docs(energy): note the meter converter's stray ACKs and Deye resets

Both show up in the Pi's journal and look like faults: packets from a
public address on port 502, and Deye going down every 3 hours. Neither
loses readings, so record them where the next reader looks.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015x6FWeKCY59JfFJmzAm4TL

gateway/src/test/java/home/gateway/GatewayEndToEndTest.java

@@ -133,7 +133,7 @@ class GatewayEndToEndTest {
         waitFor(() -> controllerWrites().size() == 2);
 
         assertEquals(List.of(1, 4143, 38), controllerWrites().get(1));
-        assertEquals(1, controller.peakOpenConnections(), "the MK01 drops a client when a second one connects");
+        assertEquals(1, controller.connections(), "the MK01 drops a client when a second one connects");
 
         gateway.close(); // flushes the audit lines, which otherwise wait for the next flush period
         var audit = auditLines().toList();

gateway/src/test/java/home/gateway/adapters/modbus/MockModbusServer.java

@@ -30,7 +30,6 @@ public final class MockModbusServer implements Closeable {
     private final Map<Integer, Integer> input = new ConcurrentHashMap<>();
     private final AtomicInteger connections = new AtomicInteger();
     private final AtomicInteger open = new AtomicInteger();
-    private final AtomicInteger peakOpen = new AtomicInteger();
     private final List<int[]> writes = new CopyOnWriteArrayList<>();
     private final List<int[]> multipleWrites = new CopyOnWriteArrayList<>();
     private volatile Duration responseDelay = Duration.ZERO;
@@ -69,11 +68,6 @@ public final class MockModbusServer implements Closeable {
         return open.get();
     }
 
-    /** The most connections that were open at the same time. */
-    public int peakOpenConnections() {
-        return peakOpen.get();
-    }
-
     public void holding(int address, int value) {
         holding.put(address, value);
     }
@@ -141,7 +135,7 @@ public final class MockModbusServer implements Closeable {
             try {
                 Socket client = server.accept();
                 connections.incrementAndGet();
-                peakOpen.accumulateAndGet(open.incrementAndGet(), Math::max);
+                open.incrementAndGet();
                 Thread.ofVirtual().start(() -> serve(client));
             } catch (IOException e) {
                 return;

research/energy/README.md

@@ -93,6 +93,14 @@ House meter SDM630 (`electricity.PRAD2`): `total_power_active` is **+ import /
 Deye grid registers. Checked 2026-10-23 in InfluxDB: −2.5 to −5.5 kW between 11:00 and 15:00 local
 while PV exported, +645 W at night matching Deye's 640 W import.
 
+Link quirks seen from the gateway on the Pi (2026-10-24/25), both harmless to the readings:
+
+- The meter's RS485 converter (`192.168.0.10`, MAC `d8:b0:4c:bc:7a:8e`) sends late TCP ACKs from
+  port 502 with the source address `76.85.0.32` (TTL 255, so from the LAN, not the internet).
+  ufw drops them, about 1800 `[UFW BLOCK]` journal lines a day; the polls themselves succeed.
+- The Solarman logger resets our connection about every 3 h, always near :12
+  (`deye is down: Connection reset`); the next poll a minute later works again.
+
 Considered and rejected (2026-10-23): pointing the logger's second server ("Server B") at our
 backend. Push frames are poorly documented binary data every ~5 min, need a TCP server with
 acks, and a wrong setting could cut off the Solarman cloud my father uses. Local FC3 polling