## What changed
Use `thread/revert` to remove the selected turn and subsequent history, then restore the selected prompt in the composer. Keep the thread identity, settings, goal, and unrelated thread channels intact. Show a notice that conversation history was reverted and file changes are unchanged.
Resolve selections against persisted history, accounting for partially loaded transcripts and hidden review prompts. Reject stale selections and mid-turn steers. Refresh replay state and pagination after a revert, clear queued input and obsolete actions, and require a session reload when the revert cannot be confirmed.
## Testing
Add regression coverage for reverting earlier and first visible prompts in place, preserving unloaded history and thread state, rejecting steers in clipped history, and clearing streaming output, queued input, and stale approval actions.
GitOrigin-RevId: d3f0342539392bdbfec925d0c3d6f67369937f1b
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