When the gateway restarts mid-agent-work, the session transcript ends
on a tool result the agent never processed. Previously, the user had
to type 'continue' or use /retry (which replays from scratch, losing
all prior work).
Now, when the next user message arrives and the loaded history ends
with role='tool', a system note is prepended:
[System note: Your previous turn was interrupted before you could
process the last tool result(s). Please finish processing those
results and summarize what was accomplished, then address the
user's new message below.]
This is injected in _run_agent()'s run_sync closure, right before
calling agent.run_conversation(). The agent sees the full history
(including the pending tool results) and the system note, so it can
summarize what was accomplished and then handle the user's new input.
Design decisions:
- No new session flags or schema changes — purely detects trailing
tool messages in the loaded history
- Works for any restart scenario (clean, crash, SIGTERM, drain timeout)
as long as the session wasn't suspended (suspended = fresh start)
- The user's actual message is preserved after the note
- If the session WAS suspended (unclean shutdown), the old history is
abandoned and the user starts fresh — no false auto-continue
Also updates the shutdown notification message from 'Use /retry after
restart to continue' to 'Send any message after restart to resume
where it left off' — which is now accurate.
Test plan:
- 6 new auto-continue tests (trailing tool detection, no false
positives for assistant/user/empty history, multi-tool, message
preservation)
- All 13 restart drain tests pass (updated /retry assertion)
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