deleteSlot method

Future<void> deleteSlot(String id)

Deletes slot id: removes its metadata AND every key namespaced to it via keyFor (through StorageService.removeAllWithPrefix) — no leftover keys from a deleted slot. If id was the activeSlotId, that becomes null afterward (never left pointing at a slot that no longer exists). Throws ArgumentError if id doesn't exist.

Implementation

Future<void> deleteSlot(String id) async {
  _validateExists(id);
  final storage = StorageService.to;
  // BUG-87: data delete FIRST — if THIS throws, metadata/activeSlotId are
  // untouched below, so a failed delete never orphans a slot's data (no
  // metadata pointing at it, but the data itself still on disk). The old
  // order removed metadata first, so a mid-delete crash/throw left data
  // on disk with no metadata entry (and possibly activeSlotId still
  // pointing at a slot that no longer "exists" per listSlots()).
  final dataSnapshot = storage.exportWithPrefix('slot_${id}_');
  await storage.removeAllWithPrefix('slot_${id}_');

  // Snapshot in-memory metadata state BEFORE mutating it, so a failure to
  // actually PERSIST the removal (verified below, not merely "didn't
  // throw" — a swallowed error inside `_scheduleSave`'s fire-and-forget
  // save chain would otherwise silently leave stale metadata on disk
  // while this method returns as if fully committed) can roll everything
  // — data, in-memory metadata, and the active-slot pointer — back to
  // exactly the pre-delete state instead of leaving a partial delete
  // behind.
  final metaSnapshot = List<SaveSlotMeta>.of(_slotList);
  final wasActive = activeSlotId == id;
  _slotList.removeWhere((s) => s.id == id);
  _scheduleSave();
  await _waitForPendingSaves();

  final persistedIds = (_store.load() ?? const <SaveSlotMeta>[])
      .map((s) => s.id)
      .toSet();
  if (persistedIds.contains(id)) {
    // Metadata removal never actually reached disk (the save chain's own
    // `catch (_) {}` swallowed a real write failure) — restore data,
    // in-memory metadata, and rollback the failed removal attempt with
    // one more (best-effort) save, then surface the failure instead of
    // returning as if the slot were gone.
    if (dataSnapshot.isNotEmpty) {
      await storage.importWithPrefix('slot_${id}_', dataSnapshot);
    }
    _slots = metaSnapshot;
    _scheduleSave();
    await _waitForPendingSaves();
    throw StateError(
      'deleteSlot: metadata removal for "$id" failed to persist; rolled '
      'back',
    );
  }

  if (wasActive) {
    await storage.remove(_activeSlotStorageKey);
  }
}