Race scenario: a KG tool handler calls _get_kg() and gets a live
KnowledgeGraph; another thread fires tool_reconnect() between that
return and the handler's kg.add_triple()/kg.query_entity()/etc call.
tool_reconnect drains _kg_by_path and closes the underlying
sqlite3.Connection; the handler then raises sqlite3.ProgrammingError:
'Cannot operate on a closed database', which surfaces as a -32000
to the MCP client even though the user just asked for a reconnect.
New _call_kg(op) helper wraps each handler's kg call in a one-shot
retry: catch exactly sqlite3.ProgrammingError, evict the stale entry
(only if the cache slot still points at the closed instance — another
thread may have already replaced it), and rerun op against a fresh
_get_kg(). Beyond one retry give up so a sustained close-stream
surfaces clearly instead of looping.
All five KG handlers (tool_kg_query, tool_kg_add, tool_kg_invalidate,
tool_kg_timeline, tool_kg_stats) now route through _call_kg.
Tests pin the contract:
* retries with a fresh KG and returns the second result
* non-ProgrammingError exceptions propagate without retry
* gives up after exactly one retry on sustained close
mvalentsev
b8816e0fe2