Observe claimed prepared executions

docs/roadmap/implementation.md

@@ -407,6 +407,8 @@ guidance for ordinary observations only; run root and internal race tests; commi
 
 ## Stage 9 — Observe Prepared Execution Without Weakening Its Lifecycle
 
+**Completed:** 2026-09-23.
+
 Retain the adapted observer with the effective retries in the private prepared
 payload. Claim atomically before starting observation, release the claim mutex,
 install payload cleanup, then emit started. Preparation emits nothing; successful