fix: safe performance and crash-safety fixes

- TimeGridView: remember Instant.now() (keyed on the day) and the day-header
  DateTimeFormatter instead of rebuilding both on every recomposition/frame —
  fixes flicker in the past-event dimming and avoids repeated allocation.
- CalendarViewModel.refreshFromCache: short-circuit the non-group filter pass
  when both hiddenKeys and banishedKeys are empty, mirroring the existing
  group-mode short-circuit.
- CalendarViewModel.setCalendarHiddenSynced: wrap the server PATCH in
  runCatching and surface failures via state.error instead of silently
  dropping them (the local toggle would otherwise diverge from the server
  unnoticed).
- CalendarViewModel.afterMutation: refetch only the already-cached range
  (force-bypassing loadRange's cache check) instead of invalidateCache() +
  initialLoad(), which reloaded the entire ±cacheMonths window and froze the
  UI on every single event save.
- CalendarrRoot: replace calendarVm!! with a null-safe ?.let, falling back to
  the splash screen instead of crashing if the VM isn't ready yet.
- GroupsScreen: replace existing!!.icon!! / g.icon!! double force-unwraps
  with safe-call chains (existing?.icon?.takeIf { GroupIcons.isKey(it) }).

Deliberately out of scope: R8/minify settings, MonthView's cache window
size (MONTHS_BACK/MONTHS_AHEAD), and mergeIntoCache's merge logic (already
reviewed as correct). No debounce added to setCalendarHiddenSynced — would
need new machinery beyond this fix's scope.

app/src/main/java/com/scarriffle/calendarr/ui/CalendarrRoot.kt

@@ -54,13 +54,15 @@ fun CalendarrRoot(vm: MainViewModel = hiltViewModel()) {
                         onLoggedIn = vm::onLoggedIn,
                         onBack = vm::switchServer,
                     )
-                    AppRoute.MAIN -> CalendarScreen(
+                    AppRoute.MAIN -> calendarVm?.let { cvm ->
-                        vm = calendarVm!!,
+                        CalendarScreen(
-                        onLogout = vm::logout,
+                            vm = cvm,
-                        onSwitchServer = vm::switchServer,
+                            onLogout = vm::logout,
-                        onSettingsChanged = vm::applyLocalSettings,
+                            onSwitchServer = vm::switchServer,
-                        onSettingsSynced = vm::refreshSettings,
+                            onSettingsChanged = vm::applyLocalSettings,
-                    )
+                            onSettingsSynced = vm::refreshSettings,
+                        )
+                    } ?: SplashScreen()
                 }
             }
         }

app/src/main/java/com/scarriffle/calendarr/ui/calendar/CalendarViewModel.kt

@@ -229,10 +229,12 @@ class CalendarViewModel @Inject constructor(
     }
 
     /** Single serialized loader: avoids overlapping fetches that cause scroll jank. */
-    private suspend fun loadRange(start: Instant, end: Instant, background: Boolean) {
+    private suspend fun loadRange(start: Instant, end: Instant, background: Boolean, force: Boolean = false) {
         loadMutex.withLock {
             // Another load (e.g. the background prefetch) may have covered this range.
-            if (isCached(start, end)) return
+            // `force` bypasses this so callers can explicitly re-fetch an already-cached
+            // range (e.g. to pick up a mutation) without wiping the whole cache first.
+            if (!force && isCached(start, end)) return
             val group = _state.value.activeGroup
             val flag = if (background) "bg" else "fg"
             _state.update { if (flag == "bg") it.copy(isBackgroundCaching = true) else it.copy(isLoading = true, error = null) }
@@ -305,7 +307,8 @@ class CalendarViewModel @Inject constructor(
         } else {
             val hidden = st.hiddenKeys
             val banished = st.banishedKeys
-            allCachedEvents.filter { ev ->
+            if (hidden.isEmpty() && banished.isEmpty()) allCachedEvents
+            else allCachedEvents.filter { ev ->
                 val key = calendarKey(ev.source, ev.calendarId)
                 key !in hidden && key !in banished
             }
@@ -346,7 +349,14 @@ class CalendarViewModel @Inject constructor(
         setCalendarHidden(key, hidden)
         val id = key.substringAfter(":").toIntOrNull() ?: return
         if (source in listOf("caldav", "google", "homeassistant")) {
-            viewModelScope.launch { repository.setCalendarSidebarHidden(source, id, hidden) }
+            viewModelScope.launch {
+                runCatching { repository.setCalendarSidebarHidden(source, id, hidden) }
+                    .onFailure { e ->
+                        // The local toggle already applied; only the server write failed —
+                        // surface it so the client doesn't silently diverge from server state.
+                        _state.update { it.copy(error = e.message ?: "Fehler beim Speichern") }
+                    }
+            }
         }
     }
 
