unit))
+                : Optional.empty();
+    }
+}

backend/src/main/java/home/backend/application/EnergyDetailsService.java

@@ -0,0 +1,157 @@
+package home.backend.application;
+
+import home.backend.application.SnapshotFields.Live;
+import home.backend.domain.EnergyDetails;
+import home.backend.domain.EnergyDetails.Device;
+import home.backend.domain.EnergyDetails.Group;
+import home.backend.domain.EnergyDetails.Item;
+import home.backend.domain.GatewaySnapshot;
+
+import java.io.IOException;
+import java.time.Clock;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.IntStream;
+
+/**
+ * F7 details: the Deye, Fronius and house meter fields worth a look, grouped and labelled. The
+ * catalog below is the only place that knows a field's label, unit and place; showing a new field
+ * is one line here.
+ */
+public class EnergyDetailsService {
+
+    /** A gateway field shown as {@code label}; {@code scale} turns the stored unit into {@code unit}. */
+    private record Field(String key, String label, String unit, int digits, double scale) {
+    }
+
+    private record Spec(String id, String name, String measurement, List<GroupSpec> groups) {
+    }
+
+    /** {@code measurement} is null for the device's own one. */
+    private record GroupSpec(String title, String measurement, List<Field> fields) {
+    }
+
+    // Each helper returns the fields it stands for, so a group can mix single fields and phase triples.
+    private static Field[] field(String key, String label, String unit, int digits) {
+        return new Field[] {new Field(key, label, unit, digits, 1)};
+    }
+
+    private static Field[] kwhFromWh(String key, String label, int digits) {
+        return new Field[] {new Field(key, label, "kWh", digits, 0.001)};
+    }
+
+    /** L1 to L3 of one quantity; {@code key} holds %d for the phase number. */
+    private static Field[] phases(String key, String label, String unit, int digits) {
+        return IntStream.rangeClosed(1, 3)
+                .mapToObj(n -> new Field(key.formatted(n), label + " L" + n, unit, digits, 1)).toArray(Field[]::new);
+    }
+
+    private static GroupSpec group(String title, Field[]... parts) {
+        return groupOf(null, title, parts);
+    }
+
+    /** A group whose fields come from another measurement of the same device. */
+    private static GroupSpec groupOf(String measurement, String title, Field[]... parts) {
+        return new GroupSpec(title, measurement, Arrays.stream(parts).flatMap(Arrays::stream).toList());
+    }
+
+    private static final List<Spec> CATALOG = List.of(
+            new Spec("deye", "Falownik Deye", "deye", List.of(
+                    group("Bateria",
+                            field("battery_soc_pct", "Naładowanie", "%", 0),
+                            field("battery_power_w", "Moc", "W", 0),
+                            field("battery_voltage_v", "Napięcie", "V", 1),
+                            field("battery_current_a", "Prąd", "A", 1),
+                            field("battery_temperature_c", "Temperatura", "°C", 1)),
+                    group("Sieć",
+                            field("grid_power_w", "Moc razem", "W", 0),
+                            phases("grid_power_l%d_w", "Moc", "W", 0),
+                            phases("grid_voltage_l%d_v", "Napięcie", "V", 1),
+                            field("grid_frequency_hz", "Częstotliwość", "Hz", 2)),
+                    group("Wyjście zapasowe falownika",
+                            field("load_power_w", "Moc razem", "W", 0),
+                            phases("load_power_l%d_w", "Moc", "W", 0)),
+                    group("Panele PV",
+                            field("pv1_power_w", "PV1 moc", "W", 0),
+                            field("pv1_voltage_v", "PV1 napięcie", "V", 1),
+                            field("pv1_current_a", "PV1 prąd", "A", 1),
+                            field("pv2_power_w", "PV2 moc", "W", 0),
+                            field("pv2_voltage_v", "PV2 napięcie", "V", 1),
+                            field("pv2_current_a", "PV2 prąd", "A", 1)),
+                    group("Dziś",
+                            field("pv_today_kwh", "Produkcja PV", "kWh", 1),
+                            field("load_today_kwh", "Wyjście zapasowe", "kWh", 1),
+                            field("grid_bought_today_kwh", "Pobrano z sieci", "kWh", 1),
+                            field("grid_sold_today_kwh", "Oddano do sieci", "kWh", 1),
+                            field("battery_charge_today_kwh", "Bateria naładowana", "kWh", 1),
+                            field("battery_discharge_today_kwh", "Bateria rozładowana", "kWh", 1)),
+                    group("Od początku",
+                            field("pv_total_kwh", "Produkcja PV", "kWh", 0),
+                            field("load_total_kwh", "Wyjście zapasowe", "kWh", 0),
+                            field("grid_bought_total_kwh", "Pobrano z sieci", "kWh", 0),
+                            field("grid_sold_total_kwh", "Oddano do sieci", "kWh", 0),
+                            field("battery_charge_total_kwh", "Bateria naładowana", "kWh", 0),
+                            field("battery_discharge_total_kwh", "Bateria rozładowana", "kWh", 0)),
+                    group("Falownik",
+                            field("inverter_power_w", "Moc wyjściowa", "W", 0),
+                            field("inverter_temperature_c", "Temperatura", "°C", 1),
+                            field("heatsink_temperature_c", "Radiator", "°C", 1)))),
+            new Spec("fronius", "Falownik Fronius", "fronius", List.of(
+                    group("Teraz", field("pv_power_w", "Moc PV", "W", 0)),
+                    group("Produkcja",
+                            kwhFromWh("energy_day_wh", "Dziś", 1),
+                            kwhFromWh("energy_year_wh", "Ten rok", 0),
+                            kwhFromWh("energy_total_wh", "Od początku", 0)))),
+            new Spec("house-meter", "Licznik domu", "PRAD2", List.of(
+                    group("Moc czynna",
+                            field("total_power_active", "Razem", "W", 0),
+                            phases("p%d_power_active", "Moc", "W", 0)),
+                    group("Napięcie", phases("p%d_voltage", "Napięcie", "V", 1)),
+                    group("Prąd", phases("p%d_current", "Prąd", "A", 2)),
+                    group("Współczynnik mocy", phases("p%d_power_factor", "cos φ", "", 2)),
+                    group("Sieć", field("frequency", "Częstotliwość", "Hz", 2)),
+                    group("Energia od początku",
+                            field("import_energy_active", "Pobrana", "kWh", 0),
+                            field("export_energy_active", "Oddana", "kWh", 0)),
+                    groupOf("house_meter_phases", "Energia na fazę",
+                            phases("l%d_import_energy_active_kwh", "Pobrana", "kWh", 0),
+                            phases("l%d_export_energy_active_kwh", "Oddana", "kWh", 0)))));
+
+    private final GatewayClient gateway;
+    private final Clock clock;
+
+    public EnergyDetailsService(GatewayClient gateway, Clock clock) {
+        this.gateway = gateway;
+        this.clock = clock;
+    }
+
+    public EnergyDetails current() throws IOException {
+        GatewaySnapshot snapshot = gateway.snapshot();
+        return new EnergyDetails(CATALOG.stream().map(spec -> device(spec, snapshot)).toList());
+    }
+
+    private Device device(Spec spec, GatewaySnapshot snapshot) {
+        Live live = SnapshotFields.live(snapshot, spec.id(), spec.measurement(), clock.instant());
+        List<Group> groups = spec.groups().stream()
+                .map(g -> group(g, g.measurement() == null ? live.fields() : fieldsOf(snapshot, spec.id(), g)))
+                .filter(g -> !g.items().isEmpty()).toList();
+        return new Device(spec.id(), spec.name(), live.source().time(), live.source().stale(), groups);
+    }
+
+    private Map<String, Double> fieldsOf(GatewaySnapshot snapshot, String device, GroupSpec group) {
+        return SnapshotFields.live(snapshot, device, group.measurement(), clock.instant()).fields();
+    }
+
+    private static Group group(GroupSpec spec, Map<String, Double> fields) {
+        List<Item> items = spec.fields().stream().filter(f -> fields.containsKey(f.key()))
+                .map(f -> new Item(f.label(), scaled(fields.get(f.key()), f), f.unit(), f.digits())).toList();
+        return new Group(spec.title(), items);
+    }
+
+    /** Rounded to the shown precision, so a conversion leaves no binary noise such as 4.3999999. */
+    private static double scaled(double value, Field f) {
+        double factor = Math.pow(10, f.digits());
+        return Math.round(value * f.scale() * factor) / factor;
+    }
+}

