Deleting the matched user message breaks the strict role-alternation
invariant on the exact incident tail this fix targets — user(confirm) →
assistant('OK, restarting') becomes two consecutive assistant messages,
which strict providers reject and which the alternation-repair passes
upstream don't cover. Replace the message content with an explicit
'confirmation EXPIRED, re-confirm before any destructive action'
sentinel instead: the trigger text is still neutralized, the model gets
an affirmative instruction not to act, and the message sequence stays
valid. Adds an alternation-preservation regression test.
Follow-up to the salvage of #59640 by @knoal.
When a high-risk side effect (e.g. host restart via shutdown.exe) runs,
the user's plain-text confirmation phrase is persisted in the conversation
transcript. If the host restart killed the gateway process before the
assistant's tool result was written, the transcript tail ends on the
assistant's text response - and the dangerous confirmation text remains
in the user role.
On the next inbound message - possibly a casual 'are you there?' from
the user minutes later - the LLM sees the stale confirmation and may
interpret the new turn as a fresh re-confirmation, re-executing the
destructive action. This is the failure mode reported in #59607.
Fix:
- Add strip_stale_dangerous_confirmations() in agent/replay_cleanup.py
that removes user messages whose content matches a known dangerous
confirmation pattern AND whose timestamp is older than 60 seconds.
- Add is_dangerous_confirmation() helper with the matched patterns
(i18n-aware: covers 確認強制重開機 from the original incident).
- Wire the stripper into _build_gateway_agent_history() right after the
existing 75ed07ace strippers, so the strip chain is:
strip_interrupted_tool_tails -> strip_dangling_tool_call_tail ->
strip_stale_dangerous_confirmations.
- Update _build_replay_entry() to preserve the timestamp on user
messages (it was previously dropped), since the new stripper needs it.
Complements 75ed07ace (which strips the assistant side of the broken
tail) by handling the user side: a stale plain-text confirmation that
the assistant has not yet responded to in a way the resume logic
recognises.
Failing-test-first discipline: the bug-detection test
test_stale_confirmation_text_is_stripped_on_resume fails on unfixed
code (proves the test catches the bug) and passes after the fix.
Five additional safety tests confirm no regression on:
- fresh confirmations (within expiry) are preserved
- non-confirmation text is preserved
- non-matching histories are untouched
- dangerous-pattern detection works in all cases (case, i18n, None)
- direct unit test of the strip helper
Refs: #59607
A WebUI/TUI session whose last turn died mid-tool-loop (stale-timeout kill,
interrupt, or process restart before the tool result was written) persists a
dangling assistant(tool_calls) or interrupted assistant->tool tail. The
messaging gateway already strips these tails before replay (the #49201 fix),
but the TUI/WebUI resume path fed db.get_messages_as_conversation() straight
in as the agent's conversation_history with no cleanup. The model re-issued
the unanswered call on every resume -- including after a full WebUI + Gateway
restart, since the poison lives in the SessionDB, not memory -- leaving the
session permanently 'thinking'. Only deleting the session recovered it.
- Extract the two strippers + helper from gateway/run.py into a shared
agent/replay_cleanup.py (sanitize_replay_history wraps both).
- gateway/run.py re-exports under the historical private names; messaging
behavior unchanged.
- Both TUI cold-resume sites now sanitize the model-fed history while leaving
the display transcript untouched, so the user still sees their full history.
Verified E2E against a real SessionDB: dangling and interrupted tails are
stripped from the model feed, healthy mid-progress tool sequences are
preserved, and the display transcript is always the full raw history.
