Add 5 pi extensions: pi-subagents, pi-crew, rpiv-pi, pi-interactive-shell, pi-intercom

extensions/pi-crew/docs/live-mailbox-runtime.md

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+# Live Mailbox Runtime Direction
+
+`pi-crew` currently uses workflow child-process orchestration: a run materializes tasks, executes them through the scheduler, writes artifacts/events, and optionally launches child Pi workers.
+
+A full live mailbox runtime is intentionally out of scope for the current stable surface. Current foundational mailbox files are intentionally simple and local:
+
+```text
+{stateRoot}/mailbox/inbox.jsonl
+{stateRoot}/mailbox/outbox.jsonl
+{stateRoot}/mailbox/delivery.json
+{stateRoot}/mailbox/tasks/{taskId}/inbox.jsonl
+{stateRoot}/mailbox/tasks/{taskId}/outbox.jsonl
+```
+
+They are exposed through safe API operations (`read-mailbox`, `send-message`, `ack-message`, `read-delivery`, `validate-mailbox`) but do not yet imply always-on long-lived workers. If a full runtime is added later, it should build on the foundations already present:
+
+- `src/state/contracts.ts` for status/event contracts
+- `src/state/task-claims.ts` for claim/lease safety
+- `src/runtime/worker-heartbeat.ts` for liveness
+- `src/state/locks.ts` for run-level mutation safety
+- `action: "api"` for safe interop boundaries
+
+## Proposed phases
+
+1. **Read-only interop** — already started with `api` operations.
+2. **Heartbeat writers** — allow workers to update heartbeat/progress safely.
+3. **Claim-safe task lifecycle** — expose claim/release/transition operations with tokens.
+4. **Mailbox** — add worker inbox/leader inbox files and delivery state.
+5. **Live workers** — only after the above contracts are stable.
+
+## Non-goals for now
+
+- No always-on background worker pool.
+- No automatic destructive cleanup of dirty worktrees.
+- No recursive team spawning by workers.
+- No mailbox mutation without locks and schema validation.