backend/src/main/java/home/backend/application/EnergyService.java

@@ -0,0 +1,93 @@
+package home.backend.application;
+
+import home.backend.application.SnapshotFields.Live;
+import home.backend.domain.EnergyView;
+import home.backend.domain.EnergyView.Source;
+import home.backend.domain.EnergyView.Today;
+import home.backend.domain.GatewaySnapshot;
+
+import java.io.IOException;
+import java.time.Clock;
+import java.time.Instant;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.stream.Stream;
+
+/**
+ * F7: house electricity from the Deye inverter, the Fronius PV inverter and the house meter.
+ * The Deye "load" registers cover only its backup output, so the house is a balance:
+ * <ul>
+ * <li>now = Deye PV1 + PV2 + Fronius PV + Deye battery (+discharge, − charge) + grid, where grid is the
+ * house meter's total active power when it is live, else the Deye's grid power; floored at 0, null when
+ * any of those readings is missing or stale;</li>
+ * <li>today = Deye PV + Fronius day energy + grid bought − grid sold + battery discharged − battery charged
+ * (Deye day counters), null when any is missing.</li>
+ * </ul>
+ */
+public class EnergyService {
+
+    private final GatewayClient gateway;
+    private final Clock clock;
+
+    public EnergyService(GatewayClient gateway, Clock clock) {
+        this.gateway = gateway;
+        this.clock = clock;
+    }
+
+    public EnergyView current() throws IOException {
+        GatewaySnapshot snapshot = gateway.snapshot();
+        Live deye = SnapshotFields.live(snapshot, "deye", "deye", clock.instant());
+        Live fronius = SnapshotFields.live(snapshot, "fronius", "fronius", clock.instant());
+        Map<String, Double> d = deye.fields();
+        Map<String, Double> f = fronius.fields();
+        Map<String, Double> meter = SnapshotFields.live(snapshot, "house-meter", "PRAD2", clock.instant()).fields();
+
+        Double froniusKwh = f.containsKey("energy_day_wh") ? f.get("energy_day_wh") / 1000 : null;
+        Today today = new Today(round(sum(d.get("pv_today_kwh"), froniusKwh)),
+                d.get("grid_bought_today_kwh"), d.get("grid_sold_today_kwh"), houseKwh(d, froniusKwh));
+        List<Source> sources = List.of(deye.source(), fronius.source());
+        return new EnergyView(oldest(sources), sources,
+                sum(d.get("pv1_power_w"), d.get("pv2_power_w"), f.get("pv_power_w")),
+                d.get("grid_power_w"), d.get("battery_power_w"), d.get("battery_soc_pct"),
+                housePowerW(d, f, meter.getOrDefault("total_power_active", d.get("grid_power_w"))),
+                d.get("load_power_w"), today);
+    }
+
+    private static Double housePowerW(Map<String, Double> deye, Map<String, Double> fronius, Double gridW) {
+        Double pv1 = deye.get("pv1_power_w");
+        Double pv2 = deye.get("pv2_power_w");
+        Double pvFronius = fronius.get("pv_power_w");
+        Double battery = deye.get("battery_power_w");
+        if (Stream.of(pv1, pv2, pvFronius, battery, gridW).anyMatch(Objects::isNull)) {
+            return null;
+        }
+        return Math.max(0, pv1 + pv2 + pvFronius + battery + gridW);
+    }
+
+    private static Double houseKwh(Map<String, Double> deye, Double froniusKwh) {
+        Double pv = deye.get("pv_today_kwh");
+        Double bought = deye.get("grid_bought_today_kwh");
+        Double sold = deye.get("grid_sold_today_kwh");
+        Double discharged = deye.get("battery_discharge_today_kwh");
+        Double charged = deye.get("battery_charge_today_kwh");
+        if (Stream.of(pv, froniusKwh, bought, sold, discharged, charged).anyMatch(Objects::isNull)) {
+            return null;
+        }
+        return round(Math.max(0, pv + froniusKwh + bought - sold + discharged - charged));
+    }
+
+    private static Instant oldest(List<Source> sources) {
+        return sources.stream().map(Source::time).flatMap(Stream::ofNullable).min(Instant::compareTo).orElse(null);
+    }
+
+    /** Sum of the values that exist; null when none does. */
+    private static Double sum(Double... values) {
+        return Stream.of(values).filter(v -> v != null).reduce(Double::sum).orElse(null);
+    }
+
+    /** Wh to kWh leaves binary noise such as 34.300000000000004. */
+    private static Double round(Double kwh) {
+        return kwh == null ? null : Math.round(kwh * 1000) / 1000.0;
+    }
+}

backend/src/main/java/home/backend/application/ForecastSource.java

@@ -0,0 +1,11 @@
+package home.backend.application;
+
+import home.backend.domain.Forecast;
+
+import java.io.IOException;
+
+/** The weather forecast service: the past 14 days and the next 3. */
+public interface ForecastSource {
+
+    Forecast forecast() throws IOException;
+}

backend/src/main/java/home/backend/application/GatewayBattery.java

@@ -0,0 +1,19 @@
+package home.backend.application;
+
+import home.backend.domain.BatteryChange;
+import home.backend.domain.BatteryResult;
+import home.backend.domain.BatteryView.Reserve;
+
+import java.io.IOException;
+
+/** Battery settings through the gateway, which checks every change (ADR-013). */
+public interface GatewayBattery {
+
+    /** @throws IOException when the gateway has no battery commands, or cannot be reached */
+    Reserve reserve() throws IOException;
+
+    /** A verdict, even a negative one; IOException only when no verdict could be obtained. */
+    BatteryResult changeSchedule(BatteryChange change, String requestedBy) throws IOException;
+
+    BatteryResult changeReserve(int pct, String requestedBy) throws IOException;
+}

backend/src/main/java/home/backend/application/GatewayClient.java

@@ -0,0 +1,11 @@
+package home.backend.application;
+
+import home.backend.domain.GatewaySnapshot;
+
+import java.io.IOException;
+
+/** The live state, read from the gateway on the Pi through the tunnel. */
+public interface GatewayClient {
+
+    GatewaySnapshot snapshot() throws IOException;
+}

