Report client exceptions PostHog can process; never report an already-running daemon as a crash

[Chrrxs]

Summary

Two client error-reporting defects found while reviewing PostHog errors (2026-10-03..07):

1. Exceptions with a nameless stack frame never reached Error Tracking. parseStackFrames left function undefined for frames like at file:line:col; PostHog's error-tracking processor rejects such an event ($cymbal_errors: "missing field \function`") and it gets no issue. 31 client exceptions in 30 days were invisible this way, including today's HTTP 409: dead-lettering batchobservation-upload errors. Such frames are now named?`, as PostHog's own stack parser names them.
2. Starting a daemon that already runs was reported as a fatal crash, twice. The detached child threw a plain Error on already_running, and both it and its parent reported a fatal daemon_startup crash (42 events in 15 minutes when several MCP shims started a daemon at once). It is now DaemonAlreadyRunningError: the child tells its parent over the startup handshake (already-running), says so plainly and exits non-zero without a report; the background launcher prints the running PID and exits 0. Any other startup failure is still reported as a fatal crash.

Verification

• New tests fail on main and pass here: apps/observer/tests/error-reporting/sanitize.test.ts, apps/observer/tests/recovery-healing.test.ts ("starting a daemon that already runs").
• pnpm lint, pnpm typecheck, check:boundaries, check:secrets pass locally (Node 22).
• pnpm test: all pass except tests that need a local Deno (read-only-broker, local-executor-native-workflow) and user-service-manager "enables an active matching service that was left disabled at login", which fails the same way on clean main in this environment.

Migrations & Breaking Changes

• Protocol: the daemon's private parent/child startup handshake gains an already-running message; both ends ship in the same entry file.
• No schema, cloud contract or public API change. Rollback is a plain revert.

Privacy

Frames carry the same sanitized fields as before; only the placeholder name ? is added. Nothing new is reported; one fatal report is removed.