Fix datetime serialization in Obsidian metadata for pgvector

YAML frontmatter can contain datetime objects which aren't JSON
serializable. Add _make_serializable() to coerce all metadata values
before storing in pgvector.

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

blueprints/rag/logic.py

@@ -116,6 +116,17 @@ async def fetch_documents_from_paperless_ngx() -> list[Document]:
     return documents
 
 
+def _make_serializable(value):
+    """Convert a value to a JSON-serializable type."""
+    if isinstance(value, (str, int, float, bool, type(None))):
+        return value
+    if isinstance(value, (list, tuple)):
+        return [_make_serializable(v) for v in value]
+    if isinstance(value, dict):
+        return {k: _make_serializable(v) for k, v in value.items()}
+    return str(value)
+
+
 def _sanitize_text(text_content: str) -> str:
     """Strip non-printable and invalid characters that break embedding tokenizers."""
     # Remove null bytes and control characters (keep newlines and tabs)
@@ -174,8 +185,6 @@ async def fetch_obsidian_documents() -> list[Document]:
             parsed = obsidian_service.parse_markdown(content, md_path)
 
             # Create LangChain Document with obsidian source
-            document = Document(
-                page_content=parsed["content"],
             metadata = {
                 "source": "obsidian",
                 "filepath": parsed["filepath"],
@@ -187,7 +196,10 @@ async def fetch_obsidian_documents() -> list[Document]:
                     for k, v in parsed["metadata"].items()
                     if k not in ["created_at", "created_by"]
                 },
-                },
+            }
+            document = Document(
+                page_content=parsed["content"],
+                metadata=_make_serializable(metadata),
             )
             documents.append(document)
 
@@ -289,8 +301,6 @@ async def sync_obsidian_documents() -> dict[str, int]:
                 with open(filepath, "r", encoding="utf-8") as f:
                     content = f.read()
                 parsed = obsidian_service.parse_markdown(content, filepath)
-                document = Document(
-                    page_content=parsed["content"],
                 metadata = {
                     "source": "obsidian",
                     "filepath": parsed["filepath"],
@@ -302,7 +312,10 @@ async def sync_obsidian_documents() -> dict[str, int]:
                         for k, v in parsed["metadata"].items()
                         if k not in ["created_at", "created_by"]
                     },
-                    },
+                }
+                document = Document(
+                    page_content=parsed["content"],
+                    metadata=_make_serializable(metadata),
                 )
                 documents.append(document)
             except Exception as e: