refactor: route sidecar/preview path derivation through sidecar_paths helpers

Phase 1 of #1045 (optional centralized sidecar storage): introduce
py/utils/sidecar_paths.py as the single place that resolves .metadata.json
and preview locations, and replace all inline splitext-based derivations
across scanners, services, download manager, and route handlers.

No behavior change: the default 'alongside' storage mode resolves every
path exactly as before. .civitai.info (third-party sidecar) derivation is
intentionally left co-located.

py/metadata_ops/__init__.py

@@ -172,12 +172,13 @@ async def download_preview(
     """
     from ..services.downloader import get_downloader
     from ..utils.exif_utils import ExifUtils
+    from ..utils.sidecar_paths import get_preview_dir
 
     if not url or not url.strip():
         return None
 
     base_name = os.path.splitext(os.path.basename(model_path))[0]
-    preview_dir = os.path.dirname(model_path)
+    preview_dir = get_preview_dir(model_path)
     output_path = os.path.join(preview_dir, base_name + ".webp")
 
     downloader = await get_downloader()

py/routes/handlers/misc_handlers.py

@@ -68,6 +68,7 @@ from ...utils.example_images_paths import (
 )
 from ...utils.lora_metadata import extract_trained_words
 from ...utils.session_logging import get_standalone_session_log_snapshot
+from ...utils.sidecar_paths import get_metadata_path, get_preview_dir
 from ...utils.usage_stats import UsageStats
 from .base_model_handlers import BaseModelHandlerSet
 
@@ -943,15 +944,24 @@ class DoctorHandler:
 
                             os.rename(path, new_path)
 
-                            for suffix in (".metadata.json", ".civitai.info"):
-                                old_sidecar = old_base_no_ext + suffix
-                                new_sidecar = new_base_no_ext + suffix
-                                if os.path.exists(old_sidecar):
-                                    os.rename(old_sidecar, new_sidecar)
+                            old_metadata_path = get_metadata_path(path)
+                            new_metadata_path = get_metadata_path(new_path)
+                            if os.path.exists(old_metadata_path):
+                                os.rename(old_metadata_path, new_metadata_path)
+
+                            old_sidecar = old_base_no_ext + ".civitai.info"
+                            new_sidecar = new_base_no_ext + ".civitai.info"
+                            if os.path.exists(old_sidecar):
+                                os.rename(old_sidecar, new_sidecar)
 
                             for preview_ext in PREVIEW_EXTENSIONS:
-                                old_preview = old_base_no_ext + preview_ext
-                                new_preview = new_base_no_ext + preview_ext
+                                old_preview = os.path.join(
+                                    get_preview_dir(path), base_name + preview_ext
+                                )
+                                new_preview = os.path.join(
+                                    get_preview_dir(new_path),
+                                    candidate_base + preview_ext,
+                                )
                                 if os.path.exists(old_preview):
                                     os.rename(old_preview, new_preview)
 
@@ -963,7 +973,10 @@ class DoctorHandler:
                                     old_preview_url = entry["preview_url"].replace("\\", "/")
                                     preview_ext = os.path.splitext(old_preview_url)[1]
                                     if preview_ext:
-                                        entry["preview_url"] = (new_base_no_ext + preview_ext).replace(os.sep, "/")
+                                        entry["preview_url"] = os.path.join(
+                                            get_preview_dir(new_path),
+                                            candidate_base + preview_ext,
+                                        ).replace(os.sep, "/")
                                 await scanner.update_single_model_cache(
                                     path, new_path, entry
                                 )

py/routes/handlers/model_handlers.py

@@ -50,6 +50,7 @@ from ...services.errors import RateLimitError, ResourceNotFoundError
 from ...utils.civitai_utils import resolve_license_payload
 from ...utils.file_utils import calculate_sha256
 from ...utils.metadata_manager import MetadataManager
+from ...utils.sidecar_paths import get_metadata_path
 from ...utils.url_utils import relative_root_prefix
 
 LICENSE_FIELDS = (
@@ -676,7 +677,7 @@ class ModelManagementHandler:
                     status=400,
                 )
 
-            metadata_path = os.path.splitext(file_path)[0] + ".metadata.json"
+            metadata_path = get_metadata_path(file_path)
             local_metadata = await self._metadata_sync.load_local_metadata(
                 metadata_path
             )

py/services/autov3_backfill_service.py

@@ -27,6 +27,8 @@ import os
 import threading
 from typing import TYPE_CHECKING, Optional
 