backend/src/main/java/home/backend/application/GatewayCommands.java

@@ -0,0 +1,23 @@
+package home.backend.application;
+
+import home.backend.domain.Command;
+import home.backend.domain.CommandResult;
+import home.backend.domain.RestoreResult;
+import home.backend.domain.SetpointState;
+
+import java.io.IOException;
+
+/** The only way the backend writes anything: through the gateway, which checks every command. */
+public interface GatewayCommands {
+
+    /** A verdict, even a negative one; IOException only when no verdict could be obtained. */
+    CommandResult apply(Command command) throws IOException;
+
+    /** Ends the pending change of a setpoint now; a verdict like {@link #apply}. */
+    RestoreResult restore(String setpoint, String requestedBy) throws IOException;
+
+    SetpointState setpoints() throws IOException;
+
+    /** Keeps the gateway's live restores alive; returns how many it extended. */
+    int renewLeases() throws IOException;
+}

backend/src/main/java/home/backend/application/GatewayRefresh.java

@@ -0,0 +1,11 @@
+package home.backend.application;
+
+import home.backend.domain.RefreshResult;
+
+import java.io.IOException;
+
+/** Asks the gateway for fresh readings; it decides which devices may be polled again yet. */
+public interface GatewayRefresh {
+
+    RefreshResult refresh() throws IOException;
+}

backend/src/main/java/home/backend/application/HealthService.java

@@ -0,0 +1,38 @@
+package home.backend.application;
+
+import home.backend.domain.GatewaySnapshot;
+import home.backend.domain.GatewaySnapshot.DeviceSnapshot;
+import home.backend.domain.HealthView;
+import home.backend.domain.HealthView.DeviceHealth;
+
+import java.io.IOException;
+import java.time.Clock;
+import java.util.List;
+
+/** F5: whether the gateway answers and which device links are up. */
+public class HealthService {
+
+    private final GatewayClient gateway;
+    private final Clock clock;
+    private final String version;
+
+    public HealthService(GatewayClient gateway, Clock clock, String version) {
+        this.gateway = gateway;
+        this.clock = clock;
+        this.version = version;
+    }
+
+    public HealthView current() {
+        try {
+            GatewaySnapshot snapshot = gateway.snapshot();
+            List<DeviceHealth> devices = snapshot.devices().stream().map(HealthService::health).toList();
+            return new HealthView(clock.instant(), true, devices, version, snapshot.version());
+        } catch (IOException e) {
+            return new HealthView(clock.instant(), false, List.of(), version, null);
+        }
+    }
+
+    private static DeviceHealth health(DeviceSnapshot d) {
+        return new DeviceHealth(d.name(), d.up(), d.lastSuccess(), d.lastError());
+    }
+}

backend/src/main/java/home/backend/application/HeatPumpSamples.java

@@ -0,0 +1,13 @@
+package home.backend.application;
+
+import home.backend.domain.HeatPumpSample;
+
+import java.io.IOException;
+import java.time.Instant;
+import java.util.List;
+
+/** The heat pump polls stored in InfluxDB, oldest first. */
+public interface HeatPumpSamples {
+
+    List<HeatPumpSample> samples(Instant from, Instant to) throws IOException;
+}

backend/src/main/java/home/backend/application/HeatPumpService.java

@@ -0,0 +1,89 @@
+package home.backend.application;
+
+import home.backend.domain.GatewaySnapshot;
+import home.backend.domain.GatewaySnapshot.Measurement;
+import home.backend.domain.HeatPumpView;
+import home.backend.domain.HeatPumpView.Pumps;
+import home.backend.domain.HeatPumpView.Setpoints;
+import home.backend.domain.HeatPumpView.State;
+import home.backend.domain.HeatPumpView.Targets;
+import home.backend.domain.HeatPumpView.Temperatures;
+import home.backend.domain.Periods;
+
+import java.io.IOException;
+import java.time.Clock;
+import java.time.Instant;
+import java.util.Map;
+import java.util.Optional;
+
+import static home.backend.application.SnapshotFields.on;
+import static home.backend.application.SnapshotFields.whole;
+
+/** F1: the heat pump's live state from the gateway's {@code heat_pump} measurement. */
+public class HeatPumpService {
+
+    private static final String DATABASE = "Dom_Pompa";
+    private static final State[] STATES = State.values();
+
+    private final GatewayClient gateway;
+    private final Clock clock;
+
+    public HeatPumpService(GatewayClient gateway, Clock clock) {
+        this.gateway = gateway;
+        this.clock = clock;
+    }
+
+    public HeatPumpView current() throws IOException {
+        GatewaySnapshot snapshot = gateway.snapshot();
+        Optional<Measurement> reading = SnapshotFields.find(snapshot, "heat-pump", "heat_pump")
+                .filter(m -> DATABASE.equals(m.database()));
+        boolean stale = SnapshotFields.stale(SnapshotFields.device(snapshot, "heat-pump"), reading, clock.instant());
+        return view(reading.map(Measurement::time).orElse(null), stale,
+                reading.map(Measurement::fields).orElse(Map.of()));
+    }
+
+    private static HeatPumpView view(Instant time, boolean stale, Map<String, Double> f) {
+        Integer alarmCode = whole(f, "alarm_code");
+        var targets = new Targets(tenths(f, "target_room_temp"), tenths(f, "target_co_temp"),
+                tenths(f, "target_cwu_temp"));
+        var setpoints = new Setpoints(whole(f, "setpoint_co_economy"), whole(f, "setpoint_co_comfort"),
+                whole(f, "setpoint_cwu_economy"), whole(f, "setpoint_cwu_comfort"));
+        return new HeatPumpView(time, stale, state(f), whole(f, "output_compressor"),
+                on(f, "alarm") || on(f, "alarm_code"), alarmCode, alarmText(alarmCode),
+                new Pumps(on(f, "output_co"), on(f, "output_buffer"), on(f, "output_circulation"),
+                        on(f, "output_ground"), on(f, "output_cwu")),
+                new Temperatures(tenths(f, "outdoor_temp"), tenths(f, "indoor_temp"),
+                        tenths(f, "co_buffer_temp"), tenths(f, "cwu_temp"), tenths(f, "ground_in_temp"),
+                        tenths(f, "ground_out_temp"), tenths(f, "pump_outlet_temp"),
+                        tenths(f, "outdoor_avg_temp")),
+                targets, setpoints, Periods.of(whole(f, "program"), targets, setpoints));
+    }
+
+    /** Codes of register 4011 as the vendor app names them; unverified on our device. */
+    private static String alarmText(Integer code) {
+        if (code == null || code == 0) {
+            return null;
+        }
+        return switch (code) {
+            case 2 -> "Usterka czujnika temperatury zewnętrznej";
+            case 3 -> "Usterka czujnika temperatury CO";
+            case 4 -> "Usterka czujnika temperatury wewnętrznej";
+            case 5 -> "Usterka czujnika temperatury CWU";
+            case 14 -> "Usterka czujnika temperatury wyjścia pompy";
+            case 15 -> "Usterka czujnika temperatury dolnego źródła";
+            case 1003 -> "Zadziałał presostat (ciśnienie)";
+            default -> "Kod usterki " + code;
+        };
+    }
+
+    /** The controller resolves 0.1 °C; the gateway's 212 * 0.1 is 21.200000000000003. */
+    private static Double tenths(Map<String, Double> fields, String name) {
+        Double value = fields.get(name);
+        return value == null ? null : Math.round(value * 10) / 10.0;
+    }
+
+    private static State state(Map<String, Double> f) {
+        Integer mode = whole(f, "pump_mode");
+        return mode == null || mode < 0 || mode >= STATES.length ? null : STATES[mode];
+    }
+}

backend/src/main/java/home/backend/application/HistoryRepository.java

@@ -0,0 +1,14 @@
+package home.backend.application;
+
+import home.backend.domain.HistoryView.Point;
+import home.backend.domain.Series;
+
+import java.io.IOException;
+import java.time.Instant;
+import java.util.List;
+
+/** Past values from InfluxDB, averaged into about {@code maxPoints} steps. */
+public interface HistoryRepository {
+
+    List<Point> history(Series series, Instant from, Instant to, int maxPoints) throws IOException;
+}

