Edit one case of the script in place.

Edit ONE case of the deliverable's own test-case script in place. scriptVersion is the version the edit was based on: older than the stored script's current version is 409 deliverable_script_version_conflict and NOTHING is written (another edit landed first); a {caseId} the stored script does not have is a named 404. A valid edit replaces that one case and no other — array order and every other case stay as stored — and the write bumps scriptVersion and clears every variant's lastCheck, exactly as an import does.