diff --git a/__init__.py b/__init__.py
index cf317063..5223fc45 100644
--- a/__init__.py
+++ b/__init__.py
@@ -1,13 +1,32 @@
-from .py.lora_manager import LoraManager
-from .py.nodes.lora_loader import LoraManagerLoader, LoraManagerTextLoader
-from .py.nodes.trigger_word_toggle import TriggerWordToggle
-from .py.nodes.lora_stacker import LoraStacker
-from .py.nodes.save_image import SaveImage
-from .py.nodes.debug_metadata import DebugMetadata
-from .py.nodes.wanvideo_lora_select import WanVideoLoraSelect
-from .py.nodes.wanvideo_lora_select_from_text import WanVideoLoraSelectFromText
-# Import metadata collector to install hooks on startup
-from .py.metadata_collector import init as init_metadata_collector
+try:  # pragma: no cover - import fallback for pytest collection
+    from .py.lora_manager import LoraManager
+    from .py.nodes.lora_loader import LoraManagerLoader, LoraManagerTextLoader
+    from .py.nodes.trigger_word_toggle import TriggerWordToggle
+    from .py.nodes.lora_stacker import LoraStacker
+    from .py.nodes.save_image import SaveImage
+    from .py.nodes.debug_metadata import DebugMetadata
+    from .py.nodes.wanvideo_lora_select import WanVideoLoraSelect
+    from .py.nodes.wanvideo_lora_select_from_text import WanVideoLoraSelectFromText
+    from .py.metadata_collector import init as init_metadata_collector
+except ImportError:  # pragma: no cover - allows running under pytest without package install
+    import importlib
+    import pathlib
+    import sys
+
+    package_root = pathlib.Path(__file__).resolve().parent
+    if str(package_root) not in sys.path:
+        sys.path.append(str(package_root))
+
+    LoraManager = importlib.import_module("py.lora_manager").LoraManager
+    LoraManagerLoader = importlib.import_module("py.nodes.lora_loader").LoraManagerLoader
+    LoraManagerTextLoader = importlib.import_module("py.nodes.lora_loader").LoraManagerTextLoader
+    TriggerWordToggle = importlib.import_module("py.nodes.trigger_word_toggle").TriggerWordToggle
+    LoraStacker = importlib.import_module("py.nodes.lora_stacker").LoraStacker
+    SaveImage = importlib.import_module("py.nodes.save_image").SaveImage
+    DebugMetadata = importlib.import_module("py.nodes.debug_metadata").DebugMetadata
+    WanVideoLoraSelect = importlib.import_module("py.nodes.wanvideo_lora_select").WanVideoLoraSelect
+    WanVideoLoraSelectFromText = importlib.import_module("py.nodes.wanvideo_lora_select_from_text").WanVideoLoraSelectFromText
+    init_metadata_collector = importlib.import_module("py.metadata_collector").init
 
 NODE_CLASS_MAPPINGS = {
     LoraManagerLoader.NAME: LoraManagerLoader,
diff --git a/docs/architecture/model_routes.md b/docs/architecture/model_routes.md
index d32420dd..00329299 100644
--- a/docs/architecture/model_routes.md
+++ b/docs/architecture/model_routes.md
@@ -9,77 +9,119 @@ exposed in `py/routes/base_model_routes.py`, the collaborators it leans on, and
 any cache or WebSocket side effects implemented in
 `py/utils/routes_common.py`.
