multi-agent-watch

multi-agent-watch

Claude Code plugin that detects when multiple Claude Code sessions are working on the same repository concurrently — and lets them coordinate: each session publishes a one-line self-summary of what it's doing, and you can leave direct messages for another running session.

What it does

Collision detection

• Registers each Claude Code session in ~/.claude/state/multi-agent-watch/sessions/<session-id>.json.
• On SessionStart, scans the registry for other active sessions on the same repo (resolved via git rev-parse --show-toplevel, falling back to absolute cwd for non-git directories).
• If a collision is found:
  • Banner printed to stderr (visible in your terminal).
  • Desktop notification (terminal-notifier → osascript → notify-send, whichever is available).
  • Context injected into the new session so Claude knows other agents are active and can edit defensively.
  • systemMessage shown by Claude Code's own UI.
• monitor (on UserPromptSubmit + PostToolUse) heartbeats and injects a delta whenever the set of other sessions changes (who joined / who left).
• Stop refreshes the heartbeat. Stale entries (>10 min since last heartbeat) are auto-purged on every hook fire. SessionEnd removes the entry immediately.

Self-summary (what each session is doing)

• On Stop, an async hook (summarize.sh) runs claude -p --model haiku over a digest of the session's transcript and stores a one-sentence summary in the session's registry entry.
• It is run-once by default: the model call fires a single time per session (guarded by an atomic lock + a cached summary field). Set MW_SUMMARY_REFRESH=1 to instead refresh the summary on every Stop as the work evolves.
• The call is async, so it never blocks your turn, and it's detached from your context — the spawned claude is marked (MW_SUMMARY_CHILD) so it doesn't recurse into these hooks.
• Other sessions read that summary: collision banners and monitor deltas show each sibling's doing: … line. N sessions ⇒ N summary calls total (each summarizes itself), not N².

Direct messages (留言)

• /mw-send <session-id-prefix | all> <message> leaves a note for another active session on the same repo.
• The recipient's monitor hook delivers the message (and deletes it) into its context on its next prompt or tool use.
• all broadcasts to every other session on your repo (you are excluded). A prefix targets specific session(s).
• Sender identity comes from $CLAUDE_CODE_SESSION_ID.

Subscriptions (watch a session)

• /mw-watch <session-id-prefix> subscribes you to another session. While subscribed you get a message (delivered through the same monitor drain) when that session changes its self-summary or ends.
• /mw-watch --list shows who you're watching; /mw-watch --stop <prefix> unsubscribes.
• Watchers are stored on the watched session's entry and fan out on summary-change / removal (including stale-purge). Subscriptions auto-clear on SessionEnd and dead watchers are pruned lazily.
• Turns polling into push — e.g. waiting for a sibling to finish a prerequisite instead of re-reading a coordination file.

Install

This plugin ships via a local directory marketplace. The source lives in your plugins-local directory and is installed into the Claude Code plugin cache; enable it with multi-agent-watch@local in ~/.claude/settings.json (enabledPlugins). Restart Claude Code (or /plugin) to reload. Hooks are auto-registered from hooks/hooks.json.

Slash commands

• /mw-status — list all registered sessions grouped by repo, flagging collisions; shows each session's self-summary, watcher count, and any pending (undelivered) messages.
• /mw-send <to> <message> — leave a message for another session (<to> is an 8-char session-id prefix or all).
• /mw-watch <to> / /mw-watch --list / /mw-watch --stop <to> — subscribe to a session's summary-change / end events.

Config (env vars)