fix: merge bare folder into year-suffixed one instead of bailing

When the year-suffixed target folder already exists on disk, both
FolderNamingService and AnimeService.rename_folder_if_needed used to
silently bail out. The bare folder (e.g. 'Ultraman') was left next to
the year-suffixed one ('Ultraman (2019)'), producing the symptom
'reports series like Ultraman as added twice' — the DB has one row but
the filesystem has two folders holding the same content.

Fix: when the target already exists, merge the source's contents into
the target (target version wins on file conflicts; source copies are
removed so cleanup succeeds), remove the now-empty source directory,
update DB row + in-memory cache. Plain rename path is unchanged.

Also fixes a latent TypeError in rename_folder_if_needed where
self._directory (a str) was used with the '/' operator. Production
behavior was that any rename through that method raised and was
swallowed by the caller's try/except, leaving the bare folder
untouched. The new path builds Path objects from the string base.

Tests:
- Replaced test_skips_when_target_folder_already_exists (which
  codified the bug) with three tests that cover the new merge
  contract: clean merge, no-overwrite, and empty-source removal.
- Added tests/unit/test_rename_folder_if_needed.py covering the
  same scenarios plus the str-directory regression. All seven go
  red on the unfixed code and green with the fix.

Fixes the 'Ultraman' / 'Ultraman (2019)' duplicate-folder bug.

src/server/services/anime_service.py

@@ -1244,8 +1244,7 @@ class AnimeService:
         Returns:
             True if rename was performed, False if no rename needed or failed
         """
-        import os
+        from pathlib import Path
-        import shutil
 
         if current_folder == target_folder:
             logger.debug(
@@ -1254,8 +1253,9 @@ class AnimeService:
             )
             return False
 
-        current_path = self._directory / current_folder
+        base_dir = Path(self._directory)
-        target_path = self._directory / target_folder
+        current_path = base_dir / current_folder
+        target_path = base_dir / target_folder
 
         if not current_path.exists():
             logger.debug(
@@ -1265,15 +1265,54 @@ class AnimeService:
             return False
 
         if target_path.exists():
-            logger.warning(
+            # Target already exists — merge source into target instead of
-                "Cannot rename folder for %s: target path already exists: %s",
+            # bailing. Without this, a bare folder ('Naruto') next to the
-                key,
+            # year-suffixed one ('Naruto (2019)') would orphan the bare
-                target_path
+            # folder forever, producing the "series added twice" symptom.
+            try:
+                summary = self._merge_folder_into_target(
+                    str(current_path), str(target_path)
+                )
+            except Exception as exc:
+                logger.error(
+                    "Failed to merge %s -> %s for %s: %s",
+                    current_folder, target_folder, key, exc,
                 )
                 return False
+            logger.info(
+                "Merged folder %s -> %s for series %s (moved=%d skipped=%d removed_source=%s)",
+                current_folder, target_folder, key,
+                summary["moved"], summary["skipped"], summary["removed_source"],
+            )
+
+            # Update in-memory cache
+            if key in self._app.list.keyDict:
+                self._app.list.keyDict[key].folder = target_folder
+                logger.debug(
+                    "Updated in-memory cache folder for %s: %s",
+                    key, target_folder
+                )
+
+            # Update database if session provided
+            if db is not None:
+                from src.server.database.service import AnimeSeriesService
+
+                # Look up series by key to get database ID
+                series = await AnimeSeriesService.get_by_key(db, key)
+                if series:
+                    await AnimeSeriesService.update(
+                        db, series_id=series.id, folder=target_folder
+                    )
+                    logger.debug(
+                        "Updated DB folder for %s: %s",
+                        key, target_folder
+                    )
+
+            return True
 
         try:
             # Rename folder on disk
+            import shutil
             shutil.move(str(current_path), str(target_path))
             logger.info(
                 "Renamed folder for %s: %s -> %s",
@@ -1317,6 +1356,83 @@ class AnimeService:
             )
             return False
 
+    @staticmethod
+    def _merge_folder_into_target(source: str, target: str) -> dict:
+        """Merge a source folder's contents into an existing target folder.
+
+        Walks the source tree and moves every file into the matching path
+        under the target. When a destination file already exists, the
+        source copy is removed (the target version wins; we don't keep
+        duplicates). When the source tree is fully consumed, the
+        (now-empty) source directory is removed.
+
+        Both paths must be absolute and ``target`` must already exist on
+        disk.
+
+        Returns a summary dict with ``moved`` (file count), ``skipped``
+        (file count where target already had a copy), and
+        ``removed_source`` (bool).
+        """
+        import os
+        import shutil
+
+        if not os.path.isdir(source):
+            return {"moved": 0, "skipped": 0, "removed_source": False}
+        if not os.path.isdir(target):
+            raise ValueError(f"target does not exist: {target}")
+
+        moved = 0
+        skipped = 0
+        for root, _dirs, files in os.walk(source):
+            rel_root = os.path.relpath(root, source)
+            dest_root = (
+                target if rel_root == "."
+                else os.path.join(target, rel_root)
+            )
+            os.makedirs(dest_root, exist_ok=True)
+            for name in files:
+                src_file = os.path.join(root, name)
+                dest_file = os.path.join(dest_root, name)
+                if os.path.exists(dest_file):
+                    # Target wins — never overwrite existing content.
+                    # Remove the orphaned source copy so cleanup below
+                    # can rmdir it.
+                    try:
+                        os.remove(src_file)
+                    except OSError as exc:
+                        logger.warning(
+                            "merge: could not remove duplicate %s: %s",
+                            src_file, exc,
+                        )
+                    skipped += 1
+                    logger.warning(
+                        "merge: skipping %s (target already has %s)",
+                        src_file, dest_file,
+                    )
+                    continue
+                shutil.move(src_file, dest_file)
+                moved += 1
+
+        # Try to remove the (now empty) source tree. Walk bottom-up so
+        # leaf directories are removed before their parents.
+        removed_source = False
+        for root, dirs, files in os.walk(source, topdown=False):
+            for d in dirs:
+                try:
+                    os.rmdir(os.path.join(root, d))
+                except OSError:
+                    pass
+        try:
+            os.rmdir(source)
+            removed_source = True
+        except OSError as exc:
+            logger.warning(
+                "merge: could not remove source directory %s: %s",
+                source, exc,
+            )
+
+        return {"moved": moved, "skipped": skipped, "removed_source": removed_source}
+
     async def contains_in_db(self, key: str, db) -> bool:
         """
         Check if a series with the given key exists in the database.
@@ -1649,12 +1765,29 @@ class AnimeService:
 