 
+## Contents
+
+- [Handler catalogue](#handler-catalogue)
+- [Dependency map and contracts](#dependency-map-and-contracts)
+  - [Cache and metadata mutations](#cache-and-metadata-mutations)
+  - [Download and WebSocket flows](#download-and-websocket-flows)
+  - [Read-only queries](#read-only-queries)
+  - [Template rendering and initialization](#template-rendering-and-initialization)
+
 ## Handler catalogue
 
-| Endpoint(s) | Handler | Purpose | Collaborators | Cache / WebSocket side effects |
-| --- | --- | --- | --- | --- |
-| `/{prefix}` | `handle_models_page` | Renders the HTML page for a model type, populating the template from cached scanner data when available. | `settings`, `server_i18n`, `service.scanner.get_cached_data()` | Reads scanner cache to build folder list; flags initialization state without mutating cache. |
-| `/api/lm/{prefix}/list` | `get_models` | Returns paginated model metadata. | `service.get_paginated_data()`, `service.format_response()` | None (read-only). |
-| `/api/lm/{prefix}/delete` | `delete_model` | Removes a single model from disk and cache. | `ModelRouteUtils.handle_delete_model()` | Deletes files, prunes `scanner.get_cached_data().raw_data`, calls `cache.resort()`, and updates `scanner._hash_index`. |
-| `/api/lm/{prefix}/exclude` | `exclude_model` | Marks a model as excluded so it no longer appears in listings. | `ModelRouteUtils.handle_exclude_model()` | Updates metadata, decrements `scanner._tags_count`, removes cache entry and hash index entry, and appends to `scanner._excluded_models`. |
-| `/api/lm/{prefix}/fetch-civitai` | `fetch_civitai` | Fetches metadata for a specific model from CivitAI. | `ModelRouteUtils.fetch_and_update_model()` | Uses scanner cache to find the target record and updates it via `scanner.update_single_model_cache`. |
-| `/api/lm/{prefix}/fetch-all-civitai` | `fetch_all_civitai` | Bulk refreshes metadata for models missing CivitAI info. | `ModelRouteUtils.fetch_and_update_model()`, `ws_manager.broadcast()` | Streams progress to all clients, updates cache entries, optionally resorts cached data. |
-| `/api/lm/{prefix}/relink-civitai` | `relink_civitai` | Re-associates a local file with a CivitAI entry. | `ModelRouteUtils.handle_relink_civitai()` | Updates metadata, refreshes cache via `scanner.update_single_model_cache`. |
-| `/api/lm/{prefix}/replace-preview` | `replace_preview` | Replaces the preview asset attached to a model. | `ModelRouteUtils.handle_replace_preview()` | Writes new preview file, updates metadata, and calls `scanner.update_preview_in_cache()`. |
-| `/api/lm/{prefix}/save-metadata` | `save_metadata` | Persists edits to model metadata. | `ModelRouteUtils.handle_save_metadata()` | Saves metadata file and syncs the cache entry. |
-| `/api/lm/{prefix}/add-tags` | `add_tags` | Adds or increments tags for a model. | `ModelRouteUtils.handle_add_tags()` | Mutates metadata, increments `scanner._tags_count`, and updates the cached model. |
-| `/api/lm/{prefix}/rename` | `rename_model` | Renames a model and its related assets. | `ModelRouteUtils.handle_rename_model()` | Renames files on disk, updates cache indices, refreshes metadata. |
-| `/api/lm/{prefix}/bulk-delete` | `bulk_delete_models` | Deletes multiple models in one request. | `ModelRouteUtils.handle_bulk_delete_models()` | Delegates to `scanner.bulk_delete_models()` which removes disk assets and cache records in bulk. |
-| `/api/lm/{prefix}/verify-duplicates` | `verify_duplicates` | Confirms that a list of files share the same hash. | `ModelRouteUtils.handle_verify_duplicates()` | Recalculates hashes, updates metadata, and patches cache entries when stored hashes change. |
-| `/api/lm/{prefix}/top-tags` | `get_top_tags` | Returns the most frequently used tags. | `service.get_top_tags()` | None (read-only). |
-| `/api/lm/{prefix}/base-models` | `get_base_models` | Lists base models referenced by this model type. | `service.get_base_models()` | None (read-only). |
-| `/api/lm/{prefix}/scan` | `scan_models` | Triggers a rescan of the filesystem. | `service.scan_models()` | Scanner rebuilds its cache as part of the service workflow. |
-| `/api/lm/{prefix}/roots` | `get_model_roots` | Enumerates root directories searched for this model type. | `service.get_model_roots()` | None (read-only). |
-| `/api/lm/{prefix}/folders` | `get_folders` | Returns cached folder summaries. | `service.scanner.get_cached_data()` | Reads cached structure without mutation. |
-| `/api/lm/{prefix}/folder-tree` | `get_folder_tree` | Builds a nested folder tree of cached items. | `service.scanner.get_cached_data()` | Reads cache; does not mutate. |
