[Bug]: Revert restores files and timeline but leaves the reverted turns in the agent's context #6127

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/server

Steps to reproduce

1. Open a thread in a git workspace with the Claude provider and complete several turns.
2. Hover a user prompt a few turns back and use Revert to this message. Let the revert finish.
3. Confirm the visible rollback: the later turns are gone from the timeline and the workspace files are restored to the checkpoint.
4. Send a new prompt that probes memory rather than files, for example: quote verbatim the first five words of my previous prompt.

Expected behavior

After reverting to turn N, the provider session should continue from the conversation state at turn N. The reverted turns should be out of the model's context, so step 4 quotes the last retained prompt.

Actual behavior

The model answers with the prompt from a turn that was reverted away. The timeline and the workspace rolled back, but the agent's context did not: the underlying Claude session is resumed at the transcript leaf, so every reverted turn is still in the window.

This is quiet in the worst way. Nothing fails, nothing is logged, and the UI looks exactly right, so the natural assumption is that the model has forgotten what the timeline no longer shows. In my case the model then reasoned about work it had supposedly never done, and I only noticed because I happened to ask it to quote me.

Where it seems to come from, reading main:

• CheckpointReactor.ts:779 dispatches providerService.rollbackConversation after a successful file restore, which is the right intent.
• ClaudeAdapter.rollbackThread (ClaudeAdapter.ts:4482) truncates context.turns and refreshes the cursor, but context.lastAssistantUuid is left on the newest assistant message. updateResumeCursor (ClaudeAdapter.ts:1742) builds resumeSessionAt from that field, so the cursor keeps pointing past the revert. In my database it read turnCount: 9 next to a resumeSessionAt from a turn well after the revert point.
• Even with a correct value, resumeSessionAt never reaches the SDK: the query options built around ClaudeAdapter.ts:4101 pass resume only, and ClaudeAdapter.test.ts:3393 asserts options.resumeSessionAt === undefined under the name "passes Claude resume ids without pinning a stale assistant checkpoint".

I read that last test as deliberate, which is why I am filing this as one question rather than a patch: if the provider session cannot be resumed mid-transcript by design, then revert cannot mean what the timeline implies, and the gap probably belongs in the UI rather than in the adapter. Either direction is fine from where I sit. What is costly is the current silence.

Impact

Major degradation or frequent failure

Version or commit

Desktop 0.0.34-nightly.20260810.1061, source read at main @ 9c7622d

Environment

macOS 26.5.2, Claude provider (claudeAgent), Opus

Workaround

Fork the transcript by hand: copy the session .jsonl truncated at the last assistant message of the retained turn, give the copy a new session id, and point a thread at that session. The resumed context then ends where the timeline ends.