probe: name the MathNode fields; the build baseline is now one warning

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

CLAUDE.md

@@ -39,7 +39,7 @@ The detail lives in `docs/claude/`. Read the files that touch the area you are e
 | File | What it covers |
 | --- | --- |
 | [build-and-run.md](docs/claude/build-and-run.md) | Configuring and building, the desktop-entry target, the command-line options, and the two vendored dependencies (`deps/plotter`, `deps/udpsclient`) including what was changed upstream and why. |
-| [verification.md](docs/claude/verification.md) | How to run the headless self-check, the **two baselines every run is read against** (exactly three build warnings; no `Gtk-CRITICAL`), and the environment variable that schedules each probe. |
+| [verification.md](docs/claude/verification.md) | How to run the headless self-check, the **two baselines every run is read against** (exactly one build warning; no `Gtk-CRITICAL`), and the environment variable that schedules each probe. |
 | [probe-readings.md](docs/claude/probe-readings.md) | The per-line reference for the self-check's output: what every probe and dump line means, the value it must read, and the defect a wrong reading names. |
 
 ### How the application is put together