fix(hook): route annotate-last to the live Copilot CLI session

[mararn1618]

Problem

Fixes Issue #1149,

Under Copilot CLI, plannotator last / annotate-last has no Copilot branch: the handler tries --stdin, Codex and droid, then falls through to the default transcript reader and silently annotates a message from an unrelated old session. The env check meant to catch Copilot (process.env.COPILOT_CLI) can never fire because Copilot CLI does not set that variable, and on a full install the shared plannotator-last skill shadows the Copilot plugin command, so this broken path is what /plannotator-last actually runs.

Approach

Copilot CLI leaves no env fingerprint, but every live session holds $COPILOT_HOME/session-state/<uuid>/inuse.<pid>.lock with the pid of its copilot process. The hook walks its ancestor pids (the existing getAncestorPids in session-log.ts) and matches them against those locks, which resolves the exact session that spawned the hook instead of guessing by cwd and mtime. Two guards:

• locks can outlive their session and pids get reused, so a match only counts while the lock pid still names a copilot process (ps -o comm=)
• where the process walk or ps is unavailable (Windows), detection resolves nothing and behavior stays exactly as today

annotate-last takes the Copilot branch when a lock matches, or when PLANNOTATOR_ORIGIN=copilot-cli is set (then with the existing cwd heuristic as fallback), reads messages through the existing reader in copilot-session.ts (getRecentCopilotMessages), and reports origin copilot-cli to the annotate server. The stdin, Codex and droid branches keep priority and are untouched. copilot-last prefers the lock match over its cwd heuristic. The global origin chain in index.ts is deliberately not modified.

Commits

• fix(hook): add Copilot session lock detection. Matcher plus ancestor resolver in copilot-session.ts, unit tests, and the stale COPILOT_CLI=1 header claim corrected.
• fix(hook): route annotate-last to the live Copilot session. The new branch and origin reporting.
• fix(hook): prefer ancestor lock match in copilot-last. Separate commit, easy to drop if you would rather keep the pure cwd heuristic there.
• docs(cli): document copilot-last in help. The subcommand worked but was missing from --help.

Testing

• 13 new unit tests (copilot-session.test.ts): lock match, no match, several live sessions, pid order in the chain, malformed lock names, stale lock skipped, pid-reuse guard, failing process name lookup, COPILOT_HOME override.

• Full bun test: no change against an untouched main checkout on my machine apart from the 13 new passing tests; the few suites that fail here fail identically before and after (environment related).

• End to end inside a real Copilot session (macOS 26.5.2, Copilot CLI 1.0.75) with PLANNOTATOR_DEBUG=1:

  [DEBUG] Copilot detected, project root: /private/tmp/.../copilot-e2e
  [DEBUG] Copilot ancestor lock session: /Users/work1618/.copilot/session-state/0782e7a1-e654-485f-b822-4e1618703d1b
  [DEBUG] Copilot selected session: /Users/work1618/.copilot/session-state/0782e7a1-e654-485f-b822-4e1618703d1b
  

  The resolved uuid is the invoking session: the same run's summary footer printed copilot --resume=0782e7a1-e654-485f-b822-4e1618703d1b.

• Negative control from a terminal outside Copilot: no Copilot lines in the debug output, the default transcript resolution runs unchanged.

• PLANNOTATOR_ORIGIN=copilot-cli outside Copilot: the Copilot branch is taken with no lock match and the session resolves via the cwd heuristic.

Possible follow-up

The same lock detection could back the global origin chain in index.ts so every mode gains Copilot awareness. Left out to keep this change scoped to the -last flows.