backend/src/main/java/home/backend/application/HistoryService.java

@@ -0,0 +1,43 @@
+package home.backend.application;
+
+import home.backend.domain.HistoryView;
+import home.backend.domain.Series;
+
+import java.io.IOException;
+import java.time.Clock;
+import java.time.Duration;
+import java.time.Instant;
+import java.util.Map;
+
+/** F2: one series over the last 24 hours or 7 days. */
+public class HistoryService {
+
+    static final int MAX_POINTS = 300;
+    private static final String DEFAULT_RANGE = "24h";
+    private static final Map<String, Duration> RANGES =
+            Map.of("24h", Duration.ofHours(24), "7d", Duration.ofDays(7));
+
+    private final HistoryRepository repository;
+    private final Clock clock;
+
+    public HistoryService(HistoryRepository repository, Clock clock) {
+        this.repository = repository;
+        this.clock = clock;
+    }
+
+    /**
+     * @param range {@code 24h} or {@code 7d}; null means 24h
+     * @throws IllegalArgumentException for an unknown series or range
+     */
+    public HistoryView history(String seriesId, String range) throws IOException {
+        Series series = Series.fromId(seriesId)
+                .orElseThrow(() -> new IllegalArgumentException("unknown series: " + seriesId));
+        Duration length = RANGES.get(range == null ? DEFAULT_RANGE : range);
+        if (length == null) {
+            throw new IllegalArgumentException("unknown range: " + range);
+        }
+        Instant to = clock.instant();
+        return new HistoryView(series.id(), series.unit(),
+                repository.history(series, to.minus(length), to, MAX_POINTS));
+    }
+}

backend/src/main/java/home/backend/application/LeaseRenewer.java

@@ -0,0 +1,53 @@
+package home.backend.application;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+import java.time.Duration;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Tells the gateway now and then that we are still here (ADR-011): while it hears us, our setpoint
+ * changes stay; once we or the tunnel are gone for 15 minutes, it restores them on its own.
+ */
+public class LeaseRenewer implements AutoCloseable {
+
+    /** A third of the gateway's lease, so two renewals in a row may fail. */
+    public static final Duration PERIOD = Duration.ofMinutes(5);
+
+    private static final Logger LOGGER = LoggerFactory.getLogger(LeaseRenewer.class);
+
+    private final GatewayCommands gateway;
+    private final ScheduledExecutorService scheduler = Executors.newSingleThreadScheduledExecutor(
+            Thread.ofVirtual().name("lease-renewal").factory());
+
+    public LeaseRenewer(GatewayCommands gateway) {
+        this.gateway = gateway;
+    }
+
+    public void start() {
+        start(PERIOD);
+    }
+
+    void start(Duration period) {
+        scheduler.scheduleWithFixedDelay(this::renew, 0, period.toMillis(), TimeUnit.MILLISECONDS);
+    }
+
+    /** A failure is logged and retried next cycle; an exception would end the schedule for good. */
+    void renew() {
+        try {
+            int renewed = gateway.renewLeases();
+            LOGGER.debug("renewed {} lease(s)", renewed);
+        } catch (IOException | RuntimeException e) {
+            LOGGER.warn("could not renew the gateway leases, retrying in {}: {}", PERIOD, e.toString());
+        }
+    }
+
+    @Override
+    public void close() {
+        scheduler.shutdownNow();
+    }
+}

backend/src/main/java/home/backend/application/PiSensorService.java

@@ -0,0 +1,27 @@
+package home.backend.application;
+
+import home.backend.application.SnapshotFields.Live;
+import home.backend.domain.PiSensorView;
+
+import java.io.IOException;
+import java.time.Clock;
+import java.util.Map;
+
+/** The BME280 on the Pi, read by the gateway every 5 minutes. */
+public class PiSensorService {
+
+    private final GatewayClient gateway;
+    private final Clock clock;
+
+    public PiSensorService(GatewayClient gateway, Clock clock) {
+        this.gateway = gateway;
+        this.clock = clock;
+    }
+
+    public PiSensorView current() throws IOException {
+        Live live = SnapshotFields.live(gateway.snapshot(), "bme280", "MEASUREMENT", clock.instant());
+        Map<String, Double> f = live.fields();
+        return new PiSensorView(live.source().time(), live.source().stale(),
+                f.get("temperature"), f.get("humidity"), f.get("pressure"));
+    }
+}

