feat(poll): make exact transitions idempotent

README.md

@@ -169,8 +169,13 @@ metadata. Every applied transition has a Poll-owned lifecycle audit record.
 Re-deciding always appends a record and supersedes the current decision. An
 exact retry carrying the same `Idempotency-Key` is a no-op and returns the
 original transition record; reusing that key for a different action or option
-is rejected. Without an idempotency identity, a repeated transition is invalid
-except for the deliberately auditable `decided` → `decided` action.
+is rejected. A command whose requested lifecycle state already holds is also
+an idempotent domain no-op, even without an idempotency identity. It returns
+the current Poll with `replayed=true` and `transition=null`, does not append a
+lifecycle audit record, and is emitted only to operational logs as duplicate
+command telemetry. A new idempotency key supplied for such an audit-free no-op
+is not consumed. Re-deciding with a different option remains a new auditable
+action; repeating the current decision is a no-op.
 
 Poll API representations expose every lifecycle action with its availability
 and, when unavailable, the policy reason. Management clients can use the