Creates a context checkpoint before exploratory work so you can later rewind and keep only a concise report.

Use this when you need to investigate with many intermediate tool calls (read/search/find/lsp/etc.) and want to minimize context cost afterward.

Rules:

• You MUST call rewind before yielding after starting a checkpoint.
• You MUST provide a clear goal explaining what you are investigating.
• You NEVER call checkpoint while another checkpoint is active.
• Not available in subagents.

Typical flow:

1. checkpoint(goal: …)
2. Perform exploratory work
3. rewind(report: …) with concise findings

After rewind, intermediate checkpoint messages are removed from active context and replaced by the report.