backend/src/main/java/home/backend/application/ProgramService.java

@@ -0,0 +1,193 @@
+package home.backend.application;
+
+import home.backend.domain.HeatPumpSample;
+import home.backend.domain.Period;
+import home.backend.domain.Periods;
+import home.backend.domain.ProgramView;
+import home.backend.domain.ProgramView.Circuit;
+import home.backend.domain.ProgramView.Confidence;
+import home.backend.domain.ProgramView.Interval;
+import home.backend.domain.ProgramView.Weekday;
+
+import java.io.IOException;
+import java.time.Clock;
+import java.time.Duration;
+import java.time.Instant;
+import java.time.LocalDate;
+import java.time.LocalDateTime;
+import java.time.temporal.ChronoUnit;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.TreeMap;
+import java.util.TreeSet;
+import java.util.function.Function;
+
+/**
+ * F6: the weekly program as the history shows it, without asking the controller (its program
+ * registers sit behind a shared selector, so reading them would mean writing). A transition between
+ * two adjacent polls, economy to comfort or back, puts a comfort boundary halfway between them; a
+ * poll in another period (override, or setpoints that make the periods ambiguous, for instance while
+ * we write one) breaks the chain, as does a gap in the data. Times are local, so a day with a change
+ * of time needs no special case. Today is left out: it is not over.
+ */
+public class ProgramService {
+
+    private static final int DEFAULT_DAYS = 14;
+    private static final int MIN_DAYS = 7;
+    private static final int MAX_DAYS = 30;
+    private static final Duration MAX_GAP = StatsService.MAX_HOLD;
+    private static final int STEP_MINUTES = 5;
+    private static final int MINUTES_PER_DAY = 24 * 60;
+
+    private record Span(int from, int to) {
+    }
+
+    /** What the history says about one circuit: days with a known period and their comfort spans. */
+    private record Observed(Set<LocalDate> days, Map<LocalDate, List<Span>> comfort) {
+    }
+
+    private final HeatPumpSamples repository;
+    private final Clock clock;
+
+    public ProgramService(HeatPumpSamples repository, Clock clock) {
+        this.repository = repository;
+        this.clock = clock;
+    }
+
+    /**
+     * @param days how many past days to read, 7 to 30; null means 14
+     * @throws IllegalArgumentException for anything else
+     */
+    public ProgramView program(String days) throws IOException {
+        int length = length(days);
+        LocalDate today = clock.instant().atZone(StatsService.ZONE).toLocalDate();
+        List<HeatPumpSample> samples = repository.samples(
+                today.minusDays(length).atStartOfDay(StatsService.ZONE).toInstant(),
+                today.atStartOfDay(StatsService.ZONE).toInstant());
+        Observed cwu = observe(samples, Periods::cwu);
+        Observed room = observe(samples, Periods::room);
+        List<Weekday> weekdays = new ArrayList<>();
+        for (int day = 1; day <= 7; day++) {
+            weekdays.add(new Weekday(day, circuit(cwu, day), circuit(room, day)));
+        }
+        return new ProgramView(length, weekdays);
+    }
+
+    private static int length(String days) {
+        if (days == null) {
+            return DEFAULT_DAYS;
+        }
+        try {
+            int length = Integer.parseInt(days);
+            if (length >= MIN_DAYS && length <= MAX_DAYS) {
+                return length;
+            }
+        } catch (NumberFormatException e) {
+            // reported below
+        }
+        throw new IllegalArgumentException("days must be " + MIN_DAYS + " to " + MAX_DAYS);
+    }
+
+    private static Observed observe(List<HeatPumpSample> samples, Function<Periods, Period> circuit) {
+        Set<LocalDate> days = new TreeSet<>();
+        Map<LocalDate, List<Span>> comfort = new TreeMap<>();
+        Period previous = null;
+        Instant previousTime = null;
+        Instant comfortStart = null;
+        for (HeatPumpSample sample : samples) {
+            Period period = circuit.apply(sample.periods());
+            if (period != Period.COMFORT && period != Period.ECONOMY) {
+                previous = null;
+                comfortStart = null;
+                continue;
+            }
+            days.add(sample.t().atZone(StatsService.ZONE).toLocalDate());
+            boolean adjacent = previous != null && Duration.between(previousTime, sample.t()).compareTo(MAX_GAP) <= 0;
+            if (!adjacent) {
+                comfortStart = null;
+            } else if (period != previous) {
+                Instant boundary = previousTime.plus(Duration.between(previousTime, sample.t()).dividedBy(2));
+                if (period == Period.COMFORT) {
+                    comfortStart = boundary;
+                } else if (comfortStart != null) {
+                    addSpans(comfort, comfortStart, boundary);
+                    comfortStart = null;
+                }
+            }
+            previous = period;
+            previousTime = sample.t();
+        }
+        return new Observed(days, comfort);
+    }
+
+    /** Splits at local midnight; a start at 23:58 and an end at 00:03 are rounded before that. */
+    private static void addSpans(Map<LocalDate, List<Span>> comfort, Instant from, Instant to) {
+        LocalDateTime start = rounded(from.atZone(StatsService.ZONE).toLocalDateTime());
+        LocalDateTime end = rounded(to.atZone(StatsService.ZONE).toLocalDateTime());
+        for (LocalDate date = start.toLocalDate(); !date.isAfter(end.toLocalDate()); date = date.plusDays(1)) {
+            int spanStart = date.equals(start.toLocalDate()) ? minutes(start) : 0;
+            int spanEnd = date.equals(end.toLocalDate()) ? minutes(end) : MINUTES_PER_DAY;
+            if (spanEnd > spanStart) {
+                comfort.computeIfAbsent(date, d -> new ArrayList<>()).add(new Span(spanStart, spanEnd));
+            }
+        }
+    }
+
+    private static LocalDateTime rounded(LocalDateTime time) {
+        long steps = Math.round((time.getMinute() * 60 + time.getSecond()) / (STEP_MINUTES * 60.0));
+        return time.truncatedTo(ChronoUnit.HOURS).plusMinutes(steps * STEP_MINUTES);
+    }
+
+    private static int minutes(LocalDateTime time) {
+        return time.getHour() * 60 + time.getMinute();
+    }
+
+    /**
+     * The pattern most days of this weekday agree on (the latest wins a tie); {@code CONFIRMED} when at
+     * least two days show it.
+     */
+    private static Circuit circuit(Observed observed, int weekday) {
+        List<List<Span>> patterns = observed.days().stream()
+                .filter(date -> date.getDayOfWeek().getValue() == weekday)
+                .map(date -> observed.comfort().getOrDefault(date, List.of()))
+                .toList();
+        if (patterns.isEmpty()) {
+            return new Circuit(Confidence.NO_DATA, 0, 0, List.of());
+        }
+        List<Span> best = null;
+        int bestCount = 0;
+        for (List<Span> pattern : patterns) {
+            int count = (int) patterns.stream().filter(other -> agree(pattern, other)).count();
+            if (count >= bestCount) {
+                best = pattern;
+                bestCount = count;
+            }
+        }
+        return new Circuit(bestCount >= 2 ? Confidence.CONFIRMED : Confidence.SEEN_ONCE, patterns.size(), bestCount,
+                best.stream().map(ProgramService::interval).toList());
+    }
+
+    /** Equal within one step at both ends of every span. */
+    private static boolean agree(List<Span> a, List<Span> b) {
+        if (a.size() != b.size()) {
+            return false;
+        }
+        for (int i = 0; i < a.size(); i++) {
+            if (Math.abs(a.get(i).from() - b.get(i).from()) > STEP_MINUTES
+                    || Math.abs(a.get(i).to() - b.get(i).to()) > STEP_MINUTES) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    private static Interval interval(Span span) {
+        return new Interval(hhmm(span.from()), hhmm(span.to()));
+    }
+
+    private static String hhmm(int minutes) {
+        return String.format("%02d:%02d", minutes / 60, minutes % 60);
+    }
+}

backend/src/main/java/home/backend/application/PvEnergyRepository.java

@@ -0,0 +1,12 @@
+package home.backend.application;
+
+import java.io.IOException;
+import java.time.LocalDate;
+import java.util.Map;
+
+/** What the panels produced, from InfluxDB. */
+public interface PvEnergyRepository {
+
+    /** Deye plus Fronius kWh per local day from {@code from} up to {@code to}; days missing either are absent. */
+    Map<LocalDate, Double> dailyKwh(LocalDate from, LocalDate to) throws IOException;
+}

