docs: the source-plugin framework, the --source options and the source-kinds probe

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

docs/claude/verification.md

@@ -13,7 +13,9 @@ xvfb-run -a env UDPSCOPE_EXIT_AFTER_MS=8000 UDPSCOPE_ENABLE_ALL_MS=1000 \
   ./build/udpscope --server 127.0.0.1 --port 8000
 ```
 
-Two baselines every run is read against. A clean build emits **three** warnings and no more: two
+Two baselines every run is read against. The UDPS runs must be **unchanged by the source-plugin work**:
+a UDPS self-check, number-normalised (`sed 's/[0-9.]\+/N/g'`), diffs empty against one taken before it.
+A clean build emits **three** warnings and no more: two
 `-Wmissing-field-initializers` on `MathNode::source` and one `-Woverlength-strings` on the icons'
 generated GResource `.c`, whose blob is **12352** against C99's 4095-byte string-literal limit with
 the seven action icons and the two app icons that remain (a note about a generated file, which GCC
@@ -418,6 +420,10 @@ precedent, not an exception.
   defect where the accumulation is gated on the visible tab, which would leave a gap in min/max/avg for
   exactly as long as the trigger was on screen. It enables *and plots* its own signal, so it needs no other
   probe ahead of it. The reading's own entry is in `probe-readings.md`.
+- `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.
+  Seven `[source-kinds]` lines; the reading's own entry is in `probe-readings.md`.
 - `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=`.