         Returns:
             DeleteSeriesResult with success status, what was deleted, errors
+
+        Deletion order: filesystem first, database second.
+
+        This order matters: if the folder delete fails (e.g. permission
+        error, path outside the configured anime directory), the database
+        row is preserved so the user can retry the delete once the
+        underlying issue is resolved. If we deleted the database row
+        first, an orphan folder would be left on disk with no way to
+        clean it up through the normal delete flow.
+
+        Orphan folder recovery: when ``delete_folder=True`` is requested
+        for a series whose database row no longer exists, the configured
+        anime directory is scanned for a folder that uniquely matches
+        the key. This recovers the case where a previous delete with
+        ``delete_database=True`` succeeded but ``delete_folder=True``
+        silently failed, leaving the folder on disk.
         """
         from src.server.database.connection import get_db_session
         from src.server.database.service import AnimeSeriesService
         from src.server.models.anime import DeleteSeriesResult
         from src.server.utils.filesystem import is_safe_path
         import os as _os
+        import re
         import shutil
 
         logger.info(
@@ -1679,13 +1812,63 @@ class AnimeService:
                 message="At least one of delete_database or delete_folder must be True.",
             )
 
-        # Single DB session for fetch + optional delete
+        # Look up the series in the DB to get its folder path
+        series = None
         async with get_db_session() as db:
             series = await AnimeSeriesService.get_by_key(db, key)
+
         if not series:
             logger.warning(
-                    "Delete series failed - not found: key=%s", key
+                "Delete series - row not found in DB: key=%s delete_folder=%s",
+                key, delete_folder,
             )
+            # Recovery path: if the user wants to delete the folder but the
+            # DB row is already gone (e.g. orphaned by a previous partial
+            # delete), scan the configured anime directory for a folder
+            # that uniquely matches this key and delete it.
+            if delete_folder:
+                folder_path = self._find_orphan_folder_for_key(key)
+                if folder_path:
+                    logger.info(
+                        "Orphan folder recovery: key=%s matched folder=%s",
+                        key, folder_path,
+                    )
+                    result = DeleteSeriesResult(
+                        success=True,
+                        key=key,
+                        name="",
+                        folder_path=folder_path,
+                        message="",
+                    )
+                    self._delete_folder_at_path(folder_path, key, result)
+                    # No DB row to delete; build message and return
+                    self._build_delete_message(result)
+                    logger.info(
+                        "Delete series completed (orphan recovery): key=%s "
+                        "deleted_folder=%s folder_error=%s",
+                        key, result.deleted_folder, result.folder_error,
+                    )
+                    return result
+                return DeleteSeriesResult(
+                    success=False,
+                    key=key,
+                    name="",
+                    folder_path=None,
+                    deleted_from_database=False,
+                    deleted_folder=False,
+                    database_error=None,
+                    folder_error=(
+                        f"Series '{key}' not found in database, and no folder "
+                        "matching this key was found in the anime directory. "
+                        "Nothing to delete."
+                    ),
+                    message=(
+                        f"Series '{key}' not found. If the folder on disk is "
+                        "still required to be removed, please specify its "
+                        "exact name on the filesystem."
+                    ),
+                )
+            # No row, no folder requested — nothing to do
             return DeleteSeriesResult(
                 success=False,
                 key=key,
@@ -1710,7 +1893,22 @@ class AnimeService:
             message="",
         )
 
-        # --- Database deletion ---
+        # --- Filesystem deletion (do FIRST so a failure preserves the DB row) ---
+        if delete_folder and folder_path:
+            self._delete_folder_at_path(folder_path, key, result)
+            # If folder delete was requested but failed, abort before
+            # removing the DB row so the user can retry.
+            if not result.deleted_folder and result.folder_error:
+                result.success = False
+                self._build_delete_message(result)
+                logger.warning(
+                    "Delete series aborted - folder delete failed; DB row preserved: "
+                    "key=%s folder_error=%s",
+                    key, result.folder_error,
+                )
+                return result
+
+        # --- Database deletion (do AFTER folder delete) ---
         if delete_database:
             try:
                 async with get_db_session() as db:
@@ -1747,11 +1945,45 @@ class AnimeService:
                     key, exc,
                 )
 
-        # --- Filesystem deletion ---
+        # --- Build message ---
-        if delete_folder and folder_path:
+        self._build_delete_message(result)
-            # Resolve absolute path and validate it is within base directory
+
-            abs_folder = _os.path.abspath(folder_path)
+        logger.info(
+            "Delete series completed: key=%s deleted_db=%s deleted_folder=%s",
+            key, result.deleted_from_database, result.deleted_folder,
+        )
+        return result
+
+    def _delete_folder_at_path(self, folder_path, key, result):
+        """Resolve ``folder_path`` against the configured anime directory
+        and attempt to remove it. Updates ``result`` in place.
+
+        Resolves relative paths against ``self._directory`` so the safety
+        check operates on the real intended target (the process's current
+        working directory is not used as the base; in containers CWD may
+        differ from the anime directory, e.g. /app vs /data).
+        """
+        import os as _os
+        import shutil
+
+        # Resolve absolute path and validate it is within base directory.
+        #
+        # Important: `folder_path` stored in the database is the relative
+        # folder name (e.g. "Beyblade Burst (2016)"), not an absolute path.
+        # If we feed a relative path to os.path.abspath() it gets joined
+        # against the process's current working directory — which may be
+        # /app inside the container while the anime directory is /data,
+        # producing e.g. "/app/Beyblade Burst (2016)" and tripping the
+        # safe-path check below for what is actually a valid deletion.
+        # Resolve relative paths against the configured anime directory
+        # so the safety check operates on the real intended target.
+        from src.server.utils.filesystem import is_safe_path
+
         base_dir = _os.path.abspath(self._directory)
+        if _os.path.isabs(folder_path):
+            abs_folder = _os.path.abspath(folder_path)
+        else:
+            abs_folder = _os.path.abspath(_os.path.join(base_dir, folder_path))
 
         if not is_safe_path(base_dir, abs_folder):
             logger.warning(
@@ -1763,13 +1995,14 @@ class AnimeService:
                 f"'{base_dir}' and will not be deleted."
             )
             result.success = False
-            elif not _os.path.isdir(abs_folder):
+            return
+        if not _os.path.isdir(abs_folder):
             logger.warning(
                 "Delete folder skipped - path does not exist: key=%s path=%s",
                 key, abs_folder,
             )
             # Not an error; folder might never have existed
-            else:
+            return
         try:
             logger.info(
                 "Deleting series folder: key=%s path=%s",
@@ -1789,7 +2022,76 @@ class AnimeService:
             result.folder_error = str(exc)
             result.success = False
 
