fix: preserve full conversation history when restoring checkpoints before context compression

[roomote]

Summary

This PR attempts to address Issue #9308. When context compression occurs (either manually or automatically), the checkpoint system now preserves the full API conversation history alongside file checkpoints, allowing users to restore to the pre-compression state.

Problem

Previously, when context was compressed, the API conversation history was permanently modified. Restoring checkpoints would only restore file changes but not the conversation state, leaving users stuck with compressed context even when rolling back to earlier checkpoints.

Solution

1. API History Snapshots: Save the complete API conversation history alongside each checkpoint
2. Restore Full History: When restoring a checkpoint, also restore the associated API conversation history
3. Automatic Checkpoints: Create checkpoints automatically before context compression operations to preserve the full conversation

Changes

• Added saveApiHistorySnapshot() and restoreApiHistorySnapshot() methods to the checkpoint service
• Modified checkpoint save to include API history snapshots
• Modified checkpoint restore to restore API history when available (falls back to old behavior for existing checkpoints)
• Added automatic checkpoint creation before context compression operations
• Added comprehensive test coverage for the new functionality

Testing

• All existing checkpoint tests pass
• New tests added specifically for API history snapshot functionality
• Manual testing confirms that restoring checkpoints now properly restores pre-compression conversation state

Fixes #9308

Feedback and guidance are welcome!

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Important

This PR enhances the checkpoint system to save and restore full API conversation history, ensuring restoration of pre-compression states.

• Behavior:
  • Checkpoints now save and restore full API conversation history, preserving pre-compression state.
  • Automatic checkpoints created before context compression operations.
• Functions:
  • Adds saveApiHistorySnapshot() and restoreApiHistorySnapshot() to ShadowCheckpointService.
  • Modifies checkpointSave() and checkpointRestore() in index.ts to handle API history snapshots.
• Testing:
  • New tests in api-snapshots.spec.ts for API history snapshot functionality.
  • Updates to checkpoint.test.ts to mock new methods and test fallback behavior.

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[roomote]

Rooviewer   See task on Roo Cloud

Review completed. Found 1 issue that should be addressed:

• API history snapshot timing issue: The snapshot is saved after the checkpoint result is returned, but may be skipped if no file changes occurred. This could lead to inconsistent state where some checkpoints have snapshots and others don't.

_{Mention @roomote in a comment to request specific changes to this pull request or fix all unresolved issues.}

[roomote]

The API history snapshot is saved after awaiting the checkpoint result, but if checkpointResult is undefined (when saveCheckpoint returns undefined for no changes), the snapshot save will be skipped. This could lead to inconsistent state where some checkpoints have snapshots and others don't, even when the API history should be preserved. Consider saving the snapshot before returning, or ensure it's saved even when no file changes occurred but API history exists.

_{Fix it with Roo Code or mention @roomote and request a fix.}