+from ..utils.sidecar_paths import get_metadata_path
+
 if TYPE_CHECKING:  # pragma: no cover - type-check only; runtime imports are local
     from .model_scanner import ModelScanner
 
@@ -41,7 +43,7 @@ def _resolve_autov3(file_path: str) -> str:
     safetensors header hash. Returns ``''`` when neither is available.
     """
     try:
-        metadata_path = f"{os.path.splitext(file_path)[0]}.metadata.json"
+        metadata_path = get_metadata_path(file_path)
         if os.path.exists(metadata_path):
             with open(metadata_path, "r", encoding="utf-8") as handle:
                 payload = json.load(handle)

py/services/download_manager.py

@@ -38,6 +38,7 @@ from ..utils.preview_selection import resolve_mature_threshold, select_preview_m
 from ..utils.utils import calculate_filename_for_model, sanitize_folder_name
 from ..utils.exif_utils import ExifUtils
 from ..utils.metadata_manager import MetadataManager
+from ..utils.sidecar_paths import get_metadata_path, get_preview_dir
 from .service_registry import ServiceRegistry
 from .download_routing import is_diffusion_model_download, resolve_other_download_sub_type
 from .settings_manager import get_settings_manager
@@ -831,7 +832,7 @@ class DownloadManager:
                 )
 
         for file_path in target_files:
-            metadata_path = os.path.splitext(file_path)[0] + ".metadata.json"
+            metadata_path = get_metadata_path(file_path)
             deleted = await self._delete_file_with_retries(metadata_path)
             if not deleted and os.path.exists(metadata_path):
                 logger.error(f"Error deleting metadata file: {metadata_path}")
@@ -2447,7 +2448,7 @@ class DownloadManager:
                 return {"success": False, "error": save_path}
 
             part_path = save_path + ".part"
-            metadata_path = os.path.splitext(save_path)[0] + ".metadata.json"
+            metadata_path = get_metadata_path(save_path)
 
             pause_control = self._pause_events.get(download_id) if download_id else None
 
@@ -2503,7 +2504,10 @@ class DownloadManager:
 
                     if media_type == "video":
                         preview_ext = _extension_from_url(preview_url, ".mp4")
-                        preview_path = os.path.splitext(save_path)[0] + preview_ext
+                        preview_path = os.path.join(
+                            get_preview_dir(save_path),
+                            os.path.splitext(os.path.basename(save_path))[0] + preview_ext,
+                        )
                         rewritten_url, rewritten = rewrite_preview_url(
                             preview_url, media_type="video"
                         )
@@ -2530,7 +2534,10 @@ class DownloadManager:
                         )
                         if rewritten and rewritten_url:
                             preview_ext = _extension_from_url(preview_url, ".png")
-                            preview_path = os.path.splitext(save_path)[0] + preview_ext
+                            preview_path = os.path.join(
+                                get_preview_dir(save_path),
+                                os.path.splitext(os.path.basename(save_path))[0] + preview_ext,
+                            )
                             success, _ = await downloader.download_file(
                                 rewritten_url, preview_path, use_auth=False
                             )
@@ -2557,8 +2564,9 @@ class DownloadManager:
                                         temp_file_handle.write(
                                             content if isinstance(content, bytes) else content.encode("utf-8")
                                         )
-                                    preview_path = (
-                                        os.path.splitext(save_path)[0] + ".webp"
+                                    preview_path = os.path.join(
+                                        get_preview_dir(save_path),
+                                        os.path.splitext(os.path.basename(save_path))[0] + ".webp",
                                     )
 
                                     optimized_data, _ = ExifUtils.optimize_image(
@@ -2788,9 +2796,7 @@ class DownloadManager:
                             entry = cast(Any, adjusted_entry)
                             metadata_entries[index] = entry
 