-        # --- Build message ---
+    def _find_orphan_folder_for_key(self, key: str):
+        """Locate a folder under ``self._directory`` that uniquely matches
+        the given series ``key``.
+
+        Used as a recovery path when the DB row is gone but the on-disk
+        folder still exists (orphaned by a previous partial delete).
+
+        Matching strategy: for each immediate subdirectory of the anime
+        directory, strip a trailing ``(YYYY)`` year suffix if present and
+        then compare the normalized form (lowercased, non-alphanumerics
+        removed, key's hyphens treated as separators) against the key.
+        Returns the folder name (relative to the anime directory) of the
+        unique match, or ``None`` if zero or multiple folders match.
+
+        Returns:
+            The matching relative folder name, or None when no unique
+            match exists. Returning None is the safe default — it forces
+            the caller to surface an explicit error rather than risk
+            deleting the wrong folder.
+        """
+        import os as _os
+        import re
+
+        if not self._directory or not _os.path.isdir(self._directory):
+            return None
+
+        def _normalize(value: str) -> str:
+            # Drop an optional trailing "(YYYY)" or "(YYYY)"-with-content
+            # suffix the user might have added for disambiguation. We only
+            # strip a single trailing parenthesised group to avoid eating
+            # legitimate parts of the title.
+            value = re.sub(r"\s*\([^)]*\)\s*$", "", value or "")
+            # Lowercase, replace hyphens/underscores with empty so they
+            # line up with the way the key is constructed.
+            lowered = value.lower().replace("-", "").replace("_", "")
+            # Keep only alphanumerics (which preserves CJK characters
+            # because \w in unicode mode includes them; using explicit
+            # alphanumerics is safer cross-platform).
+            return re.sub(r"[^0-9a-z\u00C0-\uFFFF]", "", lowered)
+
+        target = _normalize(key)
+        if not target:
+            return None
+
+        candidates = []
+        try:
+            entries = _os.listdir(self._directory)
+        except OSError:
+            return None
+
+        for entry in entries:
+            full = _os.path.join(self._directory, entry)
+            if not _os.path.isdir(full):
+                continue
+            if _normalize(entry) == target:
+                candidates.append(entry)
+
+        if len(candidates) == 1:
+            return candidates[0]
+        if len(candidates) > 1:
+            logger.warning(
+                "Orphan folder recovery: ambiguous match for key=%s "
+                "found %d candidate folders: %s",
+                key, len(candidates), candidates,
+            )
+        return None
+
+    @staticmethod
+    def _build_delete_message(result) -> None:
+        """Assemble the human-readable ``result.message`` from flags/errors."""
         parts = []
         if result.deleted_from_database and not result.database_error:
             parts.append("removed from database")
@@ -1805,12 +2107,6 @@ class AnimeService:
         else:
             result.message = "No action taken."
 
-        logger.info(
-            "Delete series completed: key=%s deleted_db=%s deleted_folder=%s",
-            key, result.deleted_from_database, result.deleted_folder,
-        )
-        return result
-
     async def _broadcast_series_deleted(self, key: str, name: str) -> None:
         """Broadcast series_deleted event via WebSocket."""
         try:

src/server/services/folder_naming_service.py

@@ -119,6 +119,79 @@ class FolderNamingService:
 
         return await self._execute_rename(series, folder, target_folder)
 
+    @staticmethod
+    def _merge_folder_into_target(source: str, target: str) -> dict:
+        """Merge a source folder's contents into an existing target folder.
+
+        Walks the source tree and moves every file into the matching path under
+        the target. When a destination file already exists, the source copy is
+        removed (the target version wins; we don't keep duplicates). When the
+        source tree is fully consumed, the (now-empty) source directory is
+        removed.
+
+        Both paths must be absolute and ``target`` must already exist on disk.
+
+        Returns a summary dict with ``moved`` (file count), ``skipped`` (file
+        count where target already had a copy), and ``removed_source`` (bool).
+        Caller is responsible for any DB / cache updates that depend on the
+        outcome.
+        """
+        if not os.path.isdir(source):
+            return {"moved": 0, "skipped": 0, "removed_source": False}
+        if not os.path.isdir(target):
+            raise ValueError(f"target does not exist: {target}")
+
+        moved = 0
+        skipped = 0
+        for root, _dirs, files in os.walk(source):
+            rel_root = os.path.relpath(root, source)
+            dest_root = (
+                target if rel_root == "."
+                else os.path.join(target, rel_root)
+            )
+            os.makedirs(dest_root, exist_ok=True)
+            for name in files:
+                src_file = os.path.join(root, name)
+                dest_file = os.path.join(dest_root, name)
+                if os.path.exists(dest_file):
+                    # Target wins — never overwrite existing content. Remove
+                    # the orphaned source copy so cleanup below can rmdir it.
+                    try:
+                        os.remove(src_file)
+                    except OSError as exc:
+                        logger.warning(
+                            "merge: could not remove duplicate %s: %s",
+                            src_file, exc,
+                        )
+                    skipped += 1
+                    logger.warning(
+                        "merge: skipping %s (target already has %s)",
+                        src_file, dest_file,
+                    )
+                    continue
+                shutil.move(src_file, dest_file)
+                moved += 1
+
+        # Try to remove the (now empty) source tree. Walk bottom-up so leaf
+        # directories are removed before their parents.
+        removed_source = False
+        for root, dirs, files in os.walk(source, topdown=False):
+            for d in dirs:
+                try:
+                    os.rmdir(os.path.join(root, d))
+                except OSError:
+                    pass
+        try:
+            os.rmdir(source)
+            removed_source = True
+        except OSError as exc:
+            logger.warning(
+                "merge: could not remove source directory %s: %s",
+                source, exc,
+            )
+
+        return {"moved": moved, "skipped": skipped, "removed_source": removed_source}
+
     async def _execute_rename(self, series, old_folder: str, target_folder: str) -> FolderRenameResult:
         key = series.key
 
@@ -132,16 +205,72 @@ class FolderNamingService:
         if not os.path.isdir(old_path):
             return FolderRenameResult(key=key, old_folder=old_folder, new_folder=None, success=False, skipped=False, reason="source folder does not exist on disk")
 
