feat: stateless daemon core (ADR 004)

[c-h-]

Summary

Implements ADR 004: Stateless Daemon Core — the daemon stops being a session database and becomes a stateless multiplexer.

Root cause: The daemon maintained a state.json session registry that mirrored every session discovered by every adapter. Over 26 hours, this accumulated 394 "active" sessions because OpenClaw sessions (no PID) had no exit path. Pruning was a band-aid on a fundamental design flaw.

Fix: Adapters own session truth. Daemon owns what it launched.

Changes

Phase 1: Fix session accumulation bug

• reconcileAndEnrich() detects sessions that disappear from adapter discover() results and marks them stopped + autoUnlock
• 30-second grace period for recently-launched sessions to avoid false positives from adapter discovery latency

Phase 2: Make session.list adapter-first

• session.list handler fans out discover() to all adapters in parallel with 5s per-adapter timeouts
• Merges results and enriches with daemon launch metadata (prompt, group, spec, cwd)
• session.status also fans out to adapters for fresh data
• Graceful degradation: failed adapters are skipped, partial results returned

Phase 3: Clean up

• Removed: SessionTracker.poll(), reapStaleEntries(), validateAllSessions(), pruneDeadSessions(), pruneOldSessions(), listSessions(), activeCount(), startPolling(), stopPolling()
• Removed: 5-second polling interval and all background state reconciliation
• Added: lightweight 30s PID liveness check for lock cleanup (startLaunchCleanup)
• Decoupled MetricsRegistry from SessionTracker; active session count updated on session.list calls
• session.prune kept for backward compat, now runs PID liveness cleanup

Architecture

Before: CLI → daemon → StateManager (stale cache of all sessions)
                         ↑ SessionTracker.poll() every 5s

After:  CLI → daemon → fan-out adapter.discover() → merge → return
                ↓
        StateManager (minimal: launch metadata, locks, fuses only)

Testing

• All 388 tests pass (386 original + 2 new for active session metrics)
• Rewrote session-tracker.test.ts for new stateless behavior (22 tests)
• npm test, npm run typecheck, npx biome check all clean

Fixes #51

[c-h-]

Reviewed — clean implementation of ADR 004. Fan-out + reconcile is much simpler than the polling/pruning tower. Grace period for recently-launched sessions is a nice touch. Tests comprehensive. ⚡