feat(tasks): due dates with optional time; alarms at the right moment

Due dates can carry a time (YYYY-MM-DDTHH:MM). Alarms fire at that time,
or 09:00 for all-day tasks, minus the user's lead time, in TZ (default
Europe/Berlin, tzdata embedded). A new due date or reopening a task
re-arms the alarm. Recurrence keeps the time; Markdown export/import
carry it. The UI shows relative labels ("Heute, 14:30"), marks overdue
tasks to the minute and groups by local day instead of the UTC date.

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

internal/storage/export_markdown.go

@@ -141,7 +141,8 @@ func taskMarkdownLine(t domain.Thought) string {
 		line += " 🔁 every " + every
 	}
 	if t.DueDate != "" {
-		line += " 📅 " + t.DueDate
+		// Obsidian Tasks only knows the date; the time follows separated by a space
+		line += " 📅 " + strings.Replace(t.DueDate, "T", " ", 1)
 	}
 	var sb strings.Builder
 	sb.WriteString(line + "\n")

internal/storage/import_markdown.go

@@ -759,7 +759,7 @@ func MarkdownToBlocks(md string) []domain.DocumentBlock {
 
 var (
 	recurRe    = regexp.MustCompile(`(?i)[ \t]*🔁[ \t]*every[ \t]+(day|week|month|year)\b`)
-	dueRe      = regexp.MustCompile(`[ \t]*📅[ \t]*(\d{4}-\d{2}-\d{2})`)
+	dueRe      = regexp.MustCompile(`[ \t]*📅[ \t]*(\d{4}-\d{2}-\d{2})(?:[ T](\d{2}:\d{2}))?`)
 	priorityRe = regexp.MustCompile(`[ \t]*(🔺|⏫|🔼|🔽|⏬)`)
 )
 
@@ -801,6 +801,9 @@ func parseTaskFile(body string) []importTask {
 		}
 		if d := dueRe.FindStringSubmatch(t.content); d != nil {
 			t.due = d[1]
+			if d[2] != "" {
+				t.due += "T" + d[2]
+			}
 			t.content = dueRe.ReplaceAllString(t.content, "")
 		}
 		if p := priorityRe.FindStringSubmatch(t.content); p != nil {

internal/storage/recurrence.go

@@ -18,12 +18,14 @@ func validRecurrence(r string) bool {
 	return false
 }
 
-// NextDueDate moves a due date (YYYY-MM-DD, or today when empty) one interval forward. Months and years
-// keep the day where possible and fall back to the month's last day (31 Jan -> 28/29 Feb).
+// NextDueDate moves a due date (YYYY-MM-DD or YYYY-MM-DDTHH:MM, today when empty) one interval forward
+// and keeps the time. Months and years keep the day where possible and fall back to the month's last
+// day (31 Jan -> 28/29 Feb).
 func NextDueDate(due, rule string, today time.Time) string {
-	base, err := time.Parse("2006-01-02", due)
-	if err != nil {
-		base = time.Date(today.Year(), today.Month(), today.Day(), 0, 0, 0, 0, time.UTC)
+	parsed, hasTime, ok := domain.ParseDue(due, time.UTC)
+	base := time.Date(today.Year(), today.Month(), today.Day(), 0, 0, 0, 0, time.UTC)
+	if ok {
+		base = time.Date(parsed.Year(), parsed.Month(), parsed.Day(), 0, 0, 0, 0, time.UTC)
 	}
 	switch rule {
 	case "daily":
@@ -35,6 +37,9 @@ func NextDueDate(due, rule string, today time.Time) string {
 	case "yearly":
 		base = addMonthsClamped(base, 12)
 	}
+	if hasTime {
+		return base.Format("2006-01-02") + parsed.Format("T15:04")
+	}
 	return base.Format("2006-01-02")
 }
 

