Snapshot Checkout Planning

PR-017 keeps a read-only snapshot checkout planning path.

The command:

prikk checkout --snapshot-plan [path] [--ref REF]

validates the current ref, target block, snapshot Blob object, and snapshot manifest paths. It does not write the worktree.

The current path-safety scaffold is deliberately conservative. It rejects:

• absolute paths
• . and .. components
• empty components
• backslashes and colon characters
• control characters
• Windows reserved names such as CON, NUL, COM1, and LPT1
• non-ASCII paths until Unicode NFC normalization is implemented
• duplicate paths and case-insensitive collisions

Use prikk checkout --snapshot-materialize to write validated snapshot files. Supported patch replay is available separately, while full patch algebra remains deferred. For exact validator rules, see path and worktree safety.