test: the mock can inject an alternating-sign impulse train on sine

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

docs/claude/build-and-run.md

@@ -60,6 +60,25 @@ the value is required, and the popover button uses 1000 when the flag was absent
 The flag is **not** persisted in the session file: persistence of the enable state
 belongs with `todo.md` item 3, alongside the relative-time toggle.
 
+`tools/mock_udpstreamer.py` has waveform-injection options used by the probes:
+
+- `--glitch-at S` / `--glitch-width W` invert the `square` signal for `W` seconds at the
+  start of every square period from stream second `S` onwards — a runt pulse of a known
+  width, which is what a `<` pulse-width trigger and a glitch search are checked against.
+- `--quiet-at S` freezes `sine` at its held value from stream second `S` onwards, so it
+  stops crossing zero: the dropout trigger's input.
+- `--spike-every S` / `--spike-amp A` / `--spike-width N` inject an alternating-sign
+  impulse train onto `sine` only — the other four signals (`time`, `square`, `ramp`,
+  `noise`) are untouched, which is what lets a probe compare a spiked channel against a
+  clean one in the same run. Every `S` seconds a spike of `N` samples at amplitude `A` is
+  added to `sine`; the sign alternates per period because a one-signed train is a DC offset
+  a median would partly track rather than reject. `N` is in **samples**, not seconds, so its
+  duration follows `--rate`. `0` (the default for both `S` and `A`) injects nothing, so
+  every existing invocation is unchanged. **`--batch` must stay at or below 1000** with or
+  without these options: 2000 samples × 5 signals × `f64` is 80 kB and exceeds UDP's
+  ~65507-byte payload limit, and the mock dies on its first `sendto` with
+  `OSError: [Errno 90] Message too long` while the run still exits 0.
+
 Run with no `--server` and udpscope asks which source to open: the sessions it has stored, plus a
 form for a new host. Every probe below passes `--server`, so none of them sees it.