Rollback Preview

PR-027 adds a non-mutating rollback preview for the supported patch-operation subset.

The command is:

prikk rollback-preview [path] [--ref REF]

--ref takes any published ref, not only a branch — a tag ref resolves through its tag object to the Block it names, so --ref tags/v1 previews the rollback of the tagged Block. See inverse planning, which shares the resolution.

The preview performs two read-only validations:

1. derive the unsigned inverse Patch payload for the supported operation subset;
2. replay the current target state from the supported single-parent block chain.

It then compares the current replayed state with the empty state before the replayed chain: rollback reaches back to the chain’s first block, and a checkpoint snapshot never moves that target. The result is a file-level preview of what rollback would need to create, delete, or replace.

No repository state is changed. The command does not write objects, append WAL records, publish refs, or modify the worktree.

Supported operation subset:

• CreateFile
• DeleteFile
• deterministic arbitrary-span EditText
• ReplaceBinary (DC-73)
• ChangePerm (DC-73)

Deferred:

• mutating rollback commands
• rollback ref publication policy
• authorization and audit policy for rollback
• commutation, confluence, and conflict witnesses
• plugin execution and remote sync