feat(agent): persist action execution state and idempotency

[05F3759DF]

Context

Keystone action requests may be delivered more than once because the reliable source of truth is the Keystone action queue and WebSocket push is only a wake-up path. Axon Agent needs local execution state so retries, reconnects, and agent restarts do not trigger duplicate script runs.

Scope

• Persist local action execution records keyed by request_id.
• Track action_id, status, queued_at, started_at, finished_at, exit_code, and error_summary.
• Treat duplicate request_id delivery as idempotent and return the existing state.
• Mark stale in-flight executions consistently after agent restart.
• Respect action request expiration time and avoid starting expired requests.

Acceptance Criteria

• Re-delivering the same request_id does not execute the action twice.
• Agent restart preserves completed and failed execution state.
• Expired requests are reported as expired and are not executed.
• Local state can be inspected for operator diagnostics.
• Tests cover duplicate request delivery, restart recovery, expired request handling, and completed/failed state persistence.

Depends On

• feat(agent): add local action registry for pre-registered ops scripts #90
• feat(agent): execute allowlisted action requests safely #91

Related

• feat(ops): create action request API with audit trail keystone#66
• feat(ops): expose action execution status and logs keystone#67