feat: replay and observe principal-scoped Astrid bus activity

Outcome

Let the detached shell replay and then observe principal-scoped Astrid bus activity through a bounded descriptive lens suitable for agents and people.

Scope and ownership

Recorded sanitized fixtures, replay clock, live read-only bridge, WIT/interface descriptions, activity correlation, backpressure, reconnect, and privacy-aware inspection. The shell receives only what its principal may observe.

Dependencies

• Surface Model and detached shell.
• Astrid substrate gap audit.

Exit gate

The same activity can run against a deterministic trace and a live read-only principal connection; reconnect and overflow trigger bounded resynchronization; cross-principal events never appear; descriptions remain data and cannot mint actions.

Claim boundary

Observation is not authorization, broad bus enumeration, arbitrary debugging access, or governed action execution.

Verification

Replay/live parity, overflow and reconnect tests, cross-principal denial, redaction audit, malformed description handling, and bounded-memory evidence.