fix: surface per-calendar sync errors from server

/api/caldav/events now returns an "errors" array alongside "events" for
calendars that failed to sync (e.g. expired credentials) while still
reporting success overall. Previously such failures were silently
swallowed, so a calendar could appear enabled/visible while showing zero
events with no explanation.

- CalendarRepository.fetchEvents now returns EventsResult(events, errors),
  parsing the new "errors" array the same way importIcs's Triple return
  handles multi-value results.
- CalendarUiState gains syncErrors, populated in loadRange's onSuccess.
- CalendarScreen shows a second error-style banner for sync errors,
  additive to the existing network-failure banner.
- CalendarFilterSheet shows a warning icon next to calendar rows whose
  source+name matches a sync error (best-effort suffix match, since the
  server's error name is "<account> – <calendar name>").

app/src/main/java/com/scarriffle/calendarr/data/CalendarRepository.kt

@@ -35,6 +35,12 @@ data class LoginResult(val token: String, val username: String, val isAdmin: Boo
 
 data class TotpSetup(val secret: String, val qrUrl: String)
 
+/** A single calendar's sync failure, surfaced alongside a (still-successful) events fetch. */
+data class SyncError(val source: String, val name: String, val message: String)
+
+/** Result of [CalendarRepository.fetchEvents]: the merged events plus any per-calendar sync failures. */
+data class EventsResult(val events: List<CalEvent>, val errors: List<SyncError>)
+
 /**
  * Single entry point for all server interaction. Wraps [com.scarriffle.calendarr.data.remote.CalendarrApi],
  * converts HTTP failures into [ApiException]s carrying the server's `detail`
@@ -297,18 +303,30 @@ class CalendarRepository @Inject constructor(
 
     // ---- Events ----
 
-    suspend fun fetchEvents(start: Instant, end: Instant): List<CalEvent> = withContext(Dispatchers.IO) {
+    suspend fun fetchEvents(start: Instant, end: Instant): EventsResult = withContext(Dispatchers.IO) {
         val resp = api.fetchEvents(Dates.isoUtc(start), Dates.isoUtc(end))
         resp.ensureSuccess()
-        val raw = resp.body()?.string() ?: return@withContext emptyList()
+        val raw = resp.body()?.string() ?: return@withContext EventsResult(emptyList(), emptyList())
         val root = JSONObject(raw)
-        val arr = root.optJSONArray("events") ?: return@withContext emptyList()
-        buildList {
-            for (i in 0 until arr.length()) {
+        val arr = root.optJSONArray("events")
+        val events = buildList {
+            if (arr != null) for (i in 0 until arr.length()) {
                 val obj = arr.optJSONObject(i) ?: continue
                 CalEvent.fromJson(obj)?.let { add(it) }
             }
         }
+        val errArr = root.optJSONArray("errors")
+        val errors = buildList {
+            if (errArr != null) for (i in 0 until errArr.length()) {
+                val obj = errArr.optJSONObject(i) ?: continue
+                add(SyncError(
+                    source = obj.optString("source"),
+                    name = obj.optString("name"),
+                    message = obj.optString("message"),
+                ))
+            }
+        }
+        EventsResult(events, errors)
     }
 
     suspend fun createLocalEvent(

app/src/main/java/com/scarriffle/calendarr/ui/L10n.kt

@@ -122,6 +122,7 @@ object L10n {
             "filter.title" to "Kalender", "filter.empty" to "Keine Kalender vorhanden",
             "filter.show_all" to "Alle anzeigen", "filter.hide_all" to "Alle ausblenden",
             "filter.button" to "Kalender ein-/ausblenden",
+            "filter.sync_error" to "Synchronisierung fehlgeschlagen",
             "caldav.display_name" to "Anzeigename", "caldav.url" to "CalDAV-URL",
             "caldav.username" to "Benutzername", "caldav.password" to "Passwort",
             "caldav.color" to "Farbe", "caldav.connect" to "Verbinden", "caldav.title" to "CalDAV-Konto",
@@ -260,6 +261,7 @@ object L10n {
             "filter.title" to "Calendars", "filter.empty" to "No calendars available",
             "filter.show_all" to "Show all", "filter.hide_all" to "Hide all",
             "filter.button" to "Show/hide calendars",
+            "filter.sync_error" to "Sync failed",
             "caldav.display_name" to "Display name", "caldav.url" to "CalDAV URL",
             "caldav.username" to "Username", "caldav.password" to "Password",
             "caldav.color" to "Color", "caldav.connect" to "Connect", "caldav.title" to "CalDAV account",