-| `/api/lm/{prefix}/unified-folder-tree` | `get_unified_folder_tree` | Returns a tree aggregating all roots. | `service.scanner.get_cached_data()` | Reads cache; does not mutate. |
-| `/api/lm/{prefix}/find-duplicates` | `find_duplicate_models` | Finds duplicate hashes within the cache. | `service.scanner.get_duplicates()`, `service.scanner.get_hash_by_filename()` | Uses cache data to assemble duplicate groups; no mutation. |
-| `/api/lm/{prefix}/find-filename-conflicts` | `find_filename_conflicts` | Groups models that share a filename across directories. | `service.scanner.get_filename_conflicts()`, `service.get_path_by_hash()` | Reads cache while formatting results. |
-| `/api/lm/{prefix}/get-notes` | `get_model_notes` | Retrieves saved notes for a model. | `service.get_model_notes()` | None (read-only). |
-| `/api/lm/{prefix}/preview-url` | `get_model_preview_url` | Resolves the static preview URL for a model. | `service.get_model_preview_url()` | None (read-only). |
-| `/api/lm/{prefix}/civitai-url` | `get_model_civitai_url` | Returns the CivitAI permalink for a model. | `service.get_model_civitai_url()` | None (read-only). |
-| `/api/lm/{prefix}/metadata` | `get_model_metadata` | Loads the raw metadata payload for a model. | `service.get_model_metadata()` | None (read-only). |
-| `/api/lm/{prefix}/model-description` | `get_model_description` | Returns a formatted description for the UI. | `service.get_model_description()` | None (read-only). |
-| `/api/lm/{prefix}/relative-paths` | `get_relative_paths` | Provides filesystem auto-complete suggestions. | `service.get_relative_paths()` | None (read-only). |
-| `/api/lm/{prefix}/civitai/versions/{model_id}` | `get_civitai_versions` | Lists remote versions and indicates which exist locally. | `get_default_metadata_provider()`, `self.service.has_hash()`, `self.service.get_path_by_hash()` | Read-only; consults cache/service indices to mark local availability. |
-| `/api/lm/{prefix}/civitai/model/version/{modelVersionId}` | `get_civitai_model_by_version` | Fetches detailed metadata for a specific CivitAI version. | `get_default_metadata_provider()` | None (read-only). |
-| `/api/lm/{prefix}/civitai/model/hash/{hash}` | `get_civitai_model_by_hash` | Fetches CivitAI details using a hash. | `get_default_metadata_provider()` | None (read-only). |
-| `/api/lm/download-model` (POST) & `/api/lm/download-model-get` (GET) | `download_model`, `download_model_get` | Starts a download through the shared download manager. | `ModelRouteUtils.handle_download_model()`, `ServiceRegistry.get_download_manager()` | The helper broadcasts download progress via `ws_manager.broadcast_download_progress()` and stores state in `ws_manager._download_progress`. |
-| `/api/lm/cancel-download-get` | `cancel_download_get` | Cancels an active download. | `ModelRouteUtils.handle_cancel_download()` | Broadcasts a cancellation message via `ws_manager.broadcast_download_progress()` and prunes download progress entries. |
-| `/api/lm/download-progress/{download_id}` | `get_download_progress` | Reports cached download progress for a download ID. | `ws_manager.get_download_progress()` | Read-only view of cached progress. |
-| `/api/lm/{prefix}/move_model` | `move_model` | Moves a model to a new folder. | `ModelMoveService.move_model()` | File operations performed by the injected service may update scanner caches downstream. |
-| `/api/lm/{prefix}/move_models_bulk` | `move_models_bulk` | Bulk move models to a new location. | `ModelMoveService.move_models_bulk()` | File operations delegated to the service. |
-| `/api/lm/{prefix}/auto-organize` (GET/POST) | `auto_organize_models` | Launches auto-organization for models, optionally limited to selected files. | `ModelFileService.auto_organize_models()`, `ws_manager.get_auto_organize_lock()`, `WebSocketProgressCallback` | Uses a shared asyncio lock, streams progress through `ws_manager.broadcast_auto_organize_progress()`, and relies on `ws_manager.is_auto_organize_running()` state. |
-| `/api/lm/{prefix}/auto-organize-progress` | `get_auto_organize_progress` | Polls the latest auto-organize progress snapshot. | `ws_manager.get_auto_organize_progress()` | Read-only view of the WebSocket manager’s cached progress. |
+The routes exposed by `BaseModelRoutes` combine HTTP wiring with a handful of
+shared helper classes.  Services surface filesystem and metadata operations,
+`ModelRouteUtils` bundles cache-sensitive mutations, and `ws_manager`
+coordinates fan-out to browser clients.  The tables below expand the existing
+catalogue into explicit dependency maps and invariants so refactors can reason
+about the expectations each collaborator must uphold.