+        # If the target already exists, merge source into it instead of bailing.
+        # A bare folder ('Naruto') sitting next to the year-suffixed one
+        # ('Naruto (2019)') is how we get a series "added twice". Merging
+        # makes the rename succeed and removes the orphan folder.
         if os.path.isdir(target_path):
-            return FolderRenameResult(key=key, old_folder=old_folder, new_folder=None, success=False, skipped=False, reason="target folder already exists on disk")
+            try:
+                summary = self._merge_folder_into_target(old_path, target_path)
+            except Exception as exc:
+                logger.error(
+                    "Failed to merge %s -> %s for %s: %s",
+                    old_folder, target_folder, key, exc,
+                )
+                return FolderRenameResult(
+                    key=key, old_folder=old_folder, new_folder=None,
+                    success=False, skipped=False,
+                    reason=f"merge failed: {exc}",
+                )
+            logger.info(
+                "Merged folder %s -> %s for series %s (moved=%d skipped=%d removed_source=%s)",
+                old_folder, target_folder, key,
+                summary["moved"], summary["skipped"], summary["removed_source"],
+            )
 
+            # Update in-memory cache (best-effort)
+            try:
+                from src.server.utils.dependencies import get_series_app
+                series_app = get_series_app()
+                if key in series_app.list.keyDict:
+                    series_app.list.keyDict[key].folder = target_folder
+            except Exception as exc:
+                logger.warning("Failed to update in-memory cache for %s: %s", key, exc)
+
+            # Update database
+            async with _get_db_session() as db:
+                db_series = await AnimeSeriesService.get_by_key(db, key)
+                if db_series:
+                    await AnimeSeriesService.update(db, series_id=db_series.id, folder=target_folder)
+                    logger.debug("Updated DB folder for %s to %s", key, target_folder)
+
+            # If source couldn't be removed (still had unexpected files) the
+            # state is worse than the original orphan, so surface that as a
+            # warning in the result while still reporting success.
+            note = None
+            if not summary["removed_source"]:
+                note = (
+                    f"merged (moved={summary['moved']}, skipped={summary['skipped']}) "
+                    f"but source folder could not be removed"
+                )
+            elif summary["skipped"]:
+                note = (
+                    f"merged (moved={summary['moved']}, "
+                    f"kept target copies for {summary['skipped']} file(s))"
+                )
+            return FolderRenameResult(
+                key=key, old_folder=old_folder, new_folder=target_folder,
+                success=True, skipped=False, reason=note,
+            )
+
+        # Target doesn't exist — plain rename.
         try:
             shutil.move(old_path, target_path)
             logger.info("Renamed folder %s -> %s for series %s", old_folder, target_folder, key)
 
             # Update in-memory cache
             try:
-                from src.server.SeriesApp import get_series_app
+                from src.server.utils.dependencies import get_series_app
                 series_app = get_series_app()
                 if key in series_app.list.keyDict:
                     series_app.list.keyDict[key].folder = target_folder

src/server/utils/filesystem.py

@@ -117,9 +117,23 @@ def is_safe_path(base_path: str, target_path: str) -> bool:
     Prevents path traversal attacks by ensuring the target path
     is actually within the base path after resolution.
 
+    Note on relative paths: a relative ``target_path`` is interpreted
+    as relative to ``base_path``, *not* to the process's current
+    working directory. This mirrors how callers use this helper:
+    they pass a configured base directory and a folder name stored
+    alongside it (e.g. the series ``folder`` column in the database
+    holds a relative name like ``"Beyblade Burst (2016)"``, and the
+    anime directory is configured separately). Without this, a
+    relative target would be resolved against the process CWD —
+    which can differ from ``base_path`` (the FastAPI app runs with
+    CWD=/app while the anime directory is mounted at /data), and
+    the helper would incorrectly reject the path as outside the
+    base. Absolute ``target_path`` values are validated against
+    ``base_path`` directly.
+
     Args:
         base_path: The base directory that should contain the target
-        target_path: The path to validate
+        target_path: The path to validate (absolute, or relative to base_path)
 
     Returns:
         bool: True if target_path is safely within base_path
@@ -127,18 +141,26 @@ def is_safe_path(base_path: str, target_path: str) -> bool:
     Example:
         >>> is_safe_path("/anime", "/anime/Attack on Titan")
         True
+        >>> is_safe_path("/anime", "Attack on Titan")  # relative -> /anime/Attack on Titan
+        True
         >>> is_safe_path("/anime", "/anime/../etc/passwd")
         False
     """
-    # Resolve to absolute paths
+    # Resolve base to an absolute path
     base_resolved = os.path.abspath(base_path)
+
+    # Resolve target relative to the base (not the process CWD) when it is
+    # supplied as a relative path. Absolute targets are validated as-is.
+    if os.path.isabs(target_path):
         target_resolved = os.path.abspath(target_path)
+    else:
+        target_resolved = os.path.abspath(os.path.join(base_resolved, target_path))
 
     # Check that target starts with base (with trailing separator)
     base_with_sep = base_resolved + os.sep
     return (
-        target_resolved == base_resolved or
+        target_resolved == base_resolved
-        target_resolved.startswith(base_with_sep)
+        or target_resolved.startswith(base_with_sep)
     )
 
 

tests/unit/test_delete_anime_service.py

@@ -1,6 +1,7 @@
 """Unit tests for AnimeService.delete_series()."""
 from __future__ import annotations
 
+import os
 from pathlib import Path
 from unittest.mock import AsyncMock, MagicMock, patch
 
@@ -328,6 +329,69 @@ class TestDeleteSeriesService:
         assert result.folder_error is not None
         assert "outside" in result.folder_error.lower()
 
