State correctness: unexpected-transition telemetry and anomaly alerts

[mark-e-deyoung]

Summary

Add unexpected-transition telemetry and alert signals for lifecycle/control/UI state transitions.

Why

When transitions occur outside expected paths, operators need first-class observability to diagnose correctness issues quickly.

Scope

• Emit structured "unexpected_transition" events with:
  • previous state, requested transition, resulting state
  • API endpoint/method source
  • session_id and instance mode context
• Add counters/metrics for transition anomalies.
• Expose recent anomalies in diagnostics bundle and/or /lifecycle/events summaries.
• Add tests covering anomaly emission on blocked/invalid transitions.

Acceptance Criteria

• Unexpected transitions are observable via logs/metrics.
• Diagnostics surfaces anomaly counts and recent events.
• Tests verify emission on representative invalid transition paths.