Use in-memory cache for obsidian indexed files instead of cross-engine DB query

The async/sync engine split caused visibility issues where newly indexed
files weren't found on the next cycle, triggering re-indexing of all 36
files every 60 seconds. Replace with a module-level dict that loads from
DB on cold start and stays in sync via cache updates after each indexing.

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

blueprints/rag/logic.py

@@ -10,7 +10,6 @@ from langchain_openai import OpenAIEmbeddings
 from langchain_postgres import PGVector
 from langchain_text_splitters import RecursiveCharacterTextSplitter
 from sqlalchemy import create_engine, text
-from sqlalchemy.ext.asyncio import create_async_engine
 
 from .fetchers import PaperlessNGXService
 from utils.obsidian_service import ObsidianService
@@ -64,13 +63,6 @@ def _get_engine():
     return _get_engine._engine
 
 
-def _get_async_engine():
-    """Get an async SQLAlchemy engine for direct queries."""
-    if not hasattr(_get_async_engine, "_engine"):
-        _get_async_engine._engine = create_async_engine(_pgvector_url)
-    return _get_async_engine._engine
-
-
 text_splitter = RecursiveCharacterTextSplitter(
     chunk_size=1000,  # chunk size (characters)
     chunk_overlap=200,  # chunk overlap (characters)
@@ -241,14 +233,18 @@ async def index_obsidian_documents():
     return {"indexed": len(documents)}
 
 
-async def _get_obsidian_indexed_files() -> dict[str, float]:
-    """Return {filepath: indexed_at} for all obsidian chunks in pgvector."""
+# In-memory cache of indexed obsidian files: {filepath: indexed_at}
+_obsidian_index_cache: dict[str, float] = {}
+
+
+def _load_obsidian_index_cache() -> dict[str, float]:
+    """Load indexed obsidian files from DB into cache (cold start only)."""
     collection_id = _get_collection_id()
     if not collection_id:
         return {}
-    engine = _get_async_engine()
-    async with engine.connect() as conn:
-        result = await conn.execute(
+    engine = _get_engine()
+    with engine.connect() as conn:
+        result = conn.execute(
             text(
                 "SELECT DISTINCT cmetadata->>'filepath' AS filepath, "
                 "MAX((cmetadata->>'indexed_at')::float) AS indexed_at "
@@ -270,8 +266,13 @@ async def sync_obsidian_documents() -> dict[str, int]:
     Returns:
         Dict with counts of added, updated, and deleted files.
     """
+    global _obsidian_index_cache
+
     obsidian_service = ObsidianService()
-    indexed_files = await _get_obsidian_indexed_files()
+
+    # Load cache from DB on first run
+    if not _obsidian_index_cache:
+        _obsidian_index_cache = _load_obsidian_index_cache()
 
     # Build map of current vault files -> mtime
     vault_files: dict[str, float] = {}
@@ -285,7 +286,7 @@ async def sync_obsidian_documents() -> dict[str, int]:
     # Find files to add or update
     files_to_index: list[str] = []
     for filepath, mtime in vault_files.items():
-        indexed_at = indexed_files.get(filepath)
+        indexed_at = _obsidian_index_cache.get(filepath)
         if indexed_at is None:
             files_to_index.append(filepath)
             added += 1
@@ -295,14 +296,16 @@ async def sync_obsidian_documents() -> dict[str, int]:
             files_to_index.append(filepath)
             updated += 1
 
-    # Find deleted files (in DB but not on disk)
-    for filepath in indexed_files:
+    # Find deleted files (in cache but not on disk)
+    for filepath in list(_obsidian_index_cache):
         if filepath not in vault_files:
             delete_documents_by_metadata("filepath", filepath)
+            del _obsidian_index_cache[filepath]
             deleted += 1
 
     # Index new/changed files
     if files_to_index:
+        now = time.time()
         documents = []
         for filepath in files_to_index:
             try:
@@ -314,7 +317,7 @@ async def sync_obsidian_documents() -> dict[str, int]:
                     "filepath": parsed["filepath"],
                     "tags": parsed["tags"],
                     "created_at": parsed["metadata"].get("created_at"),
-                    "indexed_at": time.time(),
+                    "indexed_at": now,
                     **{
                         k: v
                         for k, v in parsed["metadata"].items()
@@ -337,6 +340,10 @@ async def sync_obsidian_documents() -> dict[str, int]:
                 vector_store = _get_vector_store()
                 await vector_store.aadd_documents(documents=splits)
 
+        # Update cache for successfully processed files
+        for filepath in files_to_index:
+            _obsidian_index_cache[filepath] = now
+
     logger.info(
         f"Obsidian sync complete: {added} added, {updated} updated, {deleted} deleted"
     )