@@ -427,9 +437,23 @@ class CalendarViewModel @Inject constructor(
 
     // ---- Event mutations ----
 
+    /**
+     * Re-fetch just the already-cached range after a create/update so the edit is
+     * reflected everywhere it's currently loaded, without nuking and reloading the
+     * whole ±cacheMonths window (which caused a full-screen freeze on every save).
+     * Falls back to [initialLoad] if nothing was cached yet.
+     */
     private fun afterMutation() {
-        invalidateCache()
+        val start = cachedStart
-        initialLoad()
+        val end = cachedEnd
+        if (start == null || end == null) {
+            initialLoad()
+            return
+        }
+        viewModelScope.launch {
+            loadRange(start, end, background = false, force = true)
+            markReady()
+        }
     }
 
     fun saveEvent(

app/src/main/java/com/scarriffle/calendarr/ui/calendar/TimeGridView.kt

@@ -18,6 +18,7 @@ import androidx.compose.material3.Divider
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.remember
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.draw.alpha
@@ -47,16 +48,21 @@ fun TimeGridView(
 ) {
     val hourHeight = LocalAppSettings.current.hourHeight.coerceIn(28, 100).dp
     val dimPast = LocalAppSettings.current.dimPastEvents
-    val now = java.time.Instant.now()
-    val lang = LocalLang.current
     val today = LocalDate.now()
+    // Recomputed once per day (not on every recomposition/frame) — Instant.now()
+    // was previously called fresh each recomposition, causing visible flicker in
+    // the "is this now" past-dimming and wasted allocation.
+    val now = remember(today) { java.time.Instant.now() }
+    val lang = LocalLang.current
 
     Column(Modifier.fillMaxSize()) {
         // Day headers (only for multi-day / week view)
         if (days.size > 1) {
             Row(Modifier.fillMaxWidth()) {
                 Box(Modifier.width(GUTTER))
-                val dayFmt = DateTimeFormatter.ofPattern("EEE d", com.scarriffle.calendarr.ui.L10n.locale(lang))
+                val dayFmt = remember(lang) {
+                    DateTimeFormatter.ofPattern("EEE d", com.scarriffle.calendarr.ui.L10n.locale(lang))
+                }
                 days.forEach { day ->
                     Text(
                         dayFmt.format(day),

app/src/main/java/com/scarriffle/calendarr/ui/groups/GroupsScreen.kt

@@ -208,7 +208,7 @@ private fun GroupEditSheet(
 ) {
     val me = vm.currentUserId
     var name by remember { mutableStateOf(existing?.name ?: "") }
-    var icon by remember { mutableStateOf(if (GroupIcons.isKey(existing?.icon)) existing!!.icon!! else "people") }
+    var icon by remember { mutableStateOf(existing?.icon?.takeIf { GroupIcons.isKey(it) } ?: "people") }
     var selected by remember { mutableStateOf(setOf<Int>()) }
     var existingMembers by remember { mutableStateOf(setOf<Int>()) }
     var detail by remember { mutableStateOf<Group?>(null) }
@@ -223,7 +223,7 @@ private fun GroupEditSheet(
         detail = g
         if (g != null) {
             name = g.name
-            icon = if (GroupIcons.isKey(g.icon)) g.icon!! else "people"
+            icon = g.icon?.takeIf { GroupIcons.isKey(it) } ?: "people"
             val members = g.members.map { it.id }.filter { it != me }.toSet()
             existingMembers = members
             selected = members