Change preview_id to reference asset by reference ID, not content ID

Clients receive preview_id in API responses but could not dereference it
through public routes (which use reference IDs). Now preview_id is a
self-referential FK to asset_references.id so the value is directly
usable in the public API.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/assets/services/asset_management.py

@@ -116,7 +116,7 @@ def update_asset_metadata(
             set_reference_preview(
                 session,
                 reference_id=reference_id,
-                preview_asset_id=preview_id,
+                preview_reference_id=preview_id,
             )
             touched = True
 
@@ -202,7 +202,7 @@ def delete_asset_reference(
 
 def set_asset_preview(
     reference_id: str,
-    preview_asset_id: str | None = None,
+    preview_reference_id: str | None = None,
     owner_id: str = "",
 ) -> AssetDetailResult:
     with create_session() as session:
@@ -211,7 +211,7 @@ def set_asset_preview(
         set_reference_preview(
             session,
             reference_id=reference_id,
-            preview_asset_id=preview_asset_id,
+            preview_reference_id=preview_reference_id,
         )
 
         result = fetch_reference_asset_and_tags(

app/assets/services/ingest.py

@@ -11,10 +11,10 @@ from app.assets.database.queries import (
     add_tags_to_reference,
     fetch_reference_and_asset,
     get_asset_by_hash,
-    get_existing_asset_ids,
     get_reference_by_file_path,
     get_reference_tags,
     get_or_create_reference,
+    reference_exists,
     remove_missing_tag_for_asset_id,
     set_reference_metadata,
     set_reference_tags,
@@ -66,7 +66,7 @@ def _ingest_file_from_path(
 
     with create_session() as session:
         if preview_id:
-            if preview_id not in get_existing_asset_ids(session, [preview_id]):
+            if not reference_exists(session, preview_id):
                 preview_id = None
 
         asset, asset_created, asset_updated = upsert_asset(