backend/src/main/java/home/backend/application/SetpointService.java

@@ -0,0 +1,178 @@
+package home.backend.application;
+
+import home.backend.domain.Command;
+import home.backend.domain.CommandResult;
+import home.backend.domain.Preset;
+import home.backend.domain.Preset.Change;
+import home.backend.domain.PresetResult;
+import home.backend.domain.PresetResult.ChangeResult;
+import home.backend.domain.PresetResult.ChangeStatus;
+import home.backend.domain.RestoreResult;
+import home.backend.domain.Setpoint;
+import home.backend.domain.SetpointState;
+import home.backend.domain.SetpointsView;
+
+import java.io.IOException;
+import java.time.Duration;
+import java.time.Instant;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+/** F3: change setpoints directly or through a preset; the gateway enforces the limits (S1). */
+public class SetpointService {
+
+    /** Longest timed preset the user may choose; the gateway's own limit is higher. */
+    public static final int MAX_PRESET_HOURS = 4;
+
+    /** The chosen hours are not a whole number from 1 to {@link #MAX_PRESET_HOURS}, or the preset is not timed. */
+    public static class InvalidHoursException extends IllegalArgumentException {
+        InvalidHoursException(String message) {
+            super(message);
+        }
+    }
+
+    private final GatewayCommands gateway;
+    private final List<Preset> presets;
+
+    public SetpointService(GatewayCommands gateway, List<Preset> presets) {
+        this.gateway = gateway;
+        this.presets = List.copyOf(presets);
+    }
+
+    public SetpointsView current() throws IOException {
+        SetpointState state = gateway.setpoints();
+        return new SetpointsView(state.setpoints(), state.restores(), presets);
+    }
+
+    /** @param hours how long to keep the value, null until changed back */
+    public CommandResult apply(String setpoint, int value, Double hours, String user) throws IOException {
+        return gateway.apply(new Command(setpoint, value, duration(hours), user));
+    }
+
+    /** Puts the value from before the pending change back now, instead of waiting for its end. */
+    public RestoreResult restore(String setpoint, String user) throws IOException {
+        return gateway.restore(setpoint, user);
+    }
+
+    /**
+     * Empty if there is no such preset. A preset that does not fit the gateway's limits writes nothing.
+     * IOException only when no change was attempted; once writing starts, trouble is reported per change.
+     *
+     * @param until the end the user chose; required by a held preset, not allowed for any other
+     * @param hours how long a timed preset keeps its changes, 1 to {@link #MAX_PRESET_HOURS}; null keeps the preset's
+     * @param values the user's own value for some of the preset's setpoints (any preset); the rest keep the
+     *               preset's value
+     * @throws InvalidHoursException when {@code hours} is out of range or the preset has no hours to choose
+     * @throws IllegalArgumentException when {@code until} does not match what the preset needs, or a value is
+     *                                  for a setpoint the preset does not change or outside the gateway's limits
+     */
+    public Optional<PresetResult> applyPreset(String id, Instant until, Integer hours, Map<String, Integer> values,
+            String user)
+            throws IOException {
+        Optional<Preset> preset = presets.stream().filter(p -> p.id().equals(id)).findFirst();
+        if (preset.isEmpty()) {
+            return Optional.empty();
+        }
+        if (preset.get().isHeld() != (until != null)) {
+            throw new IllegalArgumentException(preset.get().isHeld() ? "preset " + id + " needs an end time"
+                    : "preset " + id + " has no end time to choose");
+        }
+        List<Change> changes = withHours(withValues(preset.get().changes(), values), hours);
+        List<Setpoint> limits = gateway.setpoints().setpoints();
+        requireWithinLimits(values, limits);
+        List<ChangeResult> checked = changes.stream().map(c -> check(c, preset.get().isHeld(), limits)).toList();
+        if (checked.stream().anyMatch(r -> r.status() == ChangeStatus.REJECTED)) {
+            return Optional.of(PresetResult.of(checked));
+        }
+        return Optional.of(PresetResult.of(run(changes, until, user)));
+    }
+
+    private static List<Change> withValues(List<Change> changes, Map<String, Integer> values) {
+        Set<String> own = changes.stream().map(Change::setpoint).collect(Collectors.toSet());
+        if (!own.containsAll(values.keySet())) {
+            throw new IllegalArgumentException("values may only be for the setpoints the preset changes: " + own);
+        }
+        return changes.stream().map(c -> new Change(c.setpoint(), values.getOrDefault(c.setpoint(), c.value()),
+                c.hours())).toList();
+    }
+
+    private static List<Change> withHours(List<Change> changes, Integer hours) {
+        if (hours == null) {
+            return changes;
+        }
+        if (hours < 1 || hours > MAX_PRESET_HOURS) {
+            throw new InvalidHoursException("hours must be 1 to " + MAX_PRESET_HOURS);
+        }
+        if (changes.stream().anyMatch(c -> c.hours() == null)) {
+            throw new InvalidHoursException("this preset has no hours to choose");
+        }
+        return changes.stream().map(c -> new Change(c.setpoint(), c.value(), hours.doubleValue())).toList();
+    }
+
+    private static void requireWithinLimits(Map<String, Integer> values, List<Setpoint> limits) {
+        for (Setpoint limit : limits) {
+            Integer value = values.get(limit.name());
+            if (value != null && !limit.allows(value)) {
+                throw new IllegalArgumentException(limit.name() + " must be " + limit.min() + "–" + limit.max()
+                        + " in steps of " + limit.step());
+            }
+        }
+    }
+
+    private List<ChangeResult> run(List<Change> changes, Instant until, String user) {
+        List<ChangeResult> results = new ArrayList<>();
+        for (Change change : changes) {
+            boolean stopped = !results.isEmpty() && results.getLast().status() != ChangeStatus.APPLIED;
+            results.add(stopped ? ChangeResult.notAttempted() : attempt(change, until, user));
+        }
+        return results;
+    }
+
+    private ChangeResult attempt(Change change, Instant until, String user) {
+        try {
+            var command = until == null ? new Command(change.setpoint(), change.value(), duration(change.hours()), user)
+                    : new Command(change.setpoint(), change.value(), null, until, user);
+            return ChangeResult.of(gateway.apply(command));
+        } catch (IOException e) {
+            return new ChangeResult(ChangeStatus.UNKNOWN, "no answer from the gateway", null);
+        }
+    }
+
+    /** REJECTED with the reason, or NOT_ATTEMPTED (nothing is sent if any change is rejected). */
+    private static ChangeResult check(Change change, boolean held, List<Setpoint> limits) {
+        String problem = problem(change, held, limits);
+        return problem == null ? ChangeResult.notAttempted() : new ChangeResult(ChangeStatus.REJECTED, problem, null);
+    }
+
+    private static String problem(Change change, boolean held, List<Setpoint> limits) {
+        Optional<Setpoint> known = limits.stream().filter(s -> s.name().equals(change.setpoint())).findFirst();
+        if (known.isEmpty()) {
+            return "preset sets " + change.setpoint() + ", which the gateway does not know";
+        }
+        if (!known.get().allows(change.value())) {
+            return "preset sets " + change.setpoint() + " to " + change.value() + ", outside the gateway's limits "
+                    + known.get().min() + "–" + known.get().max() + " step " + known.get().step();
+        }
+        // The gateway refuses a held raise too; asking first keeps a preset from stopping half way.
+        if (held && known.get().value() != null && change.value() >= known.get().value()) {
+            return "preset sets " + change.setpoint() + " to " + change.value() + ", which is not below the current "
+                    + known.get().value();
+        }
+        return null;
+    }
+
+    private static Duration duration(Double hours) {
+        if (hours == null) {
+            return null;
+        }
+        long minutes = Math.round(hours * 60);
+        if (minutes < 1 || minutes > Command.MAX_HOURS * 60L) {
+            throw new IllegalArgumentException("hours must be from one minute to " + Command.MAX_HOURS + " hours");
+        }
+        return Duration.ofMinutes(minutes);
+    }
+}

backend/src/main/java/home/backend/application/SnapshotFields.java

@@ -0,0 +1,71 @@
+package home.backend.application;
+
+import home.backend.domain.EnergyView.Source;
+import home.backend.domain.GatewaySnapshot;
+import home.backend.domain.GatewaySnapshot.DeviceSnapshot;
+import home.backend.domain.GatewaySnapshot.Measurement;
+
+import java.time.Duration;
+import java.time.Instant;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+
+/** Looks up one measurement of one device in a snapshot and reads typed fields. */
+final class SnapshotFields {
+
+    private SnapshotFields() {
+    }
+
+    /** Twice the 300 s the UI treats as one polling cycle; older than that a reading is not live. */
+    private static final Duration MAX_AGE = Duration.ofSeconds(600);
+
+    static Optional<DeviceSnapshot> device(GatewaySnapshot snapshot, String name) {
+        return snapshot.devices().stream().filter(d -> d.name().equals(name)).findFirst();
+    }
+
+    /** A reading is stale when the device link is down, it is missing, or it is older than twice a cycle. */
+    static boolean stale(Optional<DeviceSnapshot> device, Optional<Measurement> reading, Instant now) {
+        return stale(device, reading, now, MAX_AGE);
+    }
+
+    static boolean stale(Optional<DeviceSnapshot> device, Optional<Measurement> reading, Instant now,
+            Duration maxAge) {
+        return device.isEmpty() || !device.get().up() || reading.isEmpty()
+                || Duration.between(reading.get().time(), now).compareTo(maxAge) > 0;
+    }
+
+    /** One device's fields; empty when it is stale, so nothing old is shown as current. */
+    record Live(Source source, Map<String, Double> fields) {
+    }
+
+    static Live live(GatewaySnapshot snapshot, String device, String measurement, Instant now) {
+        return live(snapshot, device, measurement, now, MAX_AGE);
+    }
+
+    static Live live(GatewaySnapshot snapshot, String device, String measurement, Instant now, Duration maxAge) {
+        Optional<Measurement> reading = find(snapshot, device, measurement);
+        boolean stale = stale(device(snapshot, device), reading, now, maxAge);
+        Source source = new Source(device, reading.map(Measurement::time).orElse(null), stale);
+        return new Live(source, stale ? Map.of() : reading.get().fields());
+    }
+
+    static Optional<Measurement> find(GatewaySnapshot snapshot, String device, String measurement) {
+        return snapshot.devices().stream()
+                .filter(d -> d.name().equals(device))
+                .map(DeviceSnapshot::measurements)
+                .flatMap(List::stream)
+                .filter(m -> m.measurement().equals(measurement))
+                .findFirst();
+    }
+
+    static Integer whole(Map<String, Double> fields, String name) {
+        Double value = fields.get(name);
+        return value == null ? null : (int) Math.round(value);
+    }
+
+    static boolean on(Map<String, Double> fields, String name) {
+        Double value = fields.get(name);
+        return value != null && value != 0;
+    }
+}

