Fix defunct Neo4j connection: add keep-alive, liveness check, retry on SessionExpired

graph_store/api.py

@@ -11,6 +11,20 @@ logger = logging.getLogger(__name__)
 router = APIRouter(prefix="/graph", tags=["graph"])
 
 
+@router.get("/nodes")
+async def graph_nodes(limit: int = 50) -> dict:
+    from graph_store.writer import get_driver
+    from graph_store.config import settings
+    driver = get_driver()
+    async with driver.session(database=settings.neo4j_database) as session:
+        result = await session.run(
+            "MATCH (n) WHERE NOT n:Chunk AND NOT n:Document RETURN labels(n)[0] AS label, n.name AS name LIMIT $limit",
+            limit=limit,
+        )
+        records = await result.data()
+    return {"count": len(records), "nodes": records}
+
+
 def _get_driver():
     from graph_store.writer import get_driver
     return get_driver()

graph_store/reader.py

@@ -76,10 +76,21 @@ LIMIT 20
 # ---------------------------------------------------------------------------
 
 async def _run_query(driver: AsyncDriver, cypher: str, **params) -> list[str]:
-    async with driver.session(database=settings.neo4j_database) as session:
-        result = await session.run(cypher, **params)
-        records = await result.data()
-        return [r["text"] for r in records if r.get("text")]
+    from neo4j.exceptions import SessionExpired
+    try:
+        async with driver.session(database=settings.neo4j_database) as session:
+            result = await session.run(cypher, **params)
+            records = await result.data()
+            return [r["text"] for r in records if r.get("text")]
+    except SessionExpired:
+        logger.warning("reader: SessionExpired — resetting driver and retrying")
+        from graph_store.writer import close_driver, get_driver
+        await close_driver()
+        driver = get_driver()
+        async with driver.session(database=settings.neo4j_database) as session:
+            result = await session.run(cypher, **params)
+            records = await result.data()
+            return [r["text"] for r in records if r.get("text")]
 
 
 async def _union_queries(driver: AsyncDriver, queries: list[tuple[str, dict]]) -> list[str]:

graph_store/stream.py

@@ -34,6 +34,10 @@ async def graph_stream(websocket: WebSocket):
     driver = AsyncGraphDatabase.driver(
         settings.neo4j_uri,
         auth=(settings.neo4j_username, settings.neo4j_password),
+        max_connection_lifetime=1800,
+        connection_acquisition_timeout=30,
+        keep_alive=True,
+        liveness_check_timeout=10,
     )
     try:
         async with driver.session(database=settings.neo4j_database) as session:

graph_store/writer.py

@@ -107,6 +107,10 @@ def get_driver() -> AsyncDriver:
         _driver = AsyncGraphDatabase.driver(
             settings.neo4j_uri,
             auth=(settings.neo4j_username, settings.neo4j_password),
+            max_connection_lifetime=1800,
+            connection_acquisition_timeout=30,
+            keep_alive=True,
+            liveness_check_timeout=10,
         )
     return _driver