Add calendar cache layer, incremental sync tests, completion assertions

- Google Calendar events now cached via CacheFetcher pattern with
  stale-cache fallback on API errors (new migration 015, store methods,
  fetchCalendarEvents handler, BuildTimeline reads from store)
- Todoist incremental sync path covered by 5 new tests
- Task completion tests assert response body, headers, and template data

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

1 files changed, 18 insertions, 5 deletions

diff --git a/internal/handlers/handlers.go b/internal/handlers/handlers.go
index 876326e..e06c35e 100644
--- a/internal/handlers/handlers.go
+++ b/internal/handlers/handlers.go
@@ -267,7 +267,7 @@ func (h *Handler) aggregateData(ctx context.Context, forceRefresh bool) (*models
 
 	if h.googleCalendarClient != nil {
 		fetch("Google Calendar", func() error {
-			events, err := h.googleCalendarClient.GetUpcomingEvents(ctx, 10)
+			events, err := h.fetchCalendarEvents(ctx, false)
 			if err == nil {
 				mu.Lock()
 				data.Events = events
@@ -450,6 +450,22 @@ func (h *Handler) fetchMeals(ctx context.Context, forceRefresh bool) ([]models.M
 	return fetcher.FetchWithCache(ctx, forceRefresh)
 }
 
+// fetchCalendarEvents fetches Google Calendar events from cache or API
+func (h *Handler) fetchCalendarEvents(ctx context.Context, forceRefresh bool) ([]models.CalendarEvent, error) {
+	if h.googleCalendarClient == nil {
+		return nil, nil
+	}
+	fetcher := &CacheFetcher[models.CalendarEvent]{
+		Store:        h.store,
+		CacheKey:     store.CacheKeyGoogleCalendar,
+		TTLMinutes:   h.config.CacheTTLMinutes,
+		Fetch:        func(ctx context.Context) ([]models.CalendarEvent, error) { return h.googleCalendarClient.GetUpcomingEvents(ctx, 50) },
+		GetFromCache: h.store.GetCalendarEvents,
+		SaveToCache:  h.store.SaveCalendarEvents,
+	}
+	return fetcher.FetchWithCache(ctx, forceRefresh)
+}
+
 // fetchBoards fetches Trello boards from cache or API
 func (h *Handler) fetchBoards(ctx context.Context, forceRefresh bool) ([]models.Board, error) {
 	fetcher := &CacheFetcher[models.Board]{
@@ -999,10 +1015,7 @@ func (h *Handler) HandleTabPlanning(w http.ResponseWriter, r *http.Request) {
 	boards, _ := h.store.GetBoards()
 	tasks, _ := h.store.GetTasks()
 
-	var events []models.CalendarEvent
-	if h.googleCalendarClient != nil {
-		events, _ = h.googleCalendarClient.GetUpcomingEvents(r.Context(), 20)
-	}
+	events, _ := h.fetchCalendarEvents(r.Context(), false)
 
 	var scheduled []ScheduledItem
 	var unscheduled []models.Atom