-                metadata_file_path = (
-                    os.path.splitext(entry.file_path)[0] + ".metadata.json"
-                )
+                metadata_file_path = get_metadata_path(entry.file_path)
                 metadata_files_for_cleanup.append(metadata_file_path)
 
                 await MetadataManager.save_metadata(entry.file_path, entry)
@@ -3049,7 +3055,11 @@ class DownloadManager:
         extension = os.path.splitext(preview_path)[1] or ".webp"
 
         targets = [
-            os.path.splitext(entry.file_path)[0] + extension for entry in entries
+            os.path.join(
+                get_preview_dir(entry.file_path),
+                os.path.splitext(os.path.basename(entry.file_path))[0] + extension,
+            )
+            for entry in entries
         ]
 
         if not targets:

py/services/metadata_sync_service.py

@@ -12,6 +12,7 @@ from ..services.settings_manager import SettingsManager
 from ..utils.civitai_utils import resolve_license_payload
 from ..utils.model_utils import determine_base_model
 from ..utils.models import autov3_from_civitai_files
+from ..utils.sidecar_paths import get_metadata_path
 from .connectivity_guard import OFFLINE_FRIENDLY_MESSAGE, is_expected_offline_error
 from .errors import RateLimitError
 from .model_sources import has_external_source
@@ -216,7 +217,7 @@ class MetadataSyncService:
             logger.error(error)
             return False, error
 
-        metadata_path = os.path.splitext(file_path)[0] + ".metadata.json"
+        metadata_path = get_metadata_path(file_path)
         enable_archive = self._settings.get("enable_metadata_archive_db", False)
         previous_source = model_data.get("metadata_source") or (model_data.get("civitai") or {}).get("source")
 
@@ -485,7 +486,7 @@ class MetadataSyncService:
                 + (f" with version: {model_version_id}" if model_version_id else "")
             )
 
-        metadata_path = os.path.splitext(file_path)[0] + ".metadata.json"
+        metadata_path = get_metadata_path(file_path)
         await self.update_model_metadata(
             metadata_path,
             metadata,
@@ -505,7 +506,7 @@ class MetadataSyncService:
     ) -> Dict[str, Any]:
         """Apply metadata updates and persist to disk and cache."""
 
-        metadata_path = os.path.splitext(file_path)[0] + ".metadata.json"
+        metadata_path = get_metadata_path(file_path)
         metadata = await metadata_loader(metadata_path)
 
         for key, value in updates.items():
@@ -554,7 +555,7 @@ class MetadataSyncService:
         }
 
         expected_hash: Optional[str] = None
-        first_metadata_path = os.path.splitext(file_paths[0])[0] + ".metadata.json"
+        first_metadata_path = get_metadata_path(file_paths[0])
         first_metadata = await metadata_loader(first_metadata_path)
         if first_metadata and "sha256" in first_metadata:
             expected_hash = first_metadata["sha256"].lower()
@@ -565,7 +566,7 @@ class MetadataSyncService:
 
             try:
                 actual_hash = await hash_calculator(path)
-                metadata_path = os.path.splitext(path)[0] + ".metadata.json"
+                metadata_path = get_metadata_path(path)
                 metadata = await metadata_loader(metadata_path)
                 stored_hash = metadata.get("sha256", "").lower()
 

py/services/model_lifecycle_service.py

@@ -11,6 +11,7 @@ from ..services.service_registry import ServiceRegistry
 from ..services.pending_delete_service import get_pending_delete_service
 from ..utils.constants import PREVIEW_EXTENSIONS
 from ..utils.metadata_manager import MetadataManager
+from ..utils.sidecar_paths import get_metadata_path
 
 logger = logging.getLogger(__name__)
 
@@ -45,7 +46,10 @@ async def delete_model_artifacts(
 
     main_extension = ".safetensors" if main_extension is None else main_extension
     main_file = f"{file_name}{main_extension}" if main_extension else file_name
-    patterns = [main_file, f"{file_name}.metadata.json"]
+    patterns = [
+        main_file,
+        os.path.basename(get_metadata_path(os.path.join(target_dir, main_file))),
+    ]
     for ext in PREVIEW_EXTENSIONS:
         patterns.append(f"{file_name}{ext}")
 
@@ -260,7 +264,7 @@ class ModelLifecycleService:
 
         _require_path_in_library_roots(file_path, self._scanner, label="File path")
 
-        metadata_path = os.path.splitext(file_path)[0] + ".metadata.json"
+        metadata_path = get_metadata_path(file_path)
         metadata = await self._metadata_loader(metadata_path)
         metadata["exclude"] = True
 
@@ -315,7 +319,7 @@ class ModelLifecycleService:
         if not os.path.exists(file_path):
             raise ValueError("Model file does not exist")
 