 
-## Shared utility side effects
+## Dependency map and contracts
 
-The delegated helpers in `ModelRouteUtils` encapsulate most cache and
-WebSocket mutations.  The smoke tests in this repository exercise the
-following contracts from `py/utils/routes_common.py`:
+### Cache and metadata mutations
 
-* `handle_delete_model` removes matching records from
-  `scanner.get_cached_data().raw_data`, awaits `cache.resort()`, and calls
-  `scanner._hash_index.remove_by_path()` when an index is present before
-  returning a success payload.
-* `handle_replace_preview` writes a new preview file, persists metadata via
-  `MetadataManager.save_metadata()`, and then invokes
-  `scanner.update_preview_in_cache()` with the normalized preview path and
-  NSFW level so downstream requests surface the updated asset.
-* `handle_download_model` acquires the shared download manager from
-  `ServiceRegistry`, injects a WebSocket progress callback, and relies on
-  `ws_manager.broadcast_download_progress()` to update the cached progress map
-  that `get_download_progress` later reads.
-* `handle_bulk_delete_models`, `handle_add_tags`, `handle_exclude_model`, and
-  `handle_verify_duplicates` all mutate scanner-maintained collections (hash
-  indices, tag counts, exclusion lists, or cached metadata) so route handlers
-  can stay thin while cache consistency remains centralized in the utility
-  module.
-* `ws_manager.broadcast_auto_organize_progress()` stores the latest progress
-  snapshot consumed by `get_auto_organize_progress`, while
-  `ws_manager.broadcast()` is used to notify clients during CivitAI bulk
-  refreshes and other background operations.
+| Endpoint(s) | Delegate(s) | State touched | Invariants / contracts |
+| --- | --- | --- | --- |
+| `/api/lm/{prefix}/delete` | `ModelRouteUtils.handle_delete_model()` | Removes files from disk, prunes `scanner._cache.raw_data`, awaits `scanner._cache.resort()`, calls `scanner._hash_index.remove_by_path()`. | Cache and hash index must no longer reference the deleted path; resort must complete before responding to keep pagination deterministic. |
+| `/api/lm/{prefix}/exclude` | `ModelRouteUtils.handle_exclude_model()` | Mutates metadata records, `scanner._cache.raw_data`, `scanner._hash_index`, `scanner._tags_count`, and `scanner._excluded_models`. | Excluded models remain discoverable via exclusion list while being hidden from listings; tag counts stay balanced after removal. |
+| `/api/lm/{prefix}/fetch-civitai` | `ModelRouteUtils.fetch_and_update_model()` | Reads `scanner._cache.raw_data`, writes metadata JSON through `MetadataManager`, syncs cache via `scanner.update_single_model_cache`. | Requires a cached SHA256 hash; cache entries must reflect merged metadata before formatted response is returned. |
+| `/api/lm/{prefix}/fetch-all-civitai` | `ModelRouteUtils.fetch_and_update_model()`, `ws_manager.broadcast()` | Iterates over cache, updates metadata files and cache records, optionally awaits `scanner._cache.resort()`. | Progress broadcasts follow started → processing → completed; if any model name changes, cache resort must run once before completion broadcast. |
+| `/api/lm/{prefix}/relink-civitai` | `ModelRouteUtils.handle_relink_civitai()` | Updates metadata on disk and resynchronizes the cache entry. | The new association must propagate to `scanner.update_single_model_cache` so duplicate resolution and listings reflect the change immediately. |
+| `/api/lm/{prefix}/replace-preview` | `ModelRouteUtils.handle_replace_preview()` | Writes optimized preview file, persists metadata via `MetadataManager`, updates cache with `scanner.update_preview_in_cache()`. | Preview path stored in metadata and cache must match the normalized file system path; NSFW level integer is synchronized across metadata and cache. |
+| `/api/lm/{prefix}/save-metadata` | `ModelRouteUtils.handle_save_metadata()` | Writes metadata JSON and ensures cache entry mirrors the latest content. | Metadata persistence must be atomic—cache data should match on-disk metadata before response emits success. |
+| `/api/lm/{prefix}/add-tags` | `ModelRouteUtils.handle_add_tags()` | Updates metadata tags, increments `scanner._tags_count`, and patches cached item. | Tag frequency map remains in sync with cache and metadata after increments. |
+| `/api/lm/{prefix}/rename` | `ModelRouteUtils.handle_rename_model()` | Renames files, metadata, previews; updates cache indices and hash mappings. | File moves succeed or rollback as a unit so cache state never points to a missing file; hash index entries track the new path. |
+| `/api/lm/{prefix}/bulk-delete` | `ModelRouteUtils.handle_bulk_delete_models()` | Delegates to `scanner.bulk_delete_models()` to delete files, trim cache, resort, and drop hash index entries. | Every requested path is removed from cache and index; resort happens once after bulk deletion. |
+| `/api/lm/{prefix}/verify-duplicates` | `ModelRouteUtils.handle_verify_duplicates()` | Recomputes hashes, updates metadata and cached entries if discrepancies found. | Hash metadata stored in cache must mirror recomputed values to guarantee future duplicate checks operate on current data. |
+| `/api/lm/{prefix}/scan` | `service.scan_models()` | Rescans filesystem, rebuilding scanner cache. | Scanner replaces its cache atomically so subsequent requests observe a consistent snapshot. |
+| `/api/lm/{prefix}/move_model` | `ModelMoveService.move_model()` | Moves files/directories and notifies scanner via service layer conventions. | Move operations respect filesystem invariants (target path exists, metadata follows file) and emit success/failure without leaving partial moves. |
+| `/api/lm/{prefix}/move_models_bulk` | `ModelMoveService.move_models_bulk()` | Batch move behavior as above. | Aggregated result enumerates successes/failures while preserving per-model atomicity. |
+| `/api/lm/{prefix}/auto-organize` (GET/POST) | `ModelFileService.auto_organize_models()`, `ws_manager.get_auto_organize_lock()`, `WebSocketProgressCallback` | Writes organized files, updates metadata, and streams progress snapshots. | Only one auto-organize job may run; lock must guard reentrancy and WebSocket updates must include latest progress payload consumed by polling route. |
 
-Keeping these side effects in mind is essential when refactoring route logic:
-any replacement must continue to honor the implicit contracts the utilities
-expect from scanners, caches, and the WebSocket manager.
