fix(alarms): give up after three runs without delivery (FLAW-12)

New column alarm_failures counts ticker runs in which no channel
delivered; at three the alarm is marked as done and a warning is logged
instead of retrying every minute forever. Success, a new due date or
reopening the task starts over with three attempts.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/storage/recurrence_test.go

@@ -138,3 +138,50 @@ func TestAlarmResetsOnNewDueDateOrReopen(t *testing.T) {
 		t.Errorf("reopening must re-arm the alarm")
 	}
 }
+
+func TestAlarmGivesUpAfterThreeFailedRuns(t *testing.T) {
+	store, err := NewStore(filepath.Join(t.TempDir(), "alarmfail.db"))
+	if err != nil {
+		t.Fatalf("NewStore: %v", err)
+	}
+	defer store.Close()
+	u, _ := store.CreateUser("anna@example.com", "hash", "Anna", "member")
+	task, _ := store.CreateThoughtWithDetails(u.ID, "Webhook kaputt", "normal", "manual", "2026-10-30", "", "todo", "")
+	_, _ = store.UpdateThoughtTriage(u.ID, task.ID, "keep", "task", "", "", "")
+	pending := func() bool {
+		alarms, _ := store.GetDueTasksForAlarm()
+		for _, a := range alarms {
+			if a.TaskID == task.ID {
+				return true
+			}
+		}
+		return false
+	}
+
+	for run := 1; run <= MaxAlarmFailures; run++ {
+		gaveUp, err := store.RecordTaskAlarmFailure(task.ID)
+		if err != nil {
+			t.Fatalf("run %d: %v", run, err)
+		}
+		if gaveUp != (run == MaxAlarmFailures) || pending() == (run == MaxAlarmFailures) {
+			t.Fatalf("run %d: gaveUp=%v pending=%v", run, gaveUp, pending())
+		}
+	}
+
+	// A new due date gets three fresh attempts
+	later := "2026-11-02"
+	_, _ = store.UpdateThoughtDetails(u.ID, task.ID, nil, nil, &later, nil, nil, nil, nil, nil, nil)
+	if !pending() {
+		t.Fatalf("new due date must re-arm the alarm")
+	}
+	if gaveUp, _ := store.RecordTaskAlarmFailure(task.ID); gaveUp {
+		t.Errorf("failure counter must start over after a new due date")
+	}
+	// Success clears the counter
+	_ = store.MarkTaskAlarmSent(task.ID)
+	var failures int
+	_ = store.db.QueryRow(`SELECT alarm_failures FROM thoughts WHERE id = ?`, task.ID).Scan(&failures)
+	if failures != 0 {
+		t.Errorf("successful alarm should reset failures, got %d", failures)
+	}
+}