refactor(calendar): simplify preset handler and reuse storage util

- Extract hardcoded trending snapshot source/window to named constants.
- Collapse the three identical personal-preset nil-checks into one case.
- Persist the selected preset through the shared storage util (try/catch
  wrapped) instead of raw localStorage with manual SSR guards.
- Derive KNOWN_FILTERS from PRESET_OPTIONS so the lists can't drift.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/api/handlers/calendar.go

@@ -45,6 +45,13 @@ const (
 	calendarFilterTrending   = "trending"
 )
 
+// The Trending preset reads this canonical external-trending snapshot
+// (see internal/sections trending snapshots).
+const (
+	calendarTrendingSnapshotSource = "tmdb"
+	calendarTrendingSnapshotWindow = "week"
+)
+
 // CalendarHandler handles the calendar endpoint.
 type CalendarHandler struct {
 	repo      calendarRepository
@@ -179,23 +186,18 @@ func (h *CalendarHandler) resolveCalendarRestriction(ctx context.Context, filter
 	switch filter {
 	case calendarFilterAll, calendarFilterEverything:
 		return false, nil, nil
-	case calendarFilterFollowing:
+	case calendarFilterFollowing, calendarFilterFavorites, calendarFilterWatchlist:
 		if h.personal == nil {
 			return true, nil, nil
 		}
-		ids, err = h.personal.ListFollowedItemIDs(ctx, af.UserID, af.ProfileID)
-		return true, ids, err
-	case calendarFilterFavorites:
-		if h.personal == nil {
-			return true, nil, nil
+		switch filter {
+		case calendarFilterFavorites:
+			ids, err = h.personal.ListFavoriteItemIDs(ctx, af.UserID, af.ProfileID)
+		case calendarFilterWatchlist:
+			ids, err = h.personal.ListWatchlistItemIDs(ctx, af.UserID, af.ProfileID)
+		default: // following
+			ids, err = h.personal.ListFollowedItemIDs(ctx, af.UserID, af.ProfileID)
 		}
-		ids, err = h.personal.ListFavoriteItemIDs(ctx, af.UserID, af.ProfileID)
-		return true, ids, err
-	case calendarFilterWatchlist:
-		if h.personal == nil {
-			return true, nil, nil
-		}
-		ids, err = h.personal.ListWatchlistItemIDs(ctx, af.UserID, af.ProfileID)
 		return true, ids, err
 	case calendarFilterPopular:
 		if h.popular == nil {
@@ -214,7 +216,7 @@ func (h *CalendarHandler) resolveCalendarRestriction(ctx context.Context, filter
 		if h.trending == nil {
 			return true, nil, nil
 		}
-		snap, ok, err := h.trending.Get(ctx, "tmdb", "week")
+		snap, ok, err := h.trending.Get(ctx, calendarTrendingSnapshotSource, calendarTrendingSnapshotWindow)
 		if err != nil {
 			return true, nil, err
 		}

web/src/pages/Calendar.tsx

@@ -16,6 +16,7 @@ import { useUserLibraries } from "@/hooks/queries/libraries";
 import WeekNavigator from "@/components/calendar/WeekNavigator";
 import DayGroup from "@/components/calendar/DayGroup";
 import { addWeeks, formatDayHeading, getWeekDays, getWeekStart } from "@/lib/calendarWeek";
+import { storage } from "@/utils/storage";
 
 type CalendarFilter = "following" | "popular" | "trending" | "everything";
 
@@ -29,13 +30,10 @@ const PRESET_OPTIONS: { value: CalendarFilter; label: string }[] = [
 ];
 
 const DEFAULT_PRESET: CalendarFilter = "following";
-const PRESET_STORAGE_KEY = "calendar:preset";
 
-// Accept the four presets plus legacy server values so old shared links keep working.
+// The selectable presets plus legacy server values so old shared links keep working.
 const KNOWN_FILTERS = new Set<string>([
-  "following",
-  "trending",
-  "everything",
+  ...PRESET_OPTIONS.map((o) => o.value),
   "all",
   "favorites",
   "watchlist",
@@ -46,16 +44,14 @@ const CALENDAR_SKELETON_DAY_ROWS = 7;
 const CALENDAR_SKELETON_ITEMS_PER_ROW = 18;
 
 function readStoredPreset(): CalendarFilter {
-  if (typeof window === "undefined") return DEFAULT_PRESET;
-  const stored = window.localStorage.getItem(PRESET_STORAGE_KEY);
+  const stored = storage.get(storage.KEYS.CALENDAR_PRESET);
   return stored && PRESET_OPTIONS.some((o) => o.value === stored)
     ? (stored as CalendarFilter)
     : DEFAULT_PRESET;
 }
 
 function writeStoredPreset(value: string) {
-  if (typeof window === "undefined") return;
-  window.localStorage.setItem(PRESET_STORAGE_KEY, value);
+  storage.set(storage.KEYS.CALENDAR_PRESET, value);
 }
 
 function parseCalendarParams(searchParams: URLSearchParams) {

web/src/utils/storage.ts

@@ -13,6 +13,7 @@ const STORAGE_KEYS = {
   UI_HIGH_CONTRAST: "silo-ui-high-contrast",
   UI_CUSTOM_THEME_VARS: "silo-custom-theme-vars",
   UI_CUSTOM_CSS: "silo-custom-css",
+  CALENDAR_PRESET: "calendar:preset",
 } as const;
 
 type StorageKey = (typeof STORAGE_KEYS)[keyof typeof STORAGE_KEYS];