internal/storage/recurrence_test.go

@@ -17,6 +17,8 @@ func TestNextDueDate(t *testing.T) {
 		{"2026-03-15", "monthly", "2026-04-15"},
 		{"2028-02-29", "yearly", "2029-02-28"},
 		{"", "weekly", "2026-11-05"},
+		{"2026-01-31T07:15", "monthly", "2026-02-28T07:15"},
+		{"2026-10-30T23:30", "daily", "2026-10-31T23:30"},
 	}
 	for _, c := range cases {
 		if got := NextDueDate(c.due, c.rule, today); got != c.want {
@@ -95,3 +97,44 @@ func TestRepeatingTaskSpawnsItsSuccessorOnce(t *testing.T) {
 		t.Errorf("non-repeating task must not spawn")
 	}
 }
+
+func TestAlarmResetsOnNewDueDateOrReopen(t *testing.T) {
+	store, err := NewStore(filepath.Join(t.TempDir(), "alarm.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, "Zahnarzt", "normal", "manual", "2026-10-30 14:30", "", "todo", "")
+	_, _ = store.UpdateThoughtTriage(u.ID, task.ID, "keep", "task", "", "", "")
+	sent := func() bool {
+		th, _ := store.GetThoughtByID(u.ID, task.ID)
+		return th.AlarmSent
+	}
+	if th, _ := store.GetThoughtByID(u.ID, task.ID); th.DueDate != "2026-10-30T14:30" {
+		t.Fatalf("due date not normalized: %q", th.DueDate)
+	}
+
+	_ = store.MarkTaskAlarmSent(task.ID)
+	same := "2026-10-30T14:30"
+	_, _ = store.UpdateThoughtDetails(u.ID, task.ID, nil, nil, &same, nil, nil, nil, nil, nil, nil)
+	if !sent() {
+		t.Errorf("unchanged due date must not re-arm the alarm")
+	}
+	later := "2026-10-31T08:00"
+	_, _ = store.UpdateThoughtDetails(u.ID, task.ID, nil, nil, &later, nil, nil, nil, nil, nil, nil)
+	if sent() {
+		t.Errorf("new due date must re-arm the alarm")
+	}
+
+	_ = store.MarkTaskAlarmSent(task.ID)
+	done, open := true, false
+	_, _ = store.UpdateThoughtDetails(u.ID, task.ID, nil, &done, nil, nil, nil, nil, nil, nil, nil)
+	if !sent() {
+		t.Errorf("completing keeps the flag")
+	}
+	_, _ = store.UpdateThoughtDetails(u.ID, task.ID, nil, &open, nil, nil, nil, nil, nil, nil, nil)
+	if sent() {
+		t.Errorf("reopening must re-arm the alarm")
+	}
+}

internal/storage/sqlite.go

@@ -867,6 +867,7 @@ func (s *Store) CreateThought(userID, content, priority, source, dueDate string)
 
 func (s *Store) CreateThoughtWithDetails(userID, content, priority, source, dueDate, taskListID, kanbanStatus, notes string) (*domain.Thought, error) {
 	content = strings.TrimSpace(content)
+	dueDate = domain.NormalizeDue(dueDate)
 	if content == "" {
 		return nil, errors.New("content cannot be empty")
 	}
@@ -1098,8 +1099,9 @@ func (s *Store) ReorderTasks(taskListID string, items []domain.ThoughtReorderIte
 				}
 			}
 			_, err = tx.Exec(
-				`UPDATE thoughts SET sort_order = ?, kanban_status = ?, is_completed = ? WHERE id = ?`,
-				it.SortOrder, *it.KanbanStatus, isCompleted, it.ID,
+				`UPDATE thoughts SET sort_order = ?, kanban_status = ?, is_completed = ?,
+				 alarm_sent = CASE WHEN ? = 0 THEN 0 ELSE alarm_sent END WHERE id = ?`,
+				it.SortOrder, *it.KanbanStatus, isCompleted, isCompleted, it.ID,
 			)
 		} else {
 			_, err = tx.Exec(
@@ -1132,6 +1134,7 @@ func (s *Store) UpdateThoughtTriage(userID, thoughtID, action, convertTo, target
 	newStatus := domain.StatusKept
 	convertedType := thought.ConvertedType
 	convertedRefID := thought.ConvertedRefID
+	dueDate = domain.NormalizeDue(dueDate)
 	if dueDate == "" {
 		dueDate = thought.DueDate
 	}
@@ -1194,7 +1197,7 @@ func (s *Store) UpdateThoughtTriage(userID, thoughtID, action, convertTo, target
 			}
 			var metaItems []string
 			if thought.DueDate != "" {
-				metaItems = append(metaItems, "Fällig: "+thought.DueDate)
+				metaItems = append(metaItems, "Fällig: "+domain.HumanDue(thought.DueDate))
 			}
 			if thought.Priority != "" && thought.Priority != "normal" {
 				metaItems = append(metaItems, "Priorität: "+thought.Priority)
@@ -1233,9 +1236,10 @@ func (s *Store) UpdateThoughtTriage(userID, thoughtID, action, convertTo, target
 