+### Download and WebSocket flows
+
+| Endpoint(s) | Delegate(s) | State touched | Invariants / contracts |
+| --- | --- | --- | --- |
+| `/api/lm/download-model` (POST) & `/api/lm/download-model-get` (GET) | `ModelRouteUtils.handle_download_model()`, `ServiceRegistry.get_download_manager()` | Schedules downloads, registers `ws_manager.broadcast_download_progress()` callback that stores progress in `ws_manager._download_progress`. | Download IDs remain stable across POST/GET helpers; every progress callback persists a timestamped entry so `/download-progress` and WebSocket clients share consistent snapshots. |
+| `/api/lm/cancel-download-get` | `ModelRouteUtils.handle_cancel_download()` | Signals download manager, prunes `ws_manager._download_progress`, and emits cancellation broadcast. | Cancel requests must tolerate missing IDs gracefully while ensuring cached progress is removed once cancellation succeeds. |
+| `/api/lm/download-progress/{download_id}` | `ws_manager.get_download_progress()` | Reads cached progress dictionary. | Returns `404` when progress is absent; successful payload surfaces the numeric `progress` stored during broadcasts. |
+| `/api/lm/{prefix}/fetch-all-civitai` | `ws_manager.broadcast()` | Broadcast loop described above. | Broadcast cadence cannot skip completion/error messages so clients know when to clear UI spinners. |
+| `/api/lm/{prefix}/auto-organize-progress` | `ws_manager.get_auto_organize_progress()` | Reads cached progress snapshot. | Route returns cached payload verbatim; absence yields `404` to signal idle state. |
+
+### Read-only queries
+
+| Endpoint(s) | Delegate(s) | State touched | Invariants / contracts |
+| --- | --- | --- | --- |
+| `/api/lm/{prefix}/list` | `service.get_paginated_data()`, `service.format_response()` | Reads service-managed pagination data. | Formatting must be applied to every item before response; pagination metadata echoes service result. |
+| `/api/lm/{prefix}/top-tags` | `service.get_top_tags()` | Reads aggregated tag counts. | Limit parameter bounded to `[1, 100]`; response always wraps tags in `{success: True}` envelope. |
+| `/api/lm/{prefix}/base-models` | `service.get_base_models()` | Reads service data. | Same limit handling as tags. |
+| `/api/lm/{prefix}/roots` | `service.get_model_roots()` | Reads configured roots. | Always returns `{success: True, roots: [...]}`. |
+| `/api/lm/{prefix}/folders` | `service.scanner.get_cached_data()` | Reads folder summaries from cache. | Cache access must tolerate initialization phases by surfacing errors via HTTP 500. |
+| `/api/lm/{prefix}/folder-tree` | `service.get_folder_tree()` | Reads derived tree for requested root. | Rejects missing `model_root` with HTTP 400. |
+| `/api/lm/{prefix}/unified-folder-tree` | `service.get_unified_folder_tree()` | Aggregated folder tree. | Returns `{success: True, tree: ...}` or 500 on error. |
+| `/api/lm/{prefix}/find-duplicates` | `service.find_duplicate_hashes()`, `service.scanner.get_cached_data()`, `service.get_path_by_hash()` | Reads cache and hash index to format duplicates. | Only returns groups with more than one resolved model. |
+| `/api/lm/{prefix}/find-filename-conflicts` | `service.find_duplicate_filenames()`, `service.scanner.get_cached_data()`, `service.scanner.get_hash_by_filename()` | Similar read-only assembly. | Includes resolved main index entry when available; empty `models` groups are omitted. |
+| `/api/lm/{prefix}/get-notes` | `service.get_model_notes()` | Reads persisted notes. | Missing notes produce HTTP 404 with explicit error message. |
+| `/api/lm/{prefix}/preview-url` | `service.get_model_preview_url()` | Resolves static URL. | Successful responses wrap URL in `{success: True}`; missing preview yields 404 error payload. |
+| `/api/lm/{prefix}/civitai-url` | `service.get_model_civitai_url()` | Returns remote permalink info. | Response envelope matches preview pattern. |
+| `/api/lm/{prefix}/metadata` | `service.get_model_metadata()` | Reads metadata JSON. | Responds with raw metadata dict or 500 on failure. |
+| `/api/lm/{prefix}/model-description` | `service.get_model_description()` | Returns formatted description string. | Always JSON with success boolean. |
+| `/api/lm/{prefix}/relative-paths` | `service.get_relative_paths()` | Resolves filesystem suggestions. | Maintains read-only contract. |
+| `/api/lm/{prefix}/civitai/versions/{model_id}` | `get_default_metadata_provider()`, `service.has_hash()`, `service.get_path_by_hash()` | Reads remote API, cross-references cache. | Versions payload includes `existsLocally`/`localPath` only when hashes match local indices. |