-        metadata_path = os.path.splitext(file_path)[0] + ".metadata.json"
+        metadata_path = get_metadata_path(file_path)
         metadata_payload = await self._metadata_loader(metadata_path)
         metadata_payload["exclude"] = False
 
@@ -384,10 +388,11 @@ class ModelLifecycleService:
         if os.path.exists(new_file_path):
             raise ValueError("A file with this name already exists")
 
+        metadata_filename = os.path.basename(get_metadata_path(file_path))
         patterns = [
             f"{old_file_name}{old_extension}",
-            f"{old_file_name}.metadata.json",
-            f"{old_file_name}.metadata.json.bak",
+            metadata_filename,
+            f"{metadata_filename}.bak",
         ]
         for ext in PREVIEW_EXTENSIONS:
             patterns.append(f"{old_file_name}{ext}")
@@ -398,7 +403,7 @@ class ModelLifecycleService:
             if os.path.exists(path):
                 existing_files.append((path, pattern))
 
-        metadata_path = os.path.join(target_dir, f"{old_file_name}.metadata.json")
+        metadata_path = get_metadata_path(file_path)
         metadata: Optional[Dict[str, object]] = None
         hash_value: Optional[str] = None
 

py/services/model_scanner.py

@@ -11,6 +11,7 @@ from ..utils.models import BaseModelMetadata, autov3_from_civitai_files
 from ..config import config
 from ..utils.file_utils import find_preview_file, get_preview_extension, calculate_sha256, calculate_autov3
 from ..utils.metadata_manager import MetadataManager
+from ..utils.sidecar_paths import get_metadata_path, get_preview_dir
 from ..utils.civitai_utils import resolve_license_info
 from .model_cache import ModelCache
 from .model_hash_index import ModelHashIndex
@@ -1709,7 +1710,7 @@ class ModelScanner:
             file_path = item.get("file_path")
             if not file_path:
                 continue
-            metadata_path = f"{os.path.splitext(file_path)[0]}.metadata.json"
+            metadata_path = get_metadata_path(file_path)
             if not os.path.exists(metadata_path):
                 continue
             try:
@@ -2339,7 +2340,7 @@ class ModelScanner:
                         target_associated_path = os.path.join(target_path, new_associated_filename)
                         
                         # Store metadata file path for special handling
-                        if file == f"{base_name}.metadata.json":
+                        if file == os.path.basename(get_metadata_path(source_path)):
                             source_metadata = source_file_path
                             moved_metadata_path = target_associated_path
                         else:
@@ -2399,7 +2400,7 @@ class ModelScanner:
             metadata['file_name'] = os.path.splitext(os.path.basename(model_path))[0]
             
             if 'preview_url' in metadata and metadata['preview_url']:
-                preview_dir = os.path.dirname(model_path)
+                preview_dir = get_preview_dir(model_path)
                 # Update preview filename to match the new base name
                 new_base_name = os.path.splitext(os.path.basename(model_path))[0]
                 preview_ext = get_preview_extension(metadata['preview_url'])
@@ -2759,7 +2760,7 @@ class ModelScanner:
 
             # Sidecar write-back: JSON null encodes the checked-unavailable
             # state. Skip silently when the sidecar does not exist.
-            metadata_path = f"{os.path.splitext(file_path)[0]}.metadata.json"
+            metadata_path = get_metadata_path(file_path)
             if os.path.exists(metadata_path):
                 with open(metadata_path, 'r', encoding='utf-8') as handle:
                     payload = json.load(handle)

py/services/pending_delete_service.py

@@ -38,6 +38,7 @@ from typing import (
 )
 
 from ..utils.constants import PREVIEW_EXTENSIONS
+from ..utils.sidecar_paths import get_metadata_path
 from ..utils import settings_paths
 
 logger = logging.getLogger(__name__)
@@ -669,7 +670,10 @@ class PendingDeleteService:
         """Enumerate existing artifacts exactly like delete_model_artifacts."""
         main_extension = ".safetensors" if main_extension is None else main_extension
         main_file = f"{file_name}{main_extension}" if main_extension else file_name
-        patterns = [main_file, f"{file_name}.metadata.json"]
+        patterns = [
+            main_file,
+            os.path.basename(get_metadata_path(os.path.join(target_dir, main_file))),
+        ]
         for ext in PREVIEW_EXTENSIONS:
             patterns.append(f"{file_name}{ext}")
 

py/services/preview_asset_service.py

@@ -10,6 +10,7 @@ from urllib.parse import urlparse
 from ..utils.constants import CARD_PREVIEW_WIDTH, PREVIEW_EXTENSIONS
 from ..utils.civitai_utils import rewrite_preview_url
 from ..utils.preview_selection import resolve_mature_threshold, select_preview_media
+from ..utils.sidecar_paths import get_metadata_path, get_preview_dir
 from .settings_manager import get_settings_manager
 
 logger = logging.getLogger(__name__)
@@ -159,7 +160,7 @@ class PreviewAssetService:
         """Replace an existing preview asset for a model."""
 
