feat(agents): add DroidAgentWatcher for Factory Droid sessions

[panosAthDBX]

Summary

Adds a new agent watcher for Factory Droid sessions, following the existing pattern used by Claude Code, Codex, Amp, OpenCode, and Pi.

• Watches ~/.factory/sessions/<encoded-path>/<session-id>.jsonl for appended events
• Parses Droid JSONL entries (session_start, message, todo_state, session_end)
• Maps entries to running / waiting / done / stale statuses using the same semantics other watchers use
• Resolves each session to its mux session via the encoded cwd in the folder name (/Users/foo/proj → -Users-foo-proj)
• Detects permission prompts (assistant tool_use + file stops growing past threshold → waiting)
• Detects stuck processes (running/waiting + no growth past threshold → stale)

Changes

• New: packages/runtime/src/agents/watchers/droid.ts (DroidAgentWatcher, 461 lines)
• New: packages/runtime/test/droid-watcher.test.ts (15 tests, all pass)
• Register and export DroidAgentWatcher from packages/runtime/src/index.ts
• Register in apps/server/src/main.ts alongside other built-in watchers
• Add droid: ["droid", "factory"] to the agent pattern map in packages/runtime/src/server/index.ts

Test plan

• bun test packages/runtime/test/droid-watcher.test.ts — 15/15 pass
• bun test packages/runtime/test — 382/382 pass (no regressions)
• Running locally in my tmux setup for ~weeks, tracks Droid sessions correctly alongside Claude Code and Codex

Happy to iterate on style, docstring placement, or the status-mapping thresholds if they should match constants elsewhere in the codebase.

[inspect-review]

inspect review

Triage: 45 entities analyzed | 0 critical, 0 high, 3 medium, 42 low
Verdict: standard_review

Findings (4)

1. [low] Mixed time bases in seed vs runtime heuristics: in seed mode toolUseSeenAt and lastGrowthAt are set to mtimeMs (filesystem timestamp), but unchanged-file heuristics compare against Date.now() (wall clock). This can cause immediate or delayed waiting/stale transitions depending on file age/clock skew. Evidence: seed set toolUseSeenAt: ... ? mtimeMs : undefined and lastGrowthAt: ... ? mtimeMs : undefined; unchanged path uses const now = Date.now(); now - prev.toolUseSeenAt and now - prev.lastGrowthAt.
2. [low] Runtime incompatibility: watcher uses Bun-specific APIs (Bun.file(...)) inside packages/runtime/src/agents/watchers/droid.ts. If runtime is executed under Node (common for server runtimes), this will throw because Bun is undefined. Evidence: text = await Bun.file(filePath).text(); and const buf = await Bun.file(filePath).arrayBuffer();.
3. [low] Incremental read is not actually incremental and can be a production perf bug: despite the comment 'only new bytes', it reads the entire file into memory every time via Bun.file(filePath).arrayBuffer() and then slices. Large/long-running JSONL sessions will cause repeated full-file reads. Evidence: // --- Incremental read: only new bytes --- followed by const buf = await Bun.file(filePath).arrayBuffer();.
4. [low] Potential unhandled promise rejection from fs.watch callbacks: processFile is async and is invoked without await/.catch() inside watch(...) handlers. If processFile ever throws (e.g., unexpected runtime error), it can surface as an unhandled rejection. Evidence: watch(dirPath, (...) => { ... this.processFile(...); }) and similarly for the sessionsDir watcher.

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Reviewed by inspect | Entity-level triage found 0 high-risk changes

[Palanikannan1437]

I've used droid in the past, awesome harness! will test this out on my end and leave feedback if needed, thanks for the PR 🙌