strip_c2pa_boxes dropped a top-level C2PA uuid, AI-label XMP uuid or jumb
box. When that box precedes mdat, dropping it moves the coded data while
HEIF iloc and MP4 stco/co64 still hold the old absolute offsets, so a phone
HEIC laid out as ftyp, uuid (C2PA), mdat, meta came out undecodable.
Turn the box into a same-size free box with a zeroed payload instead, as
strip_isobmff_media_file already does for MP4/MOV.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>