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[Bug]: After Edit from here, ACP agents forget the conversation you kept #30136
Description
What happens
ACP agents (Grok, Kiro, Antigravity and the ACP registry agents) cannot shorten their own conversation, so rollbackThread ends the agent session and starts a fresh one. After Edit from here, the next turn resumes that empty session and sends only the new prompt. The agent no longer knows anything said before the edited message, although the thread still shows it.
Steps to reproduce (main cefb544af3)
- In an Antigravity thread, send "My favourite colour is teal", then "My favourite animal is an otter".
- Use Edit from here on the second prompt and send "What did I say first?". (The web hides the button for Antigravity, see [Bug]: Edit from here is hidden on Grok and Antigravity and offered on Muse, unlike what the server accepts #30137;
checkpoint.rollbackreaches the same path.) - The agent says it has no earlier message.
Cause
AcpProviderCapabilitiesV2 sets providerCanRollbackConversation: true, so the rollback looks native and turn start has no case for a session that holds none of the kept turns. The resume-fallback recovery handoff would also carry the rewound turns, because it does not skip rolled_back runs.
Expected
The agent answers from the kept conversation ("teal") and does not see the rewound prompt ("otter"). Providers that truncate natively (Codex, Claude, Pi, OpenCode) keep working as now, with no extra handoff.
I have a fix with a failing-first test, proven live with Antigravity on web and Android. I can open a PR if you want one.
Activity
Entrpi commentedon Nov 3, 2026
The fix is on our fork as one commit on top of
main(cefb544):415c024(compare).ACP now reports that it cannot truncate, the rollback policy accepts providers that can take a full-thread handoff instead, and the first turn after the rewind hands the fresh session the kept turns once, without the rolled-back ones. The failing test in
ProviderSwitch.integration.test.tsfails onmainfor this reason. Happy to open it as a PR if you want it.shivamhwp commentedon Nov 3, 2026
Issue watch found that Julius has already taken this over in #30188 at c4fa57c. It targets this issue and includes the kept-history handoff and rolled-back-run filtering. No duplicate changes were started, and I have not independently run its tests. Handing this issue-watch job over to that PR.