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
+is rejected. A command whose requested lifecycle state already holds is also
-except for the deliberately auditable `decided` → `decided` action.
+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

src/govoplan_poll/backend/router.py

@@ -100,8 +100,12 @@ def _poll_response(poll) -> PollResponse:
 def _transition_status_response(result) -> PollStatusResponse:
     return PollStatusResponse(
         poll=_poll_response(result.poll),
-        transition=PollLifecycleTransitionResponse.model_validate(
+        transition=(
+            PollLifecycleTransitionResponse.model_validate(
                 poll_lifecycle_transition_response(result.transition)
+            )
+            if result.transition is not None
+            else None
         ),
         replayed=result.replayed,
     )

src/govoplan_poll/backend/service.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import hashlib
+import logging
 import re
 import secrets
 from dataclasses import dataclass
@@ -24,6 +25,9 @@ from govoplan_poll.backend.schemas import (
 from govoplan_poll.backend.transitions import DEFAULT_POLL_TRANSITION_ENGINE, PollTransitionEngine
 
 
+logger = logging.getLogger("govoplan.poll.lifecycle")
+
+
 class PollError(ValueError):
     pass
 
@@ -67,7 +71,7 @@ YES_NO_MAYBE_OPTIONS = (
 @dataclass(frozen=True)
 class PollTransitionResult:
     poll: Poll
-    transition: PollLifecycleTransition
+    transition: PollLifecycleTransition | None
     replayed: bool = False
 
 
@@ -721,6 +725,77 @@ def _replayed_transition(
     return PollTransitionResult(poll=poll, transition=existing, replayed=True)
 
 
+def _latest_lifecycle_transition(
+    session: Session,
+    *,
+    poll_id: str,
+) -> PollLifecycleTransition | None:
+    return (
+        session.query(PollLifecycleTransition)
+        .filter(PollLifecycleTransition.poll_id == poll_id)
+        .order_by(
+            PollLifecycleTransition.created_at.desc(),
+            PollLifecycleTransition.id.desc(),
+        )
+        .first()
+    )
+
+
+def _is_exact_transition_noop(
+    session: Session,
+    *,
+    poll: Poll,
+    action: str,
+    decision_option: PollOption | None,
+    transition_engine: PollTransitionEngine,
+) -> bool:
+    """Recognize commands whose requested lifecycle state already holds."""
+
+    rule = transition_engine.policy.rules.get(action)
+    if rule is None:
+        return False
+    if action == "decide":
+        return (
+            rule.target_status == poll.status
+            and decision_option is not None
+            and decision_option.id == poll.decided_option_id
+        )
+    if rule.restore_archived_status:
+        latest = _latest_lifecycle_transition(session, poll_id=poll.id)
+        return (
+            latest is not None
+            and latest.action == action
+            and latest.to_status == poll.status
+        )
+    return rule.target_status == poll.status
+
+
+def _log_duplicate_transition(
+    *,
+    poll: Poll,
+    action: str,
+    actor_user_id: str | None,
+    actor_api_key_id: str | None,
+    reason: str,
+    has_idempotency_key: bool,
+) -> None:
+    """Record command duplication as operational telemetry, not lifecycle audit."""
+
+    logger.info(
+        "Ignored repeated exact Poll lifecycle transition",
+        extra={
+            "event": "poll.lifecycle_transition.duplicate",
+            "tenant_id": poll.tenant_id,
+            "poll_id": poll.id,
+            "transition_action": action,
+            "actor_user_id": actor_user_id,
+            "actor_api_key_id": actor_api_key_id,
+            "duplicate_reason": reason,
+            "has_idempotency_key": has_idempotency_key,
+        },
+    )
+
+
 def _clear_expired_close_for_open(poll: Poll, *, action: str, now: datetime) -> datetime | None:
     if action != "open" or poll.closes_at is None:
         return None
@@ -793,7 +868,7 @@ def transition_poll(
     mutation_owner: PollMutationOwner | None = None,
     transition_engine: PollTransitionEngine = DEFAULT_POLL_TRANSITION_ENGINE,
 ) -> PollTransitionResult:
-    """Apply one policy-controlled transition and append its durable audit record."""
+    """Apply a policy transition, or return an audit-free exact no-op."""
 
     poll = _lock_poll_for_transition(session, tenant_id=tenant_id, poll_id=poll_id)
     _assert_poll_mutation_owner(poll, mutation_owner=mutation_owner)
@@ -817,8 +892,33 @@ def transition_poll(
         decision_option=decision_option,
     )
     if replayed is not None:
+        _log_duplicate_transition(
+            poll=poll,
+            action=action,
+            actor_user_id=actor_user_id,
+            actor_api_key_id=actor_api_key_id,
+            reason="idempotency_key_replay",
+            has_idempotency_key=True,
+        )
         return replayed
 
