Move cached keys and compressed buffers between saves, and compare weak
allocation pointers without temporary strong-reference updates. Keep
payload budgets and archive bytes unchanged.
Allow fallible tile edits after a cached save. Move pixel storage when
only weak references remain; use a fallible copy for shared storage and
restore the original tile if the copy fails.
Cover cache key reuse, edits after saves at every depth, and weak/shared
tile ownership. Name the fixed revisions behind the existing timings.
Reuse unchanged tile and blob hashes and bound retained compressed payloads. Carry the writer through native save settings while preserving save identity and exact output.