- Log failed closes in _adopt_session_db_for_cached_agent with
logger.debug(..., exc_info=True) instead of bare pass, matching
_replace_session_db_in_kwargs so a failed close (EMFILE risk) is
diagnosable.
- Drop the fragile exec/source-slice fallback in the test helper import;
real import or pytest.skip. Source-level pins still cover reverts
without importing streaming.
Background subagents (delegate_tool) capture parent_agent._session_db by
reference. The cached-agent reuse path created a fresh SessionDB every
stream request and unconditionally closed the previous handle (PR #1421
EMFILE fix). A server-side wakeup / new turn for the same parent session
could therefore close the shared handle while children were still
flushing messages, producing:
Session DB append_message failed: 'NoneType' object has no attribute 'execute'
Reproduce (observed in production):
1. Parent WebUI session runs delegate_task with N background subagents
2. Parent turn tears down / idle-hook redelivers a deferred wakeup
3. New stream for the parent adopts a fresh SessionDB and closes the old one
4. Live subagents' append_message hits conn=None
Fix: _adopt_session_db_for_cached_agent reuses a still-open handle (and
closes the unused new one — still EMFILE-safe) and only replaces when
the existing handle is missing or already closed. Same guard applied to
_replace_session_db_in_kwargs (credential self-heal). LRU eviction still
closes at true session boundaries.
Tests updated to pin the adopt helper and the subagent-safe semantics.
carlotestor