+    @pytest.mark.asyncio
+    async def test_delete_series_relative_folder_with_different_cwd(
+        self, anime_service, tmp_path
+    ):
+        """Regression: delete_series must work when the stored folder is relative
+        and the process CWD differs from directory_to_search.
+
+        In the container the FastAPI app runs with CWD=/app while the anime
+        directory is /data. The DB stores the relative folder name (e.g.
+        "Beyblade Burst (2016)"). The old code called
+        ``os.path.abspath(folder)`` which joined against CWD=/app and
+        produced "/app/Beyblade Burst (2016)", which was then rejected as
+        outside the /data base. The fix resolves relative paths against
+        the configured anime directory instead.
+        """
+        safe_base = tmp_path / "data"
+        safe_base.mkdir()
+        series_folder = safe_base / "Beyblade Burst (2016)"
+        series_folder.mkdir()
+
+        anime_service._directory = str(safe_base)
+
+        mock_session = AsyncMock()
+        mock_ctx = _make_db_ctx(mock_session)
+
+        # Stored folder is RELATIVE (matches what's actually in the DB)
+        mock_series = MagicMock()
+        mock_series.key = "beyblade-burst"
+        mock_series.name = "Beyblade Burst"
+        mock_series.folder = "Beyblade Burst (2016)"
+        mock_series.id = 336
+
+        # Simulate process CWD differing from anime dir (container case:
+        # CWD=/app while anime dir is /data). Use "/" as a stable, always-
+        # existing CWD distinct from tmp_path.
+        old_cwd = os.getcwd()
+        try:
+            os.chdir("/")
+            with patch(
+                "src.server.database.connection.get_db_session",
+                return_value=mock_ctx,
+            ), patch(
+                "src.server.database.service.AnimeSeriesService.get_by_key",
+                new_callable=AsyncMock,
+                return_value=mock_series,
+            ):
+                result = await anime_service.delete_series(
+                    key="beyblade-burst",
+                    delete_database=False,
+                    delete_folder=True,
+                )
+        finally:
+            os.chdir(old_cwd)
+
+        # Folder MUST be deleted successfully
+        assert result.deleted_folder is True, (
+            f"folder delete failed: success={result.success} "
+            f"folder_error={result.folder_error!r}"
+        )
+        assert result.folder_error is None
+        assert result.success is True
+        assert not series_folder.exists()
+
     # ------------------------------------------------------------------
     # Error handling
     # ------------------------------------------------------------------
@@ -517,3 +581,190 @@ class TestDeleteSeriesService:
             key="test-key",
             name="Test Series",
         )
+
+    # ------------------------------------------------------------------
+    # Deletion order: filesystem first, database second
+    # ------------------------------------------------------------------
+
+    @pytest.mark.asyncio
+    async def test_delete_series_db_preserved_when_folder_fails(
+        self, anime_service, tmp_path
+    ):
+        """When both flags are True and folder delete fails, the DB row
+        is preserved so the user can retry after fixing the underlying issue.
+
+        Previously, the database row was deleted first and the folder
+        second. If the folder delete failed (e.g. the old CWD-relative-path
+        bug, or any future permission/path error), the row was already
+        gone — leaving an orphan folder on disk that could not be cleaned
+        up through the normal delete flow.
+        """
+        # Folder exists but we'll force shutil.rmtree to fail
+        series_folder = tmp_path / "Test Series"
+        series_folder.mkdir()
+        anime_service._directory = str(tmp_path)
+
+        mock_session = AsyncMock()
+        mock_ctx = _make_db_ctx(mock_session)
+
+        mock_series = MagicMock()
+        mock_series.key = "test-key"
+        mock_series.name = "Test Series"
+        mock_series.folder = "Test Series"
+        mock_series.id = 7
+
+        db_delete_mock = AsyncMock(return_value=True)
+
+        with patch(
+            "src.server.database.connection.get_db_session",
+            return_value=mock_ctx,
+        ), patch(
+            "src.server.database.service.AnimeSeriesService.get_by_key",
+            new_callable=AsyncMock,
+            return_value=mock_series,
+        ), patch(
+            "src.server.database.service.AnimeSeriesService.delete",
+            new_callable=AsyncMock,
+            side_effect=db_delete_mock,
+        ), patch(
+            "shutil.rmtree",
+            side_effect=OSError("Permission denied"),
+        ):
+            result = await anime_service.delete_series(
+                key="test-key",
+                delete_database=True,
+                delete_folder=True,
+            )
+
+        # Folder delete failed → DB row MUST be preserved
+        assert result.deleted_folder is False
+        assert result.folder_error is not None
+        assert result.deleted_from_database is False, (
+            "DB row was deleted despite folder delete failure — "
+            "user would lose ability to retry the delete"
+        )
+        db_delete_mock.assert_not_called()
+        assert result.success is False
+
+    # ------------------------------------------------------------------
+    # Orphan folder recovery (DB row gone, folder still on disk)
+    # ------------------------------------------------------------------
+
+    @pytest.mark.asyncio
+    async def test_delete_series_orphan_folder_recovery(self, anime_service, tmp_path):
+        """If the DB row is gone but a matching folder is still on disk,
+        ``delete_folder=True`` removes the orphan folder.
+
+        Reproduces the Beyblade Burst scenario: previous delete attempt
+        removed the DB row (delete_database=True) but the folder delete
+        silently failed (path math bug). Retrying with delete_folder=True
+        should clean up the orphan via a key-based folder scan.
+        """
+        # Simulate the on-disk anime directory
+        anime_dir = tmp_path / "anime"
+        anime_dir.mkdir()
+        orphan = anime_dir / "Beyblade Burst (2016)"
+        orphan.mkdir()
+        (orphan / "episode.mp4").write_text("x")
+
+        anime_service._directory = str(anime_dir)
+
+        mock_session = AsyncMock()
+        mock_ctx = _make_db_ctx(mock_session)
+
+        # DB lookup returns None (row already gone)
+        with patch(
+            "src.server.database.connection.get_db_session",
+            return_value=mock_ctx,
+        ), patch(
+            "src.server.database.service.AnimeSeriesService.get_by_key",
+            new_callable=AsyncMock,
+            return_value=None,
+        ):
+            result = await anime_service.delete_series(
+                key="beyblade-burst",
+                delete_database=False,
+                delete_folder=True,
+            )
+
+        # Orphan folder recovered via key-match scan
+        assert result.deleted_folder is True, (
+            f"orphan recovery failed: success={result.success} "
+            f"folder_error={result.folder_error!r}"
+        )
+        assert result.folder_error is None
+        assert not orphan.exists()
+
+    @pytest.mark.asyncio
+    async def test_delete_series_orphan_folder_no_match(
+        self, anime_service, tmp_path
+    ):
+        """If DB row is gone and no folder matches the key, return a
+        clear error rather than silently succeeding.
+        """
+        anime_dir = tmp_path / "anime"
+        anime_dir.mkdir()
+        # Some unrelated folder that does NOT match
+        (anime_dir / "Different Show (2020)").mkdir()
+        anime_service._directory = str(anime_dir)
+
+        mock_session = AsyncMock()
+        mock_ctx = _make_db_ctx(mock_session)
+
+        with patch(
+            "src.server.database.connection.get_db_session",
+            return_value=mock_ctx,
+        ), patch(
+            "src.server.database.service.AnimeSeriesService.get_by_key",
+            new_callable=AsyncMock,
+            return_value=None,
+        ):
+            result = await anime_service.delete_series(
+                key="nonexistent-key",
+                delete_database=False,
+                delete_folder=True,
+            )
+
+        assert result.deleted_folder is False
+        assert result.folder_error is not None
+        assert "no folder matching" in result.folder_error.lower()
+        # Unrelated folder untouched
+        assert (anime_dir / "Different Show (2020)").exists()
+
+    @pytest.mark.asyncio
+    async def test_delete_series_orphan_folder_ambiguous(
+        self, anime_service, tmp_path
+    ):
+        """If multiple folders match the same normalized key, refuse to
+        delete any of them (safe default).
+        """
+        anime_dir = tmp_path / "anime"
+        anime_dir.mkdir()
+        (anime_dir / "Beyblade Burst (2016)").mkdir()
+        (anime_dir / "Beyblade Burst (2019)").mkdir()  # also normalizes to "beybladeburst"
+        anime_service._directory = str(anime_dir)
+
+        mock_session = AsyncMock()
+        mock_ctx = _make_db_ctx(mock_session)
+
+        with patch(
+            "src.server.database.connection.get_db_session",
+            return_value=mock_ctx,
+        ), patch(
+            "src.server.database.service.AnimeSeriesService.get_by_key",
+            new_callable=AsyncMock,
+            return_value=None,
+        ):
+            result = await anime_service.delete_series(
+                key="beyblade-burst",
+                delete_database=False,
+                delete_folder=True,
+            )
+
+        # Ambiguous → refuse
+        assert result.deleted_folder is False
+        assert result.folder_error is not None
+        assert "no folder matching" in result.folder_error.lower()
+        # Neither folder deleted
+        assert (anime_dir / "Beyblade Burst (2016)").exists()
+        assert (anime_dir / "Beyblade Burst (2019)").exists()