 	_, err = s.db.Exec(
 		`UPDATE thoughts
-		 SET status = ?, converted_type = ?, converted_ref_id = ?, due_date = ?, task_list_id = ?, triaged_at = ?
+		 SET status = ?, converted_type = ?, converted_ref_id = ?, due_date = ?, task_list_id = ?, triaged_at = ?,
+		     alarm_sent = CASE WHEN due_date != ? THEN 0 ELSE alarm_sent END
 		 WHERE id = ? AND user_id = ?`,
-		string(newStatus), convertedType, convertedRefID, dueDate, taskListID, now, thoughtID, userID,
+		string(newStatus), convertedType, convertedRefID, dueDate, taskListID, now, dueDate, thoughtID, userID,
 	)
 	if err != nil {
 		return nil, err
@@ -1253,6 +1257,7 @@ func (s *Store) UpdateThoughtDetails(userID, thoughtID string, content *string,
 		return nil, err
 	}
 	wasCompleted := thought.IsCompleted
+	oldDue := thought.DueDate
 	if err := s.ensureTaskListWritable(userID, thought.TaskListID); err != nil {
 		return nil, err
 	}
@@ -1278,7 +1283,7 @@ func (s *Store) UpdateThoughtDetails(userID, thoughtID string, content *string,
 		}
 	}
 	if dueDate != nil {
-		thought.DueDate = *dueDate
+		thought.DueDate = domain.NormalizeDue(*dueDate)
 	}
 	if priority != nil {
 		p := strings.ToLower(strings.TrimSpace(*priority))
@@ -1321,6 +1326,11 @@ func (s *Store) UpdateThoughtDetails(userID, thoughtID string, content *string,
 	if err != nil {
 		return nil, err
 	}
+	// A new due date or a reopened task gets its alarm again
+	if thought.DueDate != oldDue || (wasCompleted && !thought.IsCompleted) {
+		_, _ = s.db.Exec(`UPDATE thoughts SET alarm_sent = 0 WHERE id = ?`, thoughtID)
+		thought.AlarmSent = false
+	}
 	if taskListID != nil {
 		s.PruneTaskAssignees()
 		thought.Assignees = s.getTaskAssignees(thoughtID)
@@ -3967,7 +3977,8 @@ func (s *Store) SyncTaskFromBlockCheck(userID, taskID string, checked bool) {
 		doneInt = 1
 		kanban = "done"
 	}
-	res, _ := s.db.Exec(`UPDATE thoughts SET is_completed = ?, kanban_status = ? WHERE id = ? AND user_id = ? AND is_completed != ?`, doneInt, kanban, taskID, userID, doneInt)
+	res, _ := s.db.Exec(`UPDATE thoughts SET is_completed = ?, kanban_status = ?, alarm_sent = CASE WHEN ? = 0 THEN 0 ELSE alarm_sent END
+		 WHERE id = ? AND user_id = ? AND is_completed != ?`, doneInt, kanban, doneInt, taskID, userID, doneInt)
 	if checked && res != nil {
 		if n, _ := res.RowsAffected(); n > 0 {
 			s.spawnNextOccurrence(taskID)