+| `/api/lm/{prefix}/civitai/model/version/{modelVersionId}` | `get_default_metadata_provider()` | Remote metadata lookup. | Errors propagate as JSON with `{success: False}` payload. |
+| `/api/lm/{prefix}/civitai/model/hash/{hash}` | `get_default_metadata_provider()` | Remote metadata lookup. | Missing hashes return 404 with `{success: False}`. |
+
+### Template rendering and initialization
+
+| Endpoint(s) | Delegate(s) | State touched | Invariants / contracts |
+| --- | --- | --- | --- |
+| `/{prefix}` | `handle_models_page` | Reads configuration via `settings`, sets locale with `server_i18n`, pulls cached folders through `service.scanner.get_cached_data()`, renders Jinja template. | Template rendering must tolerate scanner initialization by flagging `is_initializing`; i18n filter is attached exactly once per environment to avoid duplicate registration errors. |
+
+### Contract sequences
+
+The following high-level sequences show how the collaborating services work
+together for the most stateful operations:
+
+```
+delete_model request
+    → BaseModelRoutes.delete_model
+    → ModelRouteUtils.handle_delete_model
+        → filesystem delete + metadata cleanup
+        → scanner._cache.raw_data prune
+        → await scanner._cache.resort()
+        → scanner._hash_index.remove_by_path()
+```
+
+```
+replace_preview request
+    → BaseModelRoutes.replace_preview
+    → ModelRouteUtils.handle_replace_preview
+        → ExifUtils.optimize_image / config.get_preview_static_url
+        → MetadataManager.save_metadata
+        → scanner.update_preview_in_cache(model_path, preview_path, nsfw_level)
+```
+
+```
+download_model request
+    → BaseModelRoutes.download_model
+    → ModelRouteUtils.handle_download_model
+        → ServiceRegistry.get_download_manager().download_from_civitai(..., progress_callback)
+        → ws_manager.broadcast_download_progress(download_id, data)
+        → ws_manager._download_progress[download_id] updated with timestamp
+        → /api/lm/download-progress/{id} polls ws_manager.get_download_progress
+```
+
+These contracts complement the tables above: if any collaborator changes its
+behavior, the invariants called out here must continue to hold for the routes
+to remain predictable.
diff --git a/py/__init__.py b/py/__init__.py
index e69de29b..54e9a3f4 100644
--- a/py/__init__.py
+++ b/py/__init__.py
@@ -0,0 +1,12 @@
+"""Project namespace package."""
+
+# pytest's internal compatibility layer still imports ``py.path.local`` from the
+# historical ``py`` dependency.  Because this project reuses the ``py`` package
+# name, we expose a minimal shim so ``py.path.local`` resolves to ``pathlib.Path``
+# during test runs without pulling in the external dependency.
+from pathlib import Path
+from types import SimpleNamespace
+
+path = SimpleNamespace(local=Path)
+
+__all__ = ["path"]
diff --git a/tests/routes/test_base_model_routes_smoke.py b/tests/routes/test_base_model_routes_smoke.py
index f6674c08..bccd83a9 100644
--- a/tests/routes/test_base_model_routes_smoke.py
+++ b/tests/routes/test_base_model_routes_smoke.py
@@ -170,6 +170,8 @@ def test_replace_preview_writes_file_and_updates_cache(
             assert payload["preview_url"] == "/static/preview-model.webp"
             assert Path(expected_preview).exists()
             assert mock_scanner.preview_updates[-1]["preview_path"] == expected_preview
+            assert mock_scanner._cache.raw_data[0]["preview_url"] == expected_preview
+            assert mock_scanner._cache.raw_data[0]["preview_nsfw_level"] == 2
 
             updated_metadata = json.loads(metadata_path.read_text())
             assert updated_metadata["preview_url"] == expected_preview
@@ -204,6 +206,15 @@ def test_download_model_invokes_download_manager(
             progress = ws_manager.get_download_progress(payload["download_id"])
             assert progress is not None
             assert progress["progress"] == 42
+            assert "timestamp" in progress
+
+            progress_response = await client.get(
+                f"/api/lm/download-progress/{payload['download_id']}"
+            )
+            progress_payload = await progress_response.json()
+
+            assert progress_response.status == 200
+            assert progress_payload == {"success": True, "progress": 42}
             ws_manager.cleanup_download_progress(payload["download_id"])
         finally:
             await client.close()