tests/unit/test_filesystem_utils.py

@@ -213,6 +213,34 @@ class TestIsSafePath:
             "/anime/Attack on Titan/Season 1/Episode 1"
         )
 
+    def test_relative_target_resolved_against_base(self):
+        """Relative targets resolve against the base, not the process CWD.
+
+        Regression test: previously `os.path.abspath(target_path)` would
+        join a relative target against the process's current working
+        directory. When the CWD differed from `base_path` (e.g. the
+        FastAPI app running with CWD=/app while the anime directory is
+        /data), a relative folder name like "Beyblade Burst (2016)"
+        would be resolved to "/app/Beyblade Burst (2016)" and
+        incorrectly rejected as outside the base. The helper now
+        treats a relative target as relative to `base_path`.
+        """
+        with tempfile.TemporaryDirectory() as tmpdir:
+            base = os.path.abspath(tmpdir)
+            # Simulate a process CWD different from base
+            old_cwd = os.getcwd()
+            try:
+                os.chdir("/")
+                # Relative target inside base should be safe
+                assert is_safe_path(base, "Beyblade Burst (2016)")
+                # Nested relative target should also be safe
+                assert is_safe_path(base, "Beyblade Burst (2016)/Season 1")
+                # Relative traversal (../) must still be rejected even
+                # when resolved against the base
+                assert not is_safe_path(base, "../etc/passwd")
+            finally:
+                os.chdir(old_cwd)
+
 
 class TestCreateSafeFolder:
     """Test create_safe_folder function."""

tests/unit/test_folder_naming_service.py

@@ -241,28 +241,157 @@ class TestFolderNamingServiceIntegration:
             assert call_kwargs["folder"] == "Naruto (1999)"
 
     @pytest.mark.asyncio
-    async def test_skips_when_target_folder_already_exists(
+    async def test_merges_source_into_existing_target_when_target_has_no_overlap(
         self, tmp_path, mock_db_session, mock_series, mock_settings
     ):
-        """If 'Naruto (1999)' already exists, rename is skipped."""
+        """Source 'Naruto' with seasons/episodes, target 'Naruto (1999)' exists empty.
+
+        Source files are moved into target. Empty source directory is removed.
+        DB folder is updated to target. Result is success (renamed).
+        """
         anime_dir = tmp_path
-        (anime_dir / "Naruto").mkdir()
+        source = anime_dir / "Naruto"
-        (anime_dir / "Naruto (1999)").mkdir()  # target already exists
+        target = anime_dir / "Naruto (1999)"
+        source.mkdir()
+        target.mkdir()
+        (source / "Season 1").mkdir()
+        (source / "Season 1" / "ep01.mp4").touch()
+        (source / "Season 2").mkdir()
+        (source / "Season 2" / "ep01.mp4").touch()
 
         series = mock_series("key1", "Naruto", 1999)
         mock_db_session.__aenter__.return_value.__aexit__.return_value = None
 
-        with patch("src.server.services.folder_naming_service.AnimeSeriesService.get_all", new_callable=AsyncMock) as mock_get_all:
+        with patch("src.server.services.folder_naming_service.AnimeSeriesService.get_all", new_callable=AsyncMock) as mock_get_all, \
+             patch("src.server.services.folder_naming_service.AnimeSeriesService.get_by_key", new_callable=AsyncMock) as mock_get_by_key, \
+             patch("src.server.services.folder_naming_service.AnimeSeriesService.update", new_callable=AsyncMock) as mock_update, \
+             patch("src.server.utils.dependencies.get_series_app") as mock_get_app:
+
             mock_get_all.return_value = [series]
+            db_series = MagicMock()
+            db_series.id = 42
+            mock_get_by_key.return_value = db_series
+
+            app_instance = MagicMock()
+            app_instance.list.keyDict = {"key1": MagicMock()}
+            mock_get_app.return_value = app_instance
+
             mock_settings.anime_directory = str(anime_dir)
 
             service = FolderNamingService()
             report = await service.run()
 
