Document safe helper adoption from older cloud checkouts
An older cloud checkout could not follow the document-draft guide without changing checkouts. Document how to reuse or obtain an authorised immutable public snapshot in existing task scratch, verify helper/test and shared-context prefix hashes, and run offline draft checks while preserving the working branch and governing files.
The procedure separates source delivery and synthetic checks from global installation, integration and instruction loading. No helper, policy or application behaviour changes.
Validation: formatting, runtime, diff integrity, documentation references/links/index/inventory, installed-lock parity and 58 policy-contract tests passed. Reused the existing 27-helper-test and 12-call CLI probe evidence against the identical helper/test hashes; decoded exports, stale-input rejection and original-file preservation were verified.