control board: stale registrations and a launch-test leak (#1504)

Two defects in 69f99323, reported by the professor session and verified.

The darkwing launch test's flock-contention spawn ran without the fixture
config, so launch.sh re-entered scripts/mosaic against the real data root
and wrote fixture records for darkwing, dewey and filbert there. That
spawn now names the fixture config, and both launch test files set
MOSAIC_CONFIG to a nonexistent path and clear MOSAIC_LAUNCH_REGISTERED
process-wide, so a spawn that forgets fails instead of polluting.

A registration is written before the launch script's own checks, so a
refused launch left a record with a dead pid that the board honoured. The
scanner now probes the recorded pid (pidAlive, signal 0); a gone pid makes
the record stale: still on the Registered line with alive false, derived
task, project and workspace win, index gains registrationStale, CLI
summary gains a stale count.

Fleet launchers marked not planned per Jason. Board 90/90, seat 15/15,
launch scripts 5/5. Sonnet review APPROVED.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

BUILD-LOG.md

@@ -2102,3 +2102,23 @@ on the way: Jason's own launch refused on the Pi pin because
 `node_modules` still held 0.84.4 after commit 557aba0f moved the pin to
 0.85.1; `npm ci` fixed it and the refusal message now names both versions.
 The pin is canon and stays unless Jason decides otherwise.
+
+## 2026-09-12 — Seat registration follow-up: test leak and stale records (#1504)
+
+Before: the darkwing launch test's flock-contention spawn ran without the
+fixture config, so `launch.sh` re-entered `scripts/mosaic` against the real
+data root and wrote fixture records for darkwing, dewey and filbert there
+(dead pids, `/tmp` workspaces), overwriting Jason's live darkwing record.
+Separately, a launch the script itself refused (Pi pin) left a record with
+a dead pid that the board showed as registered. Both reported by the
+professor session, verified against the commit and the data root.
+
+After: the spawn names the fixture config; both launch test files set
+`MOSAIC_CONFIG` to a nonexistent path and clear `MOSAIC_LAUNCH_REGISTERED`
+process-wide so a forgotten env fails instead of polluting. The scanner
+probes the recorded pid (`pidAlive`, signal 0, EPERM counts as alive); a
+gone pid marks the record stale: kept on the Registered line with
+`registered.alive` false, derived values win, `registrationStale` on the
+index, stale count in the CLI summary. Fleet launchers marked not planned
+per Jason. Tests: board 90/90, seat 15/15, launch scripts 5/5, real data
+root untouched by the run. The three fixture records were deleted by hand.