Why: Second-resolution release IDs let staging delete a previous release
when a same-source deployment ran within the same clock tick.
Evidence: Fixed-clock rollback regression fails before and passes after;
250 governance checks pass. Independent review replays collision and
copy-failure protection; receipts are in the primary task card.
Impact: Add invocation identity and exclusive directory creation; keep
old artifacts intact. Also retain the latest compatible frontend pointer.
Refs: User-approved I2; Dev #483; Frontend #71/#72
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