Methods: exact live SHA preflight; atomic per-file install; installed synthetic regression suite; source archive round-trip; hardened local publisher contract; independent HTTP retry/cache-busting verification; append-only phase events plus current phase state; no live machine-close execution.
Collision rule: only byte-identical latest/old duplicates may be deduplicated. Any mismatch is blocking and rollback-safe.
Continuation rule: first incomplete phase is authoritative; completed core/publication phases are not repeated.
Limitations: this STEP does not exercise a real VM100/VM101/VM121 source publication; those paths are covered by synthetic contract fixtures and will receive their first live use in a later changing STEP.