push_all reads the file and reuses store_header and readable_store_format, the same pair a load
uses. The 96-byte prefix parser it replaces misread a str16 header and any str8 header past the
prefix as v1 and overwrote a store it could not read. Pins both encodings refused with the file
untouched.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>