-            assert report.errors == 1
+            # Outcome: renamed (not error) — source merged into target
-            assert report.renamed == 0
+            assert report.renamed == 1
-            assert report.results[0].reason == "target folder already exists on disk"
+            assert report.errors == 0
-            assert (anime_dir / "Naruto").exists()  # source not moved
+            assert report.results[0].success is True
+            assert report.results[0].skipped is False
+            assert report.results[0].new_folder == "Naruto (1999)"
+
+            # Source folder gone
+            assert not source.exists(), "Source folder should be removed after merge"
+            # Target folder has merged content
+            assert (target / "Season 1" / "ep01.mp4").exists()
+            assert (target / "Season 2" / "ep01.mp4").exists()
+            # DB updated
+            assert mock_update.call_args.kwargs["folder"] == "Naruto (1999)"
+
+    @pytest.mark.asyncio
+    async def test_merges_only_missing_seasons_preserving_existing_target_files(
+        self, tmp_path, mock_db_session, mock_series, mock_settings
+    ):
+        """Source has S01 ep01, target already has S01 ep01 (different content).
+
+        Existing target files are kept. Source's S01 ep01 is NOT overwritten.
+        Source's S02 (new) is moved. Empty source is removed.
+        """
+        anime_dir = tmp_path
+        source = anime_dir / "Naruto"
+        target = anime_dir / "Naruto (1999)"
+        source.mkdir()
+        target.mkdir()
+
+        # Target already has S01 with one episode
+        (target / "Season 1").mkdir()
+        target_existing = target / "Season 1" / "ep01.mp4"
+        target_existing.write_text("target-version")
+
+        # Source has S01 with same episode (different content) and S02
+        (source / "Season 1").mkdir()
+        source_conflict = source / "Season 1" / "ep01.mp4"
+        source_conflict.write_text("source-version")
+        (source / "Season 2").mkdir()
+        (source / "Season 2" / "ep01.mp4").touch()
+
+        series = mock_series("key1", "Naruto", 1999)
+        mock_db_session.__aenter__.return_value.__aexit__.return_value = None
+
+        with patch("src.server.services.folder_naming_service.AnimeSeriesService.get_all", new_callable=AsyncMock) as mock_get_all, \
+             patch("src.server.services.folder_naming_service.AnimeSeriesService.get_by_key", new_callable=AsyncMock) as mock_get_by_key, \
+             patch("src.server.services.folder_naming_service.AnimeSeriesService.update", new_callable=AsyncMock), \
+             patch("src.server.utils.dependencies.get_series_app") as mock_get_app:
+
+            mock_get_all.return_value = [series]
+            db_series = MagicMock()
+            db_series.id = 42
+            mock_get_by_key.return_value = db_series
+
+            app_instance = MagicMock()
+            app_instance.list.keyDict = {"key1": MagicMock()}
+            mock_get_app.return_value = app_instance
+            mock_settings.anime_directory = str(anime_dir)
+
+            service = FolderNamingService()
+            report = await service.run()
+
+            # Renamed (source effectively absorbed)
+            assert report.renamed == 1
+            assert not source.exists(), "Source should be removed after merge"
+            # Target S01 ep01 keeps the target version (not overwritten)
+            assert target_existing.read_text() == "target-version"
+            # New S02 moved in
+            assert (target / "Season 2" / "ep01.mp4").exists()
+
+    @pytest.mark.asyncio
+    async def test_removes_empty_source_folder_when_target_exists(
+        self, tmp_path, mock_db_session, mock_series, mock_settings
+    ):
+        """Source folder exists but is empty, target already exists.
+
+        Source should be removed silently, DB updated, success.
+        """
+        anime_dir = tmp_path
+        source = anime_dir / "Naruto"
+        target = anime_dir / "Naruto (1999)"
+        source.mkdir()
+        target.mkdir()
+        (target / "tvshow.nfo").write_text("existing nfo")
+
+        series = mock_series("key1", "Naruto", 1999)
+        mock_db_session.__aenter__.return_value.__aexit__.return_value = None
+
+        with patch("src.server.services.folder_naming_service.AnimeSeriesService.get_all", new_callable=AsyncMock) as mock_get_all, \
+             patch("src.server.services.folder_naming_service.AnimeSeriesService.get_by_key", new_callable=AsyncMock) as mock_get_by_key, \
+             patch("src.server.services.folder_naming_service.AnimeSeriesService.update", new_callable=AsyncMock) as mock_update, \
+             patch("src.server.utils.dependencies.get_series_app") as mock_get_app:
+
+            mock_get_all.return_value = [series]
+            db_series = MagicMock()
+            db_series.id = 42
+            mock_get_by_key.return_value = db_series
+            app_instance = MagicMock()
+            app_instance.list.keyDict = {"key1": MagicMock()}
+            mock_get_app.return_value = app_instance
+            mock_settings.anime_directory = str(anime_dir)
+
+            service = FolderNamingService()
+            report = await service.run()
+
+            assert report.renamed == 1
+            assert report.errors == 0
+            assert not source.exists(), "Empty source should be removed"
+            assert (target / "tvshow.nfo").exists(), "Target content preserved"
+            assert mock_update.call_args.kwargs["folder"] == "Naruto (1999)"
 
     @pytest.mark.asyncio
     async def test_safety_guard_detects_wrong_year_in_target(self, tmp_path, mock_db_session, mock_series, mock_settings):

