- Capture conversation_checkpoint_update from Cursor server (was ignored)
- Store checkpoint per conversationId, replay as conversation_state on next request
- Use protowire to embed raw checkpoint bytes directly (no deserialization)
- Extract session_id from Claude Code metadata for stable conversationId across resume
- Flatten conversation history into userText as fallback when no checkpoint available
- Use conversationId as session key for reliable tool call resume
- Add checkpoint TTL cleanup (30min)
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>