fix(acp): preserve persisted session history on save failures by Junass1 · Pull Request #13675 · NousResearch/hermes-agent

Junass1 · 2026-04-21T20:30:37Z

Summary

Add SessionDB.replace_messages() to atomically rewrite a session's messages.
Use the atomic replacement path for ACP session persistence.
Add regression coverage proving a failed ACP save does not erase previously persisted history.

Why

ACP session persistence previously cleared stored messages before appending the current in-memory history. If one of the later appends failed, for example because structured tool call data could not be serialized, the already persisted conversation was lost. That could break session restore after an editor/server restart.

The new path pre-serializes message fields before the write transaction, then deletes and inserts messages in one transaction. Bad input now leaves the previously persisted conversation intact.

Test Plan

uv run --extra dev python -m pytest tests/acp/test_session.py::TestPersistence::test_save_session_preserves_existing_messages_on_append_failure -q
uv run --extra dev python -m pytest tests/acp/test_session.py -q
git diff --check -- acp_adapter/session.py hermes_state.py tests/acp/test_session.py

ACP's save_session() did a non-atomic clear_messages() + append_message() loop. If any message hit an exception mid-loop (bad tool_call shape, etc.), the DELETE had already committed and the persisted conversation was lost. SessionDB.replace_messages() wraps DELETE + bulk INSERT in a single BEGIN IMMEDIATE transaction that rolls back on any exception, so a bad message can no longer clobber previously-persisted history. Salvages @Awsh1's PR #13675 — uses the existing replace_messages() helper (which covers more message fields than the PR's own copy) instead of adding a duplicate.

…ssages on encode failure

ACP's save_session() did a non-atomic clear_messages() + append_message() loop. If any message hit an exception mid-loop (bad tool_call shape, etc.), the DELETE had already committed and the persisted conversation was lost. SessionDB.replace_messages() wraps DELETE + bulk INSERT in a single BEGIN IMMEDIATE transaction that rolls back on any exception, so a bad message can no longer clobber previously-persisted history. Salvages @Awsh1's PR #13675 — uses the existing replace_messages() helper (which covers more message fields than the PR's own copy) instead of adding a duplicate.

…ssages on encode failure

ACP's save_session() did a non-atomic clear_messages() + append_message() loop. If any message hit an exception mid-loop (bad tool_call shape, etc.), the DELETE had already committed and the persisted conversation was lost. SessionDB.replace_messages() wraps DELETE + bulk INSERT in a single BEGIN IMMEDIATE transaction that rolls back on any exception, so a bad message can no longer clobber previously-persisted history. Salvages @Awsh1's PR NousResearch#13675 — uses the existing replace_messages() helper (which covers more message fields than the PR's own copy) instead of adding a duplicate.