checkpoint: address Copilot review on the api/checkpoint facade
Commit

- Re-export the contract helper functions as thin wrapper funcs instead of exported vars, so the facade symbols can't be reassigned by consumers.
- Tighten the package doc: the contract avoids the heavy agent runtime/TUI and git-implementation packages, but does depend on leaf value packages (agent/types, checkpoint/id) and go-git plumbing — don't imply zero agent dep.
- Reword moved DTO comments that named private CLI internals (redactedJoinedPrompts/writeSessionToSubdirectory/ChunkTranscript/...) to describe behavior, since this is backend-facing contract documentation.
Co-Authored-By: Claude Opus 4.8 (1M context) noreply@anthropic.com Entire-Checkpoint: 907bd3ab830a
Checkpoints
can you look at this branch / pr also in the context of https://github.com/entireio/cli/issues/1433 and especially https://github.com/entireio/cli/issues/1433#issuecomment-4722283362
Claude CodeOpus 4.8[1m]
View sessionCheckpoint 1