         base_name = os.path.splitext(os.path.basename(model_path))[0]
-        folder = os.path.dirname(model_path)
+        folder = get_preview_dir(model_path)
 
         extension, optimized_data = await self._convert_preview(
             preview_data, content_type, original_filename
@@ -179,7 +180,7 @@ class PreviewAssetService:
         with open(preview_path, "wb") as handle:
             handle.write(optimized_data)
 
-        metadata_path = os.path.splitext(model_path)[0] + ".metadata.json"
+        metadata_path = get_metadata_path(model_path)
         metadata = await metadata_loader(metadata_path)
         metadata["preview_url"] = preview_path
         metadata["preview_nsfw_level"] = nsfw_level

py/services/tag_update_service.py

@@ -2,10 +2,9 @@
 
 from __future__ import annotations
 
-import os
-
 from typing import Awaitable, Callable, Dict, List, Sequence, Tuple
 
+from ..utils.sidecar_paths import get_metadata_path
 from .auto_tag_service import extract_auto_tags
 
 
@@ -24,8 +23,7 @@ class TagUpdateService:
         update_cache: Callable[[str, str, Dict[str, object]], Awaitable[bool]],
     ) -> Tuple[List[str], List[str]]:
         """Add tags to a metadata entry and return updated tags and auto_tags."""
-        base, _ = os.path.splitext(file_path)
-        metadata_path = f"{base}.metadata.json"
+        metadata_path = get_metadata_path(file_path)
         metadata = await metadata_loader(metadata_path)
 
         raw_tags = metadata.get("tags", [])

py/services/use_cases/filename_template_use_case.py

@@ -12,6 +12,7 @@ import os
 from typing import Any, Awaitable, Callable, Dict, List, Optional, Sequence
 
 from ...utils.constants import AUTO_ORGANIZE_BATCH_SIZE
+from ...utils.sidecar_paths import get_metadata_path
 from ...utils.utils import calculate_filename_for_model
 from ..model_file_service import AutoOrganizeResult, ProgressCallback
 from ..model_lifecycle_service import ModelLifecycleService, load_local_metadata
@@ -200,7 +201,7 @@ class FilenameTemplateUseCase:
         sidecar or no ``original_file_name`` entry exists (models never
         renamed, or renamed before the recording shipped).
         """
-        metadata_path = f"{os.path.splitext(file_path)[0]}.metadata.json"
+        metadata_path = get_metadata_path(file_path)
         metadata = await self._metadata_loader(metadata_path)
         original = metadata.get("original_file_name")
         if not isinstance(original, str):

py/utils/metadata_manager.py

@@ -8,6 +8,7 @@ from typing import Any, Dict, Optional, Type, Union, cast
 from .models import BaseModelMetadata, CheckpointMetadata, EmbeddingMetadata, LoraMetadata
 from .file_utils import normalize_path, find_preview_file, calculate_sha256, calculate_autov3
 from .lora_metadata import extract_lora_metadata, extract_checkpoint_metadata
+from .sidecar_paths import get_metadata_path, resolve_metadata_path
 
 logger = logging.getLogger(__name__)
 
@@ -32,7 +33,7 @@ class MetadataManager:
             - metadata: BaseModelMetadata instance or None
             - should_skip: True if corrupted metadata file exists and model should be skipped
         """
-        metadata_path = f"{os.path.splitext(file_path)[0]}.metadata.json"
+        metadata_path = get_metadata_path(file_path)
         