backend/src/main/java/home/backend/application/StatsService.java

@@ -0,0 +1,89 @@
+package home.backend.application;
+
+import home.backend.domain.HeatPumpSample;
+import home.backend.domain.StatsView;
+import home.backend.domain.StatsView.Day;
+
+import java.io.IOException;
+import java.time.Clock;
+import java.time.Duration;
+import java.time.Instant;
+import java.time.LocalDate;
+import java.time.ZoneId;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.TreeMap;
+
+/**
+ * F2: the heat pump's work per local day over the last 7 or 30 days. A poll is taken to hold its
+ * outputs until the next poll, but at most {@link #MAX_HOLD}, so a gap in the data adds no hours.
+ */
+public class StatsService {
+
+    static final ZoneId ZONE = ZoneId.of("Europe/Warsaw");
+    static final Duration MAX_HOLD = Duration.ofSeconds(600);
+    private static final Map<String, Integer> RANGE_DAYS = Map.of("7d", 7, "30d", 30);
+
+    private final HeatPumpSamples repository;
+    private final Clock clock;
+
+    public StatsService(HeatPumpSamples repository, Clock clock) {
+        this.repository = repository;
+        this.clock = clock;
+    }
+
+    /**
+     * @param range {@code 7d} or {@code 30d}
+     * @throws IllegalArgumentException for an unknown range
+     */
+    public StatsView stats(String range) throws IOException {
+        Integer length = range == null ? null : RANGE_DAYS.get(range);
+        if (length == null) {
+            throw new IllegalArgumentException("unknown range: " + range);
+        }
+        Instant now = clock.instant();
+        LocalDate first = now.atZone(ZONE).toLocalDate().minusDays(length - 1);
+        Map<LocalDate, DayTally> tallies = new TreeMap<>();
+        for (int i = 0; i < length; i++) {
+            tallies.put(first.plusDays(i), new DayTally());
+        }
+        tally(repository.samples(first.atStartOfDay(ZONE).toInstant(), now), now, tallies);
+
+        DayTally all = new DayTally();
+        List<Day> days = new ArrayList<>();
+        tallies.forEach((date, tally) -> {
+            days.add(tally.day(date));
+            all.add(tally);
+        });
+        return new StatsView(range, days, all.totals());
+    }
+
+    private static void tally(List<HeatPumpSample> samples, Instant now, Map<LocalDate, DayTally> tallies) {
+        HeatPumpSample previous = null;
+        for (int i = 0; i < samples.size(); i++) {
+            HeatPumpSample s = samples.get(i);
+            DayTally day = tallies.get(s.t().atZone(ZONE).toLocalDate());
+            day.sample(s);
+            if (previous != null && previous.compressor() != null && previous.compressor() == 0
+                    && DayTally.on(s.compressor())) {
+                day.start();
+            }
+            previous = s;
+            hold(s, i + 1 < samples.size() ? samples.get(i + 1).t() : now, tallies);
+        }
+    }
+
+    /** Adds the time {@code s} was in force to the days it falls in; a stretch over midnight is split. */
+    private static void hold(HeatPumpSample s, Instant next, Map<LocalDate, DayTally> tallies) {
+        Instant end = Duration.between(s.t(), next).compareTo(MAX_HOLD) > 0 ? s.t().plus(MAX_HOLD) : next;
+        Instant at = s.t();
+        while (at.isBefore(end)) {
+            LocalDate date = at.atZone(ZONE).toLocalDate();
+            Instant midnight = date.plusDays(1).atStartOfDay(ZONE).toInstant();
+            Instant stop = midnight.isBefore(end) ? midnight : end;
+            tallies.get(date).hold(s, Duration.between(at, stop));
+            at = stop;
+        }
+    }
+}

backend/src/main/java/home/backend/application/WarningSource.java

@@ -0,0 +1,12 @@
+package home.backend.application;
+
+import home.backend.domain.WeatherView.Warning;
+
+import java.io.IOException;
+import java.util.List;
+
+/** Weather warnings that cover the house, whether in force now or announced. */
+public interface WarningSource {
+
+    List<Warning> warnings() throws IOException;
+}

backend/src/main/java/home/backend/application/WeatherService.java

@@ -0,0 +1,98 @@
+package home.backend.application;
+
+import home.backend.application.Cached.Entry;
+import home.backend.domain.Forecast;
+import home.backend.domain.Forecast.DailyForecast;
+import home.backend.domain.PvCalibration;
+import home.backend.domain.WeatherCodes;
+import home.backend.domain.WeatherView;
+import home.backend.domain.WeatherView.Day;
+import home.backend.domain.WeatherView.Now;
+import home.backend.domain.WeatherView.Warning;
+
+import java.io.IOException;
+import java.time.Clock;
+import java.time.Duration;
+import java.time.LocalDate;
+import java.time.ZoneId;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+/** Forecast, PV estimate and warnings, each kept for a while so the phones do not load the sources. */
+public class WeatherService {
+
+    private static final ZoneId ZONE = ZoneId.of("Europe/Warsaw");
+    private static final int CALIBRATION_DAYS = 14;
+
+    private record Calibrated(Forecast forecast, Double factor) {
+    }
+
+    private final Clock clock;
+    private final PvEnergyRepository pv;
+    private final Cached<Calibrated> forecast;
+    private final Cached<List<Warning>> warnings;
+
+    public WeatherService(ForecastSource forecastSource, WarningSource warningSource, PvEnergyRepository pv,
+            Clock clock) {
+        this.clock = clock;
+        this.pv = pv;
+        this.forecast = new Cached<>(Duration.ofMinutes(30), ZONE, clock, () -> calibrated(forecastSource.forecast()));
+        this.warnings = new Cached<>(Duration.ofMinutes(10), clock, warningSource::warnings);
+    }
+
+    /** @throws IOException when there is no forecast at all; warnings alone may be missing. */
+    public WeatherView current() throws IOException {
+        Entry<Calibrated> weather = forecast.get();
+        Entry<List<Warning>> warned = warnings();
+        LocalDate today = LocalDate.now(clock.withZone(ZONE));
+        Calibrated w = weather.value();
+        return new WeatherView(clock.instant(),
+                day(w, today), day(w, today.plusDays(1)), day(w, today.plusDays(2)),
+                new Now(w.forecast().temperature()), inForce(warned.value()), w.factor(),
+                weather.stale() || warned.stale());
+    }
+
+    private Entry<List<Warning>> warnings() {
+        try {
+            return warnings.get();
+        } catch (IOException e) {
+            return new Entry<>(List.of(), true);
+        }
+    }
+
+    private List<Warning> inForce(List<Warning> all) {
+        return all.stream().filter(w -> w.to().toInstant().isAfter(clock.instant())).toList();
+    }
+
+    private Calibrated calibrated(Forecast fetched) {
+        LocalDate today = LocalDate.now(clock.withZone(ZONE));
+        Map<LocalDate, Double> radiation = new HashMap<>();
+        fetched.days().forEach((date, day) -> {
+            if (day.radiationMj() != null) {
+                radiation.put(date, day.radiationMj());
+            }
+        });
+        try {
+            var measured = pv.dailyKwh(today.minusDays(CALIBRATION_DAYS), today);
+            return new Calibrated(fetched, PvCalibration.factor(measured, radiation));
+        } catch (IOException e) {
+            return new Calibrated(fetched, null);
+        }
+    }
+
+    private static Day day(Calibrated w, LocalDate date) throws IOException {
+        DailyForecast d = w.forecast().days().get(date);
+        if (d == null) {
+            throw new IOException("forecast has no " + date);
+        }
+        Double kwh = w.factor() == null || d.radiationMj() == null ? null : round(w.factor() * d.radiationMj());
+        Double sunshine = d.sunshineSeconds() == null ? null : round(d.sunshineSeconds() / 3600);
+        return new Day(date, d.weatherCode(), WeatherCodes.describe(d.weatherCode()), d.tMax(), d.tMin(),
+                d.precipitationMm(), sunshine, kwh);
+    }
+
+    private static double round(double value) {
+        return Math.round(value * 10) / 10.0;
+    }
+}

