ca-arbiter

# $ca-arbiter — restore orchestration The exit door for `$ca-dev`. No-op if dev mode is not active. ## Flow 1. **Log exit** — append to `<project-root>/.codearbiter/overrides.log` (append-only, `>>`): ``` [ISO-8601 timestamp] | BY: <email> | DEV: exit ``` 2. **Marker** — remove `<project-root>/.codearbiter/.markers/dev-active`. 3. **Resume** — re-present the startup state (stage, blocking `CONFIRM-NN`, in-flight tasks) and await a slash command. Orchestration, routing, and all gates are back in force. ## Hard gate MUST write the `DEV: exit` line to `overrides.log` and remove the `dev-active` marker before resuming orchestration — the exit is on the audit trail like the entry. MUST NOT rewrite or truncate `overrides.log` — the append-only rule has no dev exception, on entry or exit. If a prior session ended mid-dev, SessionStart has already appended the synthetic `BY: session-cleanup | DEV: exit` close line and cleared the marker (`session-start.py`, observability-001). In that case MUST NOT write a second `DEV: exit` for that orphaned entry — the close is already on the trail. Session-scoped clearing (#271): SessionStart's synthetic close is now conditional on the marker plausibly being abandoned rather than owned by a different, still-live session — it will NOT clobber another concurrently-running session's live `/dev` marker or write a false `DEV: exit` for it. `$ca-arbiter` remains the ONLY way to cleanly close your OWN `/dev` session's audit pair; do n...