feat: add workspace rewind checkpoints

[Coiggahou2002]

Related Issue

Resolve #108

Problem

/undo restores conversation context, but files written by tool calls remain changed. Users therefore cannot safely rewind a turn as a unit, especially when the workspace is not a Git repository or already contains unrelated uncommitted work.

What changed

• Add /rewind [count], which previews and restores both conversation history and workspace files to their state before the selected prompt.
• Capture bounded, content-addressed checkpoints for the primary working directory and additional directories without depending on Git.
• Detect file conflicts after preview and abort before changing context; make filesystem restoration transactional and roll back a partial restore on failure.
• Keep /undo context-only while discarding the corresponding filesystem checkpoints so the two histories cannot become misaligned.
• Exclude ignored paths, symlinks, VCS metadata, dependencies, and checkpoint contents from session/debug exports.
• Document the command in English and Chinese and add a minor changeset.

The checkpoint store retains at most 20 turns and enforces limits of 50,000 files, 512 MiB per checkpoint, and 64 MiB per file. A failed checkpoint capture does not block the prompt, but it invalidates rewind alignment so stale state cannot be applied.

Verification

• Workspace checkpoint unit tests: 11 passed.
• Command registry/resolution tests: 32 passed.
• Targeted TUI rewind integration test passed; existing undo tests: 10 passed.
• Agent Core v1 export tests: 9 passed.
• Agent Core v2 export tests: 23 passed.
• Full monorepo typecheck passed.
• CLI and documentation builds passed.
• pnpm sherif passed.
• Lint completed with no errors (repository baseline warnings remain).

The full TUI message-flow suite otherwise reported six existing feedback attachment/media failures; the same failure was reproduced from an independent clean worktree without this change.

Checklist

• I have read the CONTRIBUTING document.
• I have linked a related issue, or explained the problem above.
• I have added tests that prove my feature works.
• Ran gen-changesets skill, or this PR needs no changeset.
• Ran gen-docs skill, or this PR needs no doc update.

[changeset-bot]

🦋 Changeset detected

Latest commit: 90f2c2d

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@moonshot-ai/kimi-code	Minor

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Keep rewind checkpoints aligned with mid-turn steers

This assumes the newest workspace checkpoints line up one-for-one with the newest undo anchors, but the streaming steerMessage() path still appends user transcript entries and calls session.steer directly without capturing a checkpoint. In a session with prompt A checkpointed and then a mid-turn steer B, /rewind 1 can offer B while prepareRewind(1) applies A's before-image and undoHistory(1) only removes B, restoring files too far back. Capture or invalidate checkpoints for the streaming steer path before using checkpointCount as an alignment guarantee.

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[liruifengv]

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