fix: upsert document vectors before pruning stale chunks

DocumentSyncService._index_vectors ran delete_by_filter on the
document's existing chunks FIRST and only then embedded; if the
embedding pass failed (Ollama down) the Paperless document was left
with zero vectors until the next successful sync - the same
zero-vector hazard already fixed for wiki pages in
VectorService.update_from_page.

Chunk ids are now deterministic uuid5 (document_{id}_chunk_{i}) so
re-upserting overwrites in place; new points are upserted first, then
stale points (including legacy random-uuid4 ones) are pruned via
scroll + delete_by_ids, and only after a successful upsert.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QbFZyDvYksazX6nYQYZ67L

src/services/document_sync_service.py

@@ -196,18 +196,6 @@ class DocumentSyncService:
         collection = get_qdrant_collection_name(user)
         await self.qdrant.ensure_collection(collection)
 
-        # Delete existing chunks for this document (via the async wrapper)
-        try:
-            await self.qdrant.delete_by_filter(
-                collection_name=collection,
-                filter_conditions={
-                    "doc_type": "document",
-                    "paperless_id": document_id,
-                }
-            )
-        except Exception as e:
-            logger.debug(f"No existing chunks to delete: {e}")
-
         # Chunk content
         chunks = self._chunk_text(content)
         if not chunks:
@@ -229,7 +217,11 @@ class DocumentSyncService:
                 )
                 continue
 
-            point_id = str(uuid.uuid4())
+            # Deterministic id: re-upserting the same document overwrites
+            # its previous chunks in place (enables delete-last below).
+            point_id = str(
+                uuid.uuid5(uuid.NAMESPACE_DNS, f"document_{document_id}_chunk_{i}")
+            )
             content_hash = hashlib.md5(chunk.encode()).hexdigest()
 
             points.append({
@@ -256,13 +248,38 @@ class DocumentSyncService:
                 f"(embedding failures); indexing the remaining {len(points)}"
             )
 
-        # Upsert to Qdrant in one batch via the async wrapper
+        # Upsert BEFORE pruning stale chunks (same order as the wiki
+        # reindex fix in VectorService.update_from_page): the old
+        # delete-first order left the document with ZERO vectors until the
+        # next successful sync whenever the embedding pass failed after the
+        # delete (e.g. Ollama down). Deterministic uuid5 ids make the
+        # in-place overwrite safe.
         if points:
             await self.qdrant.upsert_points(
                 collection_name=collection,
                 points=points
             )
 
+            # Prune chunks left over from a previous version of the document
+            # (indexes beyond the new count, or legacy random-uuid4 points).
+            # Only prune after a successful upsert - a fully failed embedding
+            # pass must not wipe the old vectors.
+            new_ids = {p["id"] for p in points}
+            existing = await self.qdrant.scroll_all_points(
+                collection_name=collection,
+                filter_conditions={
+                    "doc_type": "document",
+                    "paperless_id": document_id,
+                },
+                with_payload=False,
+            )
+            stale_ids = [pt["id"] for pt in existing if pt["id"] not in new_ids]
+            if stale_ids:
+                await self.qdrant.delete_by_ids(
+                    collection_name=collection,
+                    point_ids=stale_ids,
+                )
+
         return len(points)
 
     async def _index_graph(