fix timers

backend/app/api/routes_timer.py

@@ -63,11 +63,18 @@ def resume(session: DbSession, settings: Settings) -> dict:
 @router.post("/complete")
 def complete(body: CompleteTimerRequest, session: DbSession, settings: Settings) -> dict:
     try:
-        finished, follow_on = pomodoro.complete(session, settings, auto_next=body.auto_next)
+        finished, follow_on = pomodoro.complete(
+            session,
+            settings,
+            auto_next=body.auto_next,
+            expect_id=body.session_id,
+        )
     except pomodoro.TimerError as exc:
         raise HTTPException(status_code=400, detail=str(exc)) from exc
 
-    celebration = _maybe_celebrate(session, settings) if finished.is_work else None
+    # `finished` is None when the named interval was no longer the running one:
+    # nothing happened, so there is nothing to celebrate and nothing to announce.
+    celebration = _maybe_celebrate(session, settings) if finished and finished.is_work else None
     state = pomodoro.state(session, settings)
     state["finished"] = pomodoro.session_dict(finished)
     state["auto_started"] = pomodoro.session_dict(follow_on)

backend/app/api/schemas.py

@@ -29,6 +29,16 @@ class AttachTaskRequest(BaseModel):
 
 class CompleteTimerRequest(BaseModel):
     auto_next: bool = True
+    session_id: int | None = None
+    """Which interval the client believes it is finishing.
+
+    Every client ticks its own local countdown and calls `complete` when it
+    reaches zero, so with two of them open (the phone and the desktop, say)
+    both fire within the same second. Unconditionally, the second call lands
+    on whatever `auto_next` has just started and ends *that* — which is why a
+    break could vanish the instant it began. Sent along, a stale call is a
+    no-op instead. Omitted, the old unconditional behaviour stands.
+    """
 
 
 class TaskCreateRequest(BaseModel):