[Pepps233]

Summary

Persist update_plan steps with stable IDs and optional success criteria while keeping the latest plan available in durable conversation history.

Return the complete resolved plan in successful tool results instead of appending a plan message to every model request, so ordinary requests can reuse the previous prompt prefix.

Reasoning

Appending an unsaved current-task message to each request moved that message when the next turn added conversation history, breaking prompt cache reuse.

Persisted tool results carry plan changes in the normal conversation.

Successful compaction summaries include the latest plan snapshot so the plan remains available after older tool results are compacted away.

The latest plan does not need to be the final message of every request.

Changes

• Add stable step IDs, optional success criteria, and single-step updates by ID to update_plan.
• Persist each resolved plan change and show IDs and criteria in the TUI.
• Include the complete resolved plan in successful model-visible tool results while keeping details.plan unchanged; clearing still returns Plan cleared.
• Remove the per-request plan message while preserving extension context transforms.
• Add the latest plan snapshot to successful, persisted compaction summaries; represent cleared or absent plans as an empty plan.
• Update the README and SDK documentation, with regression coverage for prefix reuse, resume, fork, compaction, and cancellation.

Testing

• Reproduced the prompt prefix break through session.prompt() with the faux provider before the fix.
• Focused Vitest run: 7 files, 110 tests passed.
• npm run check