feat(history): add native file and conversation rewind with redo

[S2thend]

Summary

Add native rewind and redo that restore captured workspace files and the persisted conversation together. This lets users return to an earlier prompt, retry an approach from its corresponding file state, and reverse a rewind.

• /rewind opens a prompt selector and, after confirmation, restores files and conversation to before the selected prompt.
• /redo restores the state before the last rewind, with support for multiple levels.
• /rewind-recover recovers an interrupted restore before the next prompt can proceed.

Checkpoints are captured before prompts, and supported local file tools preserve pre-edit contents, including the absence of newly created files. A new prompt clears redo. These commands do not call a model.

Implementation and compatibility

• Use the published filesnap = "=0.5.0" Rust crate in-process; no separate executable or Node/npm runtime is required.
• Preserve the existing per-file snapshot API and readability of legacy .snap files. New snapshots use content-addressed storage, and failed restores retain their checkpoint for retry.
• Write a durable recovery journal before restoring files, persist the destination conversation after successful file restoration, and then commit the history state. A workspace lock protects turns and restores from concurrent operations.
• Restore captured binary files as bytes. Coverage remains bounded by capture rules and pre-edit declarations: ignored, uncaptured, and remote resources are not guaranteed to be restored. Shell/MCP writes require their local files to have been captured beforehand.

Related to #1192, #232, and #432. Those completed issues provide the background for per-file undo and snapshots; this PR adds prompt-level file-and-conversation recovery and redo while retaining per-file compatibility.

The workflow draws on my own codex-rewind, which also integrates the engine in Rust, and pi-better-rewind-redo projects.

Related to #1192, #232, #432

Also related to Discussion #2631, where a user asks how to step back in a conversation. This PR adds explicit prompt-level rewind with corresponding file restoration and redo.

Validation

Validated on Linux with Rust 1.98.1 after rebasing onto daf8bf80:

• 891 tests passed, 1 skipped across forge_snaps, forge_repo, forge_services, and forge_main, using cargo nextest run --locked --offline --test-threads 2. The default-parallelism run had one runtime-heartbeat timing failure; the complete run passed with two test threads.
• All-target Clippy passed for those four crates with -D warnings.
• Locked debug CLI build and launcher --version/CLI --help checks passed.
• Changed Rust files pass formatting. Workspace-wide formatting still reports differences in unchanged upstream files.
• Manually verified file and conversation rewind/redo in the Linux TUI: create hello.py, add a greeting function, rewind to the earlier state, then redo to restore the function and its conversation state.

macOS and Windows runtime validation has not been performed locally.

Screenshots

Native command selection, including rewind, redo, and recovery:

Select the prompt whose preceding file and conversation state should be restored:

Confirm the rewind:

Rewind followed by redo restores the greeting-function conversation state. File contents were also checked during manual testing:

Co-Authored-By: ForgeCode noreply@forgecode.dev

[CLAassistant]

All committers have signed the CLA.