         # Check if metadata file exists
         if not os.path.exists(metadata_path):
@@ -98,11 +99,7 @@ class MetadataManager:
                 payload.update(unknown_fields)
         else:
             if not should_skip:
-                metadata_path = (
-                    file_path
-                    if file_path.endswith(".metadata.json")
-                    else f"{os.path.splitext(file_path)[0]}.metadata.json"
-                )
+                metadata_path = resolve_metadata_path(file_path)
                 if os.path.exists(metadata_path):
                     try:
                         with open(metadata_path, "r", encoding="utf-8") as handle:
@@ -150,7 +147,7 @@ class MetadataManager:
             return model_data
 
         folder = model_data.get("folder")
-        metadata_path = f"{os.path.splitext(file_path)[0]}.metadata.json"
+        metadata_path = get_metadata_path(file_path)
         sidecar_exists = os.path.exists(metadata_path)
         cached = model_data.copy()
         payload = await MetadataManager.load_metadata_payload(file_path)
@@ -188,12 +185,7 @@ class MetadataManager:
           bool: Success or failure
         """
         # Determine if the input is a metadata path or a model file path
-        if path.endswith('.metadata.json'):
-            metadata_path = path
-        else:
-            # Use existing logic for model file paths
-            file_path = path
-            metadata_path = f"{os.path.splitext(file_path)[0]}.metadata.json"
+        metadata_path = resolve_metadata_path(path)
         temp_path = f"{metadata_path}.tmp"
         
         try:

