InStoreHold gains a cacheless flag: on re-entry of the same gate a cacheless call throws
instead of running, so the attach's hold (until it publishes Cache) and an enclosing store
call's user code cannot write the store behind the cache. Gate passes the flag; no field
mirrors Cache. Tests through a real attach and a nested cacheless write, a header pin for
attached variant stores, contract and CHANGELOG.
Builds on the previous commit; neither is built or run until the verify job.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>