backend/src/main/java/home/backend/domain/AuditEntry.java

@@ -0,0 +1,14 @@
+package home.backend.domain;
+
+import java.time.Instant;
+
+/**
+ * One audited write. {@code unit} is "°C", "%", "HHMM" (a clock time written as 1830) or "0/1" (off/on);
+ * the values are null when the gateway did not record them.
+ */
+public record AuditEntry(Instant time, String source, String what, Integer oldValue, Integer newValue,
+        String unit, String who, String status) {
+
+    public static final String HEAT_PUMP = "heat_pump";
+    public static final String BATTERY = "battery";
+}

backend/src/main/java/home/backend/domain/AuditView.java

@@ -0,0 +1,7 @@
+package home.backend.domain;
+
+import java.util.List;
+
+/** The audited writes of the heat pump and the battery, newest first. */
+public record AuditView(List<AuditEntry> entries) {
+}

backend/src/main/java/home/backend/domain/BatteryChange.java

@@ -0,0 +1,19 @@
+package home.backend.domain;
+
+import java.time.LocalTime;
+import java.util.List;
+
+/**
+ * A change of the Time of Use switch and of single program slots (1 to 6); a null field stays as it is.
+ * The gateway checks every rule (ADR-013).
+ */
+public record BatteryChange(Boolean enabled, List<Slot> slots) {
+
+    public BatteryChange {
+        slots = slots == null ? List.of() : List.copyOf(slots);
+    }
+
+    /** {@code from} is the slot's start, to the minute. */
+    public record Slot(int slot, LocalTime from, Integer socPct, Boolean gridCharge) {
+    }
+}

backend/src/main/java/home/backend/domain/BatteryResult.java

@@ -0,0 +1,13 @@
+package home.backend.domain;
+
+import java.util.Map;
+
+/**
+ * The gateway's verdict on a battery change, passed on unchanged. REJECTED: refused by the rules, nothing
+ * written. STALE: the inverter's settings are unknown or changed meanwhile, nothing written. TOO_SOON: S4.
+ * FAILED: a write or its read-back went wrong; {@code read} has the registers as read back.
+ */
+public record BatteryResult(Status status, String message, Map<Integer, Integer> read) {
+
+    public enum Status { APPLIED, REJECTED, STALE, TOO_SOON, FAILED }
+}

backend/src/main/java/home/backend/domain/BatteryView.java

@@ -0,0 +1,39 @@
+package home.backend.domain;
+
+import java.time.Instant;
+import java.util.List;
+
+/**
+ * The Deye's battery (F7), read-only. Power in W, + discharge / − charge. The live values
+ * ({@code time}, {@code stale}) come from the Deye's readings and are null when stale; the settings
+ * ({@code settingsTime}, {@code settingsStale}: mode, schedule, limits, capacity) come from their own,
+ * slower reading and are null (empty schedule) when stale. The capacity assumes the nominal 51.2 V.
+ * {@code reserve} is the app's backup reserve (ADR-013) and {@code editable} says the gateway accepts
+ * changes; they are null and false when it does not.
+ */
+public record BatteryView(Instant time, boolean stale, Double socPct, Double powerW, Double voltageV,
+        Double currentA, Double temperatureC, Double capacityKwh, Energy today, Energy total, Mode mode,
+        List<Slot> schedule, Limits limits, Instant settingsTime, boolean settingsStale, Reserve reserve,
+        boolean editable) {
+
+    /** The share of the battery kept for a power cut, and the lowest the user may set. */
+    public record Reserve(int pct, int floorPct) {
+    }
+
+    /** Battery energy in kWh. */
+    public record Energy(Double chargeKwh, Double dischargeKwh) {
+    }
+
+    /** Time of use on means the battery follows the schedule; off means backup only. */
+    public record Mode(boolean touEnabled, String description) {
+    }
+
+    /** A program slot, {@code from} and {@code to} as HH:MM; it runs until the next slot starts. */
+    public record Slot(String from, String to, int powerW, int socPct, boolean gridCharge) {
+    }
+
+    public record Limits(Integer maxChargeA, Integer maxDischargeA, Integer shutdownSocPct,
+            Integer lowSocPct, Integer restartSocPct, boolean gridChargeEnabled, Integer gridChargeCurrentA,
+            Integer gridChargeStartSocPct) {
+    }
+}

backend/src/main/java/home/backend/domain/Command.java

@@ -0,0 +1,19 @@
+package home.backend.domain;
+
+import java.time.Duration;
+import java.time.Instant;
+
+/**
+ * Set a setpoint. With a duration the gateway restores the old value afterwards; with
+ * {@code heldUntil} it holds a lowering value until then without renewals (ADR-012); else it stays
+ * while the backend renews the lease (ADR-011).
+ */
+public record Command(String setpoint, int value, Duration duration, Instant heldUntil, String requestedBy) {
+
+    public Command(String setpoint, int value, Duration duration, String requestedBy) {
+        this(setpoint, value, duration, null, requestedBy);
+    }
+
+    /** The gateway refuses longer boosts too; we refuse first, so the phone gets a clear 400. */
+    public static final int MAX_HOURS = 72;
+}

backend/src/main/java/home/backend/domain/CommandResult.java

@@ -0,0 +1,10 @@
+package home.backend.domain;
+
+import java.time.Instant;
+
+/** The gateway's verdict on a command, passed on to the phone unchanged. */
+public record CommandResult(Status status, String message, Instant restoreAt) {
+
+    /** REJECTED: refused before any write. FAILED: the write or its read-back failed. */
+    public enum Status { APPLIED, REJECTED, FAILED }
+}