flatudp: the source, kind, mock sender and stream probes

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/claude/verification.md

@@ -423,7 +423,7 @@ precedent, not an exception.
 - `UDPSCOPE_PROBE_SOURCE_KINDS=2000` with `UDPSCOPE_EXIT_AFTER_MS=5000`, run as `--source probe --source-opt rate=500`
   -- the source-plugin path end to end. The variable's presence also registers the test-only `probe` kind (a
   synthetic sine with one panel), so it is the only way a run sees that kind; its value is the delay in ms.
-  Eight `[source-kinds]` lines (one `form` line per registered kind: `udps`, `e1608`, `probe`); the
+  Nine `[source-kinds]` lines (one `form` line per registered kind: `udps`, `e1608`, `flatudp`, `probe`); the
   reading's own entry is in `probe-readings.md`.
 - `UDPSCOPE_PROBE_E1608=1500` with `UDPSCOPE_EXIT_AFTER_MS`, run as `--source e1608` against
   `tools/mock_e1608.py` -- the MCC E-1608 end to end: panels present and sensitive, a DAC write, a
@@ -441,6 +441,24 @@ precedent, not an exception.
   - **a rejected code:** mock `--code 1234`, app `code=7`: one error line, the retries stop.
 - `UDPSCOPE_PROBE_E1608_RECONNECT=8000` -- reads the source after the mock dropped the link and 500 ms
   later checks the frame count moved on. The reading's own entry is in `probe-readings.md`.
+- `UDPSCOPE_PROBE_FLATUDP=2500` with `UDPSCOPE_EXIT_AFTER_MS`, run as `--source flatudp` against
+  `tools/mock_flatudp.py` -- the flat UDP source end to end: a hand-computed codec and decode check (it
+  needs no source), the stream's signal names and declared rate, the channel count (one per signal), value
+  continuity across the first two signals (all-scalar lists only), the wrong-size accounting and the capture
+  button. It enables the signals itself, so do **not** add `UDPSCOPE_ENABLE_ALL_MS`. Runs, each short and
+  serial, with the mock killed afterwards (quote the `signals` value: zsh globs the `[4]`):
+  - **mixed list, gap and bad datagrams:** mock `--rate 1000 --signals Trigger:uint8,Ia:float32,Cnt:uint64,Wave:int16[4]
+    --gap 9,5 --bad-every 1 --log /tmp/flatudp-mock.log` started 1 s before the app, the same `signals` as a
+    `--source-opt`, with `UDPSCOPE_PROBE_FLATUDP=2500 UDPSCOPE_PROBE_FLATUDP_GAP=8000 UDPSCOPE_EXIT_AFTER_MS=14500`;
+    stderr carries exactly one `datagram of 22 bytes, expected 21` line. The mock's clock starts about 4 s
+    before the app's probe clock (`xvfb-run` and the app's own startup), so a gap of 9 s to 14 s on the mock's
+    clock covers the app's 8 s probe (silence) and ends before its 12 s one (resumed); a mock gap measured in
+    the app's own seconds would miss both;
+  - **scalar list, big endian (batching, continuity):** mock `--signals Trigger:uint8,Ia:float32,Cnt:uint64 --big-endian`,
+    app `--source-opt endian=big`, `UDPSCOPE_PROBE_FLATUDP=2500 UDPSCOPE_EXIT_AFTER_MS=5000`;
+  - **no sender:** `connected=0` throughout, a reading and not a failure.
+- `UDPSCOPE_PROBE_FLATUDP_GAP=8000` -- reads the source inside the mock's silence (2 s after its last datagram
+  the source is disconnected) and 4 s later checks it reconnected and the stream moved on.
 - `UDPSCOPE_PROBE_SEARCH_MS` — runs a buffer search for the armed condition, cross-checks the live
   trigger's own `t0` against the nearest hit (`agree=1` is the load-bearing reading), and jumps to
   hit 0. Reports the resulting `mode=`, `axis=` and `marks placed=`.