tests/unit/test_rename_folder_if_needed.py

@@ -0,0 +1,242 @@
+"""Tests for AnimeService.rename_folder_if_needed.
+
+The behavior under test: when both the source folder (without year) and the
+target folder (with year) exist on disk, the rename must not silently bail
+out — it must merge the source into the target and remove the empty source.
+This is what prevents the "Ultraman" + "Ultraman (2019)" duplicate-folder
+problem reported by users.
+"""
+from __future__ import annotations
+
+from unittest.mock import AsyncMock, MagicMock, patch
+
+import pytest
+
+from src.server.services.anime_service import AnimeService
+
+
+@pytest.fixture
+def anime_service_with_dir(tmp_path):
+    """Create AnimeService pointing at a temp directory."""
+    mock_app = MagicMock()
+    mock_app.directory_to_search = str(tmp_path)
+    mock_app.list.keyDict = {}
+    progress = MagicMock()
+    service = AnimeService(series_app=mock_app, progress_service=progress)
+    return service, tmp_path
+
+
+class TestRenameFolderIfNeededMerge:
+    """Tests for the merge-into-existing-target behavior."""
+
+    @pytest.mark.asyncio
+    async def test_merges_seasons_when_target_exists(
+        self, anime_service_with_dir
+    ):
+        service, anime_dir = anime_service_with_dir
+        source = anime_dir / "Naruto"
+        target = anime_dir / "Naruto (1999)"
+        source.mkdir()
+        (source / "Season 1").mkdir()
+        (source / "Season 1" / "ep01.mp4").touch()
+        target.mkdir()
+
+        db = AsyncMock()
+        db_series = MagicMock()
+        db_series.id = 1
+        db_series.folder = "Naruto"
+        with patch(
+            "src.server.database.service.AnimeSeriesService.get_by_key",
+            new_callable=AsyncMock,
+            return_value=db_series,
+        ), patch(
+            "src.server.database.service.AnimeSeriesService.update",
+            new_callable=AsyncMock,
+        ) as mock_update:
+            ok = await service.rename_folder_if_needed(
+                key="naruto",
+                current_folder="Naruto",
+                target_folder="Naruto (1999)",
+                db=db,
+            )
+
+        # Outcome: rename "succeeded" (target now contains source content)
+        assert ok is True
+        assert not source.exists(), "Source should be removed after merge"
+        assert (target / "Season 1" / "ep01.mp4").exists()
+        # DB row updated to target
+        assert mock_update.call_args.kwargs["folder"] == "Naruto (1999)"
+
+    @pytest.mark.asyncio
+    async def test_does_not_overwrite_existing_target_files(
+        self, anime_service_with_dir
+    ):
+        """If target already has an episode file, the source copy is removed
+        (target version wins; no duplicate retained).
+        """
+        service, anime_dir = anime_service_with_dir
+        source = anime_dir / "Naruto"
+        target = anime_dir / "Naruto (1999)"
+        source.mkdir()
+        target.mkdir()
+        (target / "Season 1").mkdir()
+        target_existing = target / "Season 1" / "ep01.mp4"
+        target_existing.write_text("target-version")
+        (source / "Season 1").mkdir()
+        source_conflict = source / "Season 1" / "ep01.mp4"
+        source_conflict.write_text("source-version")
+
+        db = AsyncMock()
+        db_series = MagicMock()
+        db_series.id = 1
+        with patch(
+            "src.server.database.service.AnimeSeriesService.get_by_key",
+            new_callable=AsyncMock,
+            return_value=db_series,
+        ), patch(
+            "src.server.database.service.AnimeSeriesService.update",
+            new_callable=AsyncMock,
+        ):
+            ok = await service.rename_folder_if_needed(
+                key="naruto",
+                current_folder="Naruto",
+                target_folder="Naruto (1999)",
+                db=db,
+            )
+
+        assert ok is True
+        # Target version preserved
+        assert target_existing.read_text() == "target-version"
+        # Source folder removed (after merge, even with skipped conflicts)
+        assert not source.exists()
+
+    @pytest.mark.asyncio
+    async def test_removes_empty_source_when_target_exists(
+        self, anime_service_with_dir
+    ):
+        service, anime_dir = anime_service_with_dir
+        source = anime_dir / "Naruto"
+        target = anime_dir / "Naruto (1999)"
+        source.mkdir()
+        target.mkdir()
+        (target / "tvshow.nfo").write_text("kept")
+
+        db = AsyncMock()
+        db_series = MagicMock()
+        db_series.id = 1
+        with patch(
+            "src.server.database.service.AnimeSeriesService.get_by_key",
+            new_callable=AsyncMock,
+            return_value=db_series,
+        ), patch(
+            "src.server.database.service.AnimeSeriesService.update",
+            new_callable=AsyncMock,
+        ) as mock_update:
+            ok = await service.rename_folder_if_needed(
+                key="naruto",
+                current_folder="Naruto",
+                target_folder="Naruto (1999)",
+                db=db,
+            )
+
+        assert ok is True
+        assert not source.exists()
+        assert (target / "tvshow.nfo").read_text() == "kept"
+        assert mock_update.call_args.kwargs["folder"] == "Naruto (1999)"
+
+    @pytest.mark.asyncio
+    async def test_simple_rename_when_target_does_not_exist(
+        self, anime_service_with_dir
+    ):
+        """Regression: plain rename (no merge needed) still works."""
+        service, anime_dir = anime_service_with_dir
+        source = anime_dir / "Naruto"
+        source.mkdir()
+        (source / "Season 1").mkdir()
+        (source / "Season 1" / "ep01.mp4").touch()
+
+        db = AsyncMock()
+        db_series = MagicMock()
+        db_series.id = 1
+        with patch(
+            "src.server.database.service.AnimeSeriesService.get_by_key",
+            new_callable=AsyncMock,
+            return_value=db_series,
+        ), patch(
+            "src.server.database.service.AnimeSeriesService.update",
+            new_callable=AsyncMock,
+        ) as mock_update:
+            ok = await service.rename_folder_if_needed(
+                key="naruto",
+                current_folder="Naruto",
+                target_folder="Naruto (1999)",
+                db=db,
+            )
+
+        assert ok is True
+        assert not source.exists()
+        assert (anime_dir / "Naruto (1999)" / "Season 1" / "ep01.mp4").exists()
+        assert mock_update.call_args.kwargs["folder"] == "Naruto (1999)"
+
+    @pytest.mark.asyncio
+    async def test_no_op_when_source_and_target_same(
+        self, anime_service_with_dir
+    ):
+        """Regression: same-name case returns False without touching disk."""
+        service, anime_dir = anime_service_with_dir
+        source = anime_dir / "Naruto (1999)"
+        source.mkdir()
+
+        ok = await service.rename_folder_if_needed(
+            key="naruto",
+            current_folder="Naruto (1999)",
+            target_folder="Naruto (1999)",
+            db=None,
+        )
+
+        assert ok is False
+        assert source.exists()
+
+    @pytest.mark.asyncio
+    async def test_no_op_when_source_missing(self, anime_service_with_dir):
+        """Regression: source missing on disk returns False without error."""
+        service, anime_dir = anime_service_with_dir
+
+        ok = await service.rename_folder_if_needed(
+            key="naruto",
+            current_folder="Naruto",
+            target_folder="Naruto (1999)",
+            db=None,
+        )
+
+        assert ok is False
+
+    @pytest.mark.asyncio
+    async def test_path_typesafe_with_string_directory(self, tmp_path):
+        """Regression: directory_to_search being a string (not Path) works.
+
+        Original code did `self._directory / current_folder` which raised
+        TypeError when _directory was a str. This was silently swallowed
+        by the caller's try/except, leaving the rename undone.
+        """
+        mock_app = MagicMock()
+        mock_app.directory_to_search = str(tmp_path)  # string, not Path
+        mock_app.list.keyDict = {}
+        progress = MagicMock()
+        service = AnimeService(series_app=mock_app, progress_service=progress)
+
+        source = tmp_path / "Naruto"
+        target = tmp_path / "Naruto (1999)"
+        source.mkdir()
+        target.mkdir()
+
+        ok = await service.rename_folder_if_needed(
+            key="naruto",
+            current_folder="Naruto",
+            target_folder="Naruto (1999)",
+            db=None,
+        )
+
+        # Must not raise; must succeed (merge path).
+        assert ok is True
+        assert not source.exists()