fix(nas): refuse deletes while library storage is unreachable; real file removal; stat cache

Three changes from the network-drive audit:

1. Delete-ordering fix. Deleting a media item cascades its annotations,
   so the delete must never proceed while the item's library storage is
   unreachable — the DB row died, the file survived as an orphan, and
   the next scan re-imported it bare (annotations gone forever).
   resolveMediaStorage stats the library's folders: reachable → delete
   proceeds and the file is removed by ABSOLUTE path (the old code
   passed a library-relative path to os.Remove, which never resolved —
   file deletion has been a silent no-op); every folder unreachable →
   409 with 'storage unreachable', row and annotations intact.

2. Latency: resolveLibrary stats every library folder on every SSR
   render; folder reachability is now cached with a 30s TTL.

3. README: Network Storage section documenting the outage hysteresis
   (mark → archive → auto-restore), the 90-day retention purge
   (ARCHIVE_RETENTION_DAYS, 0 = never), refused deletes while storage
   is down, and watch mode not firing on network mounts.

Integration tests: storage-down bulk delete refuses with the row
intact; real-file delete removes the file from disk.

internal/handlers/media.go

@@ -439,6 +439,20 @@ func (h *MediaHandler) HandleBulkDelete(c *echo.Context) error {
 			continue
 		}
 
+		// Storage-down guard: deleting cascades the item's annotations, so
+		// refuse while the library storage is unreachable — the file would
+		// survive as an orphan and re-import bare on the next scan.
+		storage := h.resolveMediaStorage(c.Request().Context(), uuid.UUID(media.LibraryID.Bytes).String(), media.FilePath)
+		if !storage.Reachable {
+			results = append(results, map[string]interface{}{
+				"media_item_id": mediaIDStr,
+				"status":        "error",
+				"error":         "storage unreachable — archive the item instead, or retry when the storage is mounted",
+			})
+			failedCount++
+			continue
+		}
+
 		err = h.db.DeleteMediaItem(c.Request().Context(), mediaUUID)
 		if err != nil {
 			results = append(results, map[string]interface{}{
@@ -450,11 +464,11 @@ func (h *MediaHandler) HandleBulkDelete(c *echo.Context) error {
 			continue
 		}
 
-		if media.FilePath != "" {
-			if err := os.Remove(media.FilePath); err != nil {
+		if storage.AbsolutePath != "" {
+			if err := os.Remove(storage.AbsolutePath); err != nil {
 				// Log file removal failure but don't fail the request
 				// DB record is already deleted, which is the primary concern
-				log.Printf("Warning: failed to remove file %s: %v", media.FilePath, err)
+				log.Printf("Warning: failed to remove file %s: %v", storage.AbsolutePath, err)
 			}
 		}
 
@@ -649,6 +663,54 @@ func (mh *MediaHandler) visibleLibrarySet(c *echo.Context) (map[string]bool, []p
 	return set, ids, nil
 }
 
+// mediaStorageState reports whether the library storage holding a media
+// item's file is currently reachable, and resolves the file's absolute
+// path when it can be located.
+//
+// Why this exists: deleting a media item cascades its annotations, so the
+// delete must never proceed while the storage is unreachable — otherwise
+// a NAS outage turns an admin cleanup into permanent annotation loss
+// (the DB row dies, the orphaned file re-imports bare on the next scan).
+type mediaStorageState struct {
+	// Absolute path of the file when located on reachable storage;
+	// empty when the file is missing or reachability is undeterminable.
+	AbsolutePath string
+	// Reachable is false ONLY when the library has folders and every one
+	// of them fails to stat — positive evidence the mount is down. When
+	// no folders are configured reachability is undeterminable and this
+	// is true (delete proceeds; behavior unchanged from before this check).
+	Reachable bool
+}
+
+func (mh *MediaHandler) resolveMediaStorage(ctx context.Context, libraryID string, relativePath string) mediaStorageState {
+	libUUID, err := uuid.Parse(libraryID)
+	if err != nil {
+		return mediaStorageState{Reachable: true}
+	}
+	folders, err := mh.libraryService.GetLibraryFolders(ctx, pgtype.UUID{Bytes: libUUID, Valid: true})
+	if err != nil || len(folders) == 0 {
+		return mediaStorageState{Reachable: true}
+	}
+
+	anyFolderUp := false
+	for _, f := range folders {
+		if _, err := os.Stat(f.FolderPath); err != nil {
+			continue // folder root unreachable
+		}
+		anyFolderUp = true
+		candidate := filepath.Join(f.FolderPath, filepath.FromSlash(relativePath))
+		if _, err := os.Stat(candidate); err == nil {
+			return mediaStorageState{AbsolutePath: candidate, Reachable: true}
+		}
+	}
+	if !anyFolderUp {
+		return mediaStorageState{Reachable: false}
+	}
+	// Storage is up but the file is genuinely gone: a stale row is safe
+	// to delete.
+	return mediaStorageState{Reachable: true}
+}
+
 // ListMediaItems handles GET /api/media-items
 func (mh *MediaHandler) ListMediaItems(c *echo.Context) error {
 	libraryID := c.QueryParam("library_id")
@@ -1599,11 +1661,35 @@ func (mh *MediaHandler) DeleteMediaItem(c *echo.Context) error {
 		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid media item id"})
 	}
 
+	media, err := mh.db.GetMediaItem(c.Request().Context(), pgtype.UUID{Bytes: mediaUUID, Valid: true})
+	if err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return c.JSON(http.StatusNotFound, map[string]string{"error": "media item not found"})
+		}
+		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
+	}
+
+	// Storage-down guard (see HandleBulkDelete): refuse while the library
+	// storage is unreachable so the cascade can't destroy annotations for
+	// a file that will re-import on the next scan.
+	storage := mh.resolveMediaStorage(c.Request().Context(), uuid.UUID(media.LibraryID.Bytes).String(), media.FilePath)
+	if !storage.Reachable {
+		return c.JSON(http.StatusConflict, map[string]string{
+			"error": "storage unreachable — archive the item instead, or retry when the storage is mounted",
+		})
+	}
+
 	err = mh.db.DeleteMediaItem(c.Request().Context(), pgtype.UUID{Bytes: mediaUUID, Valid: true})
 	if err != nil {
 		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
 	}
 
+	if storage.AbsolutePath != "" {
+		if err := os.Remove(storage.AbsolutePath); err != nil {
+			log.Printf("Warning: failed to remove file %s: %v", storage.AbsolutePath, err)
+		}
+	}
+
 	return c.NoContent(http.StatusNoContent)
 }