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

@@ -12,6 +12,7 @@ import androidx.compose.foundation.shape.CircleShape
 import androidx.compose.material.icons.Icons
 import androidx.compose.material.icons.filled.Notifications
 import androidx.compose.material.icons.filled.NotificationsOff
+import androidx.compose.material.icons.filled.WarningAmber
 import androidx.compose.material3.ExperimentalMaterial3Api
 import androidx.compose.material3.Icon
 import androidx.compose.material3.IconButton
@@ -83,11 +84,24 @@ fun CalendarFilterSheet(
             }
             rows.forEach { entry ->
                 val visible = entry.key !in hiddenSet
+                // Best-effort match: server error `name` is "<account> – <calendar name>",
+                // so a suffix match on this calendar's own name is reliable enough.
+                val hasSyncError = !groupMode && state.syncErrors.any { err ->
+                    err.source == entry.source && err.name.endsWith(entry.name)
+                }
                 Row(
                     Modifier.fillMaxWidth().padding(vertical = 8.dp),
                     verticalAlignment = Alignment.CenterVertically,
                 ) {
                     Box(Modifier.size(14.dp).clip(CircleShape).background(colorFromHex(entry.color)))
+                    if (hasSyncError) {
+                        Icon(
+                            Icons.Filled.WarningAmber,
+                            contentDescription = tr("filter.sync_error"),
+                            tint = MaterialTheme.colorScheme.error,
+                            modifier = Modifier.padding(start = 8.dp).size(16.dp),
+                        )
+                    }
                     Text(
                         entry.name,
                         modifier = Modifier.weight(1f).padding(start = 12.dp),

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

@@ -172,6 +172,9 @@ fun CalendarScreen(
             state.error?.let { err ->
                 ErrorBanner(err, onRetry = { vm.loadVisible(force = true) }, onDismiss = vm::clearError)
             }
+            if (state.syncErrors.isNotEmpty()) {
+                SyncErrorBanner(state.syncErrors, onDismiss = vm::clearSyncErrors)
+            }
             state.activeGroup?.let { g ->
                 GroupBanner(group = g, onExit = { vm.switchGroup(null) })
             }
@@ -344,6 +347,33 @@ private fun ErrorBanner(message: String, onRetry: () -> Unit, onDismiss: () -> U
     }
 }
 
+/**
+ * Additive to [ErrorBanner]: the fetch as a whole succeeded, but one or more
+ * enabled calendars failed to sync (e.g. expired credentials) and are showing
+ * zero events with no other indication. Same visual language, no retry button
+ * (retrying the whole range wouldn't target just the broken calendar).
+ */
+@Composable
+private fun SyncErrorBanner(errors: List<com.scarriffle.calendarr.data.SyncError>, onDismiss: () -> Unit) {
+    androidx.compose.material3.Surface(
+        color = MaterialTheme.colorScheme.errorContainer,
+        modifier = Modifier.fillMaxWidth(),
+    ) {
+        Column(Modifier.padding(12.dp)) {
+            errors.forEach { err ->
+                Text(
+                    "${err.name}: ${err.message}",
+                    color = MaterialTheme.colorScheme.onErrorContainer,
+                    style = MaterialTheme.typography.bodySmall,
+                )
+            }
+            androidx.compose.foundation.layout.Row {
+                TextButton(onClick = onDismiss) { Text(tr("common.close")) }
+            }
+        }
+    }
+}
+
 @Composable
 private fun loadingPlaceholder() {
     Box(Modifier.fillMaxSize(), contentAlignment = Alignment.Center) {

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

@@ -4,6 +4,7 @@ import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import com.scarriffle.calendarr.data.CalendarRepository
 import com.scarriffle.calendarr.data.SettingsStore
+import com.scarriffle.calendarr.data.SyncError
 import com.scarriffle.calendarr.domain.model.CalEvent
 import com.scarriffle.calendarr.domain.model.CalViewType
 import com.scarriffle.calendarr.domain.model.Group
@@ -36,6 +37,10 @@ data class CalendarUiState(
     val isLoading: Boolean = false,
     val isBackgroundCaching: Boolean = false,
     val error: String? = null,
+    // Per-calendar sync failures from the last successful /events fetch (e.g.
+    // expired CalDAV credentials) — the fetch as a whole succeeded, but one or
+    // more enabled calendars silently returned nothing. Additive to `error`.
+    val syncErrors: List<SyncError> = emptyList(),
     val weekStartsOnMonday: Boolean = true,
     val writableCalendars: List<WritableCalendar> = emptyList(),
     val hiddenKeys: Set<String> = emptySet(),
@@ -232,10 +237,14 @@ class CalendarViewModel @Inject constructor(
             val flag = if (background) "bg" else "fg"
             _state.update { if (flag == "bg") it.copy(isBackgroundCaching = true) else it.copy(isLoading = true, error = null) }
             runCatching {
-                if (group != null) decorateGroup(repository.fetchGroupCombined(group.id, start, end))
-                else repository.fetchEvents(start, end)
+                if (group != null) decorateGroup(repository.fetchGroupCombined(group.id, start, end)) to emptyList<SyncError>()
+                else repository.fetchEvents(start, end).let { it.events to it.errors }
             }
-                .onSuccess { mergeIntoCache(it, start, end); refreshFromCache() }
+                .onSuccess { (events, errors) ->
+                    mergeIntoCache(events, start, end)
+                    refreshFromCache()
+                    _state.update { it.copy(syncErrors = errors) }
+                }
                 .onFailure { e -> if (!background) _state.update { it.copy(error = e.message) } }
             _state.update { it.copy(isLoading = false, isBackgroundCaching = false) }
         }
@@ -319,6 +328,8 @@ class CalendarViewModel @Inject constructor(
 
     fun clearError() = _state.update { it.copy(error = null) }
 
+    fun clearSyncErrors() = _state.update { it.copy(syncErrors = emptyList()) }
+
     // ---- Visibility filters ----
 
     fun setCalendarHidden(key: String, hidden: Boolean) {