Decide event transitions under the completion lock

complete/uncomplete return a CompletionResult str subclass carrying
appended (decided with the write under the lock), so duplicate
concurrent calls fire one transition event; day-complete only
evaluates for an instance due today.

custom_components/nestquest/completion.py

@@ -366,6 +366,25 @@ async def instance_state(
     return _derived_state(instance, latest, today_date)
 
 
+class CompletionResult(str):
+    """The derived instance state, carrying the append verdict.
+
+    A ``str`` subclass so every existing ``result == "done"`` contract
+    keeps working; ``appended`` reports whether THIS call actually
+    appended an event (decided under the same lock as the append), so
+    a caller — the Feature 09 service path firing bus events —
+    announces a transition exactly once even under a concurrent
+    duplicate call where the loser's write is a no-op.
+    """
+
+    appended: bool
+
+    def __new__(cls, state: str, *, appended: bool) -> "CompletionResult":
+        obj = super().__new__(cls, state)
+        obj.appended = appended
+        return obj
+
+
 async def complete_instance(
     database: NestQuestDatabase,
     instance_id: int,
@@ -375,14 +394,14 @@ async def complete_instance(
     actor_child_id: int | None = None,
     now: datetime.datetime | None = None,
     today: datetime.date | None = None,
-) -> str:
+) -> CompletionResult:
     """Append a completed event unless the instance is already done.
 
-    Returns the derived state ``done``.  An already-done instance is a
-    no-op: nothing is appended.  Unknown ``instance_id`` raises
-    ValueError naming the field.  Existence, latest-event, and the
-    append run under one connection lock so a concurrent complete
-    cannot double-append.
+    Returns the derived state ``done``; ``appended`` reports whether
+    THIS call appended (False on an already-done no-op).  Unknown
+    ``instance_id`` raises ValueError naming the field.  Existence,
+    latest-event, and the append run under one connection lock so a
+    concurrent complete cannot double-append.
 
     ``was_on_time`` is computed from the HA-local completion moment
     (threaded ``now`` / ``today``) against the instance ``due_date``
@@ -404,7 +423,7 @@ async def complete_instance(
             instance_id
         )
         if latest is not None and latest.event_type == EVENT_COMPLETED:
-            return "done"
+            return CompletionResult("done", appended=False)
         if latest is not None and latest.event_type != EVENT_UNCOMPLETED:
             raise ValueError(
                 f"event_type must be '{EVENT_COMPLETED}' or "
@@ -421,7 +440,7 @@ async def complete_instance(
             was_on_time=_was_on_time(instance, now, today),
             now=now,
         )
-    return "done"
+    return CompletionResult("done", appended=True)
 
 
 async def uncomplete_instance(
@@ -433,16 +452,16 @@ async def uncomplete_instance(
     actor_child_id: int | None = None,
     now: datetime.datetime | None = None,
     today: datetime.date | None = None,
-) -> str:
+) -> CompletionResult:
     """Append an uncompleted event unless the instance is already open.
 
     Returns the derived state ``open``, or ``missed`` when the instance
-    is past due (``due_date`` before HA-local ``today``).  An
-    already-open instance is a no-op: nothing is appended.  Unknown
-    ``instance_id`` raises ValueError naming the field.  Existence,
-    latest-event, and the append run under one connection lock so a
-    concurrent uncomplete cannot double-append.  The original completed
-    row is not modified.
+    is past due (``due_date`` before HA-local ``today``); ``appended``
+    reports whether THIS call appended (False on an already-open
+    no-op).  Unknown ``instance_id`` raises ValueError naming the
+    field.  Existence, latest-event, and the append run under one
+    connection lock so a concurrent uncomplete cannot double-append.
+    The original completed row is not modified.
     """
     instance_id = _validate_int_id(instance_id, "instance_id")
     actor_source, actor_user_id, actor_child_id = _validate_actor(
@@ -459,7 +478,10 @@ async def uncomplete_instance(
             instance_id
         )
         if latest is None or latest.event_type == EVENT_UNCOMPLETED:
-            return _derived_state(instance, latest, today_date)
+            return CompletionResult(
+                _derived_state(instance, latest, today_date),
+                appended=False,
+            )
         if latest.event_type != EVENT_COMPLETED:
             raise ValueError(
                 f"event_type must be '{EVENT_COMPLETED}' or "
@@ -476,7 +498,9 @@ async def uncomplete_instance(
             was_on_time=None,
             now=now,
         )
-    return _derived_state(instance, latest, today_date)
+    return CompletionResult(
+        _derived_state(instance, latest, today_date), appended=True
+    )
 
 
 async def list_missed_for_child(