+    if _is_exact_transition_noop(
+        session,
+        poll=poll,
+        action=action,
+        decision_option=decision_option,
+        transition_engine=transition_engine,
+    ):
+        _log_duplicate_transition(
+            poll=poll,
+            action=action,
+            actor_user_id=actor_user_id,
+            actor_api_key_id=actor_api_key_id,
+            reason="requested_state_already_active",
+            has_idempotency_key=normalized_key is not None,
+        )
+        return PollTransitionResult(poll=poll, transition=None, replayed=True)
+
     try:
         plan = transition_engine.plan(
             current_status=poll.status,

tests/test_lifecycle.py

@@ -266,12 +266,86 @@ class PollLifecycleTests(unittest.TestCase):
                 idempotency_key="decision-2",
             )
 
-    def test_repeated_exact_transition_without_an_identity_is_rejected(self) -> None:
+    def test_repeated_exact_transition_without_an_identity_is_an_audit_free_noop(self) -> None:
+        poll = self._poll()
+        applied = transition_poll(self.session, tenant_id="tenant-1", poll_id=poll.id, action="open")
+
+        with self.assertLogs("govoplan.poll.lifecycle", level="INFO") as logs:
+            repeated = transition_poll(
+                self.session,
+                tenant_id="tenant-1",
+                poll_id=poll.id,
+                action="open",
+                actor_user_id="owner",
+            )
+
+        self.assertFalse(applied.replayed)
+        self.assertTrue(repeated.replayed)
+        self.assertIsNone(repeated.transition)
+        self.assertEqual(poll.status, "open")
+        self.assertEqual(len(poll.lifecycle_transitions), 1)
+        self.assertIn("Ignored repeated exact Poll lifecycle transition", logs.output[0])
+
+    def test_same_decision_is_a_noop_but_a_changed_decision_is_audited(self) -> None:
         poll = self._poll()
         transition_poll(self.session, tenant_id="tenant-1", poll_id=poll.id, action="open")
+        transition_poll(self.session, tenant_id="tenant-1", poll_id=poll.id, action="close")
+        first = transition_poll(
+            self.session,
+            tenant_id="tenant-1",
+            poll_id=poll.id,
+            action="decide",
+            option_key="yes",
+        )
+        repeated = transition_poll(
+            self.session,
+            tenant_id="tenant-1",
+            poll_id=poll.id,
+            action="decide",
+            option_key="yes",
+        )
+        changed = transition_poll(
+            self.session,
+            tenant_id="tenant-1",
+            poll_id=poll.id,
+            action="decide",
+            option_key="no",
+        )
 
+        self.assertTrue(repeated.replayed)
+        self.assertIsNone(repeated.transition)
+        self.assertIsNotNone(first.transition)
+        self.assertIsNotNone(changed.transition)
+        self.assertEqual(changed.transition.previous_decision_option_id, first.transition.decision_option_id)
+        self.assertEqual(
+            [item.action for item in poll.lifecycle_transitions],
+            ["open", "close", "decide", "decide"],
+        )
+
+    def test_exact_unarchive_retry_is_a_noop_but_unarchive_without_history_is_invalid(self) -> None:
+        poll = self._poll()
+        transition_poll(self.session, tenant_id="tenant-1", poll_id=poll.id, action="archive")
+        transition_poll(self.session, tenant_id="tenant-1", poll_id=poll.id, action="unarchive")
+
+        repeated = transition_poll(
+            self.session,
+            tenant_id="tenant-1",
+            poll_id=poll.id,
+            action="unarchive",
+        )
+
+        self.assertTrue(repeated.replayed)
+        self.assertIsNone(repeated.transition)
+        self.assertEqual([item.action for item in poll.lifecycle_transitions], ["archive", "unarchive"])
+
+        never_archived = self._poll(title="Never archived")
         with self.assertRaisesRegex(PollError, "not allowed"):
-            transition_poll(self.session, tenant_id="tenant-1", poll_id=poll.id, action="open")
+            transition_poll(
+                self.session,
+                tenant_id="tenant-1",
+                poll_id=never_archived.id,
+                action="unarchive",
+            )
 
     def test_archive_and_unarchive_restore_status_and_append_audit_history(self) -> None:
         poll = self._poll()
@@ -444,6 +518,7 @@ class PollLifecycleTests(unittest.TestCase):
         self.assertEqual(opened.poll.status, "open")
         self.assertFalse(opened.replayed)
         self.assertTrue(replay.replayed)
+        self.assertIsNotNone(replay.transition)
         self.assertEqual(len(lifecycle.history), 1)
         self.assertEqual(lifecycle.history[0].actor_user_id, "owner-membership")
         self.assertEqual(
@@ -462,6 +537,27 @@ class PollLifecycleTests(unittest.TestCase):
             )
         self.assertEqual(rejected.exception.status_code, 400)
 
+    def test_generic_api_returns_null_transition_for_domain_noop(self) -> None:
+        poll = self._poll(status="open", title="Already open")
+
+        repeated = api_transition_poll(
+            poll.id,
+            PollTransitionRequest(action="open"),
+            idempotency_key=None,
+            session=self.session,
+            principal=self._principal(),
+        )
+
+        self.assertEqual(repeated.poll.status, "open")
+        self.assertTrue(repeated.replayed)
+        self.assertIsNone(repeated.transition)
+        self.assertEqual(
+            self.session.query(PollLifecycleTransition)
+            .filter(PollLifecycleTransition.poll_id == poll.id)
+            .count(),
+            0,
+        )
+
 
 if __name__ == "__main__":
     unittest.main()