py/utils/sidecar_paths.py

@@ -0,0 +1,215 @@
+"""Resolution of sidecar metadata and preview storage paths.
+
+All code that needs the on-disk location of a model's ``.metadata.json``
+sidecar or preview assets MUST go through these helpers instead of deriving
+paths inline (``splitext(model_path)[0] + ".metadata.json"`` and friends).
+
+Two storage modes are supported, selected by the ``sidecar_storage_mode``
+setting:
+
+- ``alongside`` (default): sidecars and previews live next to the model
+  file, the historical layout other tools may rely on.
+- ``centralized``: sidecars and previews live under a configurable root
+  (``sidecar_storage_path`` setting, default ``<settings_dir>/sidecars``),
+  mirroring the library-relative directory structure:
+  ``<root>/<library>/<root_basename>/<rel_dir>/<name>.metadata.json``.
+
+All helpers are pure path computations: no directory scans and no file I/O
+on the hot path. Settings lookups go through ``SettingsManager.get`` (a dict
+read); config roots come from the already-initialized ``config`` singleton.
+"""
+
+from __future__ import annotations
+
+import logging
+import os
+import re
+from typing import List, Optional
+
+logger = logging.getLogger(__name__)
+
+METADATA_SUFFIX = ".metadata.json"
+
+STORAGE_MODE_ALONGSIDE = "alongside"
+STORAGE_MODE_CENTRALIZED = "centralized"
+
+_VALID_MODES = frozenset({STORAGE_MODE_ALONGSIDE, STORAGE_MODE_CENTRALIZED})
+
+
+def _get_settings_value(key: str, default=None):
+    """Read a setting defensively; never fail path resolution on settings errors."""
+
+    try:
+        from ..services.settings_manager import get_settings_manager
+
+        value = get_settings_manager().get(key)
+    except Exception as exc:  # pragma: no cover - defensive fallback
+        logger.debug("sidecar_paths: settings lookup for %r failed: %s", key, exc)
+        return default
+    return default if value is None else value
+
+
+def get_storage_mode() -> str:
+    """Return the active sidecar storage mode (``alongside`` unless configured)."""
+
+    mode = _get_settings_value("sidecar_storage_mode", STORAGE_MODE_ALONGSIDE)
+    if mode not in _VALID_MODES:
+        return STORAGE_MODE_ALONGSIDE
+    return mode
+
+
+def is_centralized() -> bool:
+    """Return True when centralized sidecar storage is active and resolvable."""
+
+    return get_storage_mode() == STORAGE_MODE_CENTRALIZED and bool(get_sidecar_root())
+
+
+def get_sidecar_root() -> str:
+    """Return the absolute root directory for centralized sidecar storage.
+
+    Empty string when centralized storage is not usable (mode alongside or an
+    unresolvable configured path).
+    """
+
+    if get_storage_mode() != STORAGE_MODE_CENTRALIZED:
+        return ""
+
+    configured = _get_settings_value("sidecar_storage_path", "")
+    if configured and isinstance(configured, str):
+        root = os.path.abspath(os.path.expanduser(configured.strip()))
+        if root:
+            return root
+
+    # Default: <settings_dir>/sidecars
+    try:
+        from .settings_paths import get_settings_dir
+
+        return os.path.join(get_settings_dir(), "sidecars")
+    except Exception as exc:  # pragma: no cover - defensive fallback
+        logger.warning("sidecar_paths: cannot resolve default sidecar root: %s", exc)
+        return ""
+
+
+def sanitize_path_component(name: str) -> str:
+    """Return a filesystem-safe single path component."""
+
+    safe = re.sub(r"[^A-Za-z0-9_.-]", "_", name or "")
+    return safe or "_"
+
+
+def _iter_model_roots() -> List[str]:
+    """Return every configured model root for the active library."""
+
+    try:
+        from ..config import config
+    except Exception as exc:  # pragma: no cover - defensive fallback
+        logger.debug("sidecar_paths: config unavailable: %s", exc)
+        return []
+
+    roots: List[str] = []
+    for attr in (
+        "loras_roots",
+        "base_models_roots",
+        "embeddings_roots",
+        "other_roots",
+        "extra_loras_roots",
+        "extra_checkpoints_roots",
+        "extra_unet_roots",
+        "extra_embeddings_roots",
+    ):
+        value = getattr(config, attr, None)
+        if value:
+            roots.extend(value)
+    return roots
+
+
+def _normalize_for_match(path: str) -> str:
+    return os.path.normpath(os.path.abspath(path))
+
+
+def resolve_centralized_dir(model_path: str) -> Optional[str]:
+    """Return the centralized mirror directory for ``model_path``.
+
+    The mirror layout is ``<sidecar_root>/<library>/<root_basename>/<rel_dir>``
+    where ``rel_dir`` is the model's directory relative to the model root that
+    contains it. The longest matching root wins so nested roots resolve to the
+    most specific mirror. Returns ``None`` when centralized storage is inactive
+    or the path is not under any configured model root.
+    """
+
+    root = get_sidecar_root()
+    if not root:
+        return None
+
+    target = _normalize_for_match(model_path)
+    model_dir = os.path.dirname(target)
+
+    best_root: Optional[str] = None
+    for candidate in _iter_model_roots():
+        if not candidate:
+            continue
+        normalized = _normalize_for_match(candidate)
+        if model_dir == normalized or model_dir.startswith(normalized + os.sep):
+            if best_root is None or len(normalized) > len(best_root):
+                best_root = normalized
+
+    if best_root is None:
+        return None
+
+    try:
+        from ..services.settings_manager import get_settings_manager
+
+        library = get_settings_manager().get_active_library_name() or "default"
+    except Exception:  # pragma: no cover - defensive fallback
+        library = "default"
+
+    rel_dir = os.path.relpath(model_dir, best_root)
+    parts = [root, sanitize_path_component(library), sanitize_path_component(os.path.basename(best_root))]
+    if rel_dir and rel_dir != os.curdir:
+        parts.extend(sanitize_path_component(part) for part in rel_dir.split(os.sep) if part not in ("", os.curdir))
+    return os.path.join(*parts)
+
+
+def get_sidecar_dir(model_path: str) -> str:
+    """Return the directory holding the model's sidecar/preview assets.
+
+    Centralized mode falls back to the model's own directory (with a warning)
+    when the path lies outside every configured model root.
+    """
+
+    if get_storage_mode() == STORAGE_MODE_CENTRALIZED:
+        mirror = resolve_centralized_dir(model_path)
+        if mirror:
+            return mirror
+        logger.warning(
+            "sidecar_paths: %s is outside configured model roots; storing sidecar alongside",
+            model_path,
+        )
+    return os.path.dirname(os.path.abspath(model_path))
+
+
+def get_metadata_path(model_path: str) -> str:
+    """Return the ``.metadata.json`` sidecar path for a model file."""
+
+    base_name = os.path.splitext(os.path.basename(model_path))[0] + METADATA_SUFFIX
+    return os.path.join(get_sidecar_dir(model_path), base_name)
+
+
+def is_metadata_path(path: str) -> bool:
+    """Return True when ``path`` already points at a metadata sidecar file."""
+
+    return path.endswith(METADATA_SUFFIX)
+
+
+def resolve_metadata_path(path: str) -> str:
+    """Accept either a model path or a sidecar path and return the sidecar path."""
+
+    if is_metadata_path(path):
+        return path
+    return get_metadata_path(path)
+
+
+def get_preview_dir(model_path: str) -> str:
+    """Return the directory holding the model's preview assets."""
+
+    return get_sidecar_dir(model_path)