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

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

docs/claude/build-and-run.md

@@ -135,6 +135,25 @@ python3 tools/mock_e1608.py --port 54711 &
   --source-opt ai0=BIP10V --source-opt ai1=BIP5V --source-opt plot0=1
 ```
 
+`--source flatudp` receives the MARTe2 `UDPSender` datasource (one datagram per cycle: the signals
+concatenated in declaration order, no header, no padding). The datagram carries **no description**, so the
+settings are the whole contract: `port` 44488, `bind`, `multicast` and `iface` (a group to join and the local
+interface for it), `rate` (the sender's cycle rate in Hz; **required**, it sizes the ring and the ingest
+decimation and spaces the samples within a frame), `endian` `little|big`, and `signals`
+`name:type[count],...` with types `uint8/16/32/64`, `int8/16/32/64`, `float32`, `float64` (a count above 1
+makes a vector signal: one channel whose `count` values per datagram are consecutive samples, as a UDPStreamer
+block signal), e.g. `Trigger:uint8,Ia:float32,Wave:float32[16]`. A datagram of any other size than
+the list implies is dropped and counted as stale; each distinct wrong size is reported once on stderr as
+`[flatudp] ...`. Loss is never reported: the stream has no counter. `tools/mock_flatudp.py` is a sender for
+a signal spec (`--rate`, `--signals`, `--big-endian`, `--gap S,D`, `--bad-every S`, `--multicast G --mcast-if A`,
+`--log FILE`).
+
+```sh
+python3 tools/mock_flatudp.py --port 44588 --rate 1000 --signals Trigger:uint8,Ia:float32,Wave:int16[4] &
+./build/udpscope --source flatudp --source-opt port=44588 --source-opt rate=1000 \
+  --source-opt signals=Trigger:uint8,Ia:float32,Wave:int16[4]
+```
+
 `tools/mock_udpstreamer.py` has waveform-injection options used by the probes:
 
 - `--square-harmonics N` shapes `square`: `N` odd harmonics of the ideal step's Fourier