Canonical Metadata Serialization

openmeta/exif_tiff_serialize.h exposes the deterministic target-neutral EXIF/TIFF serializer used by transfer preparation.

Call serialize_exif_tiff(store, {}) to obtain needed, allocate that many bytes, then call it again with the caller-owned span. Output is an unwrapped little-endian TIFF stream beginning with II and TIFF magic 42. It does not contain Exif\0\0 or container framing.

Current wrappers are:

Destination	Prepared EXIF payload
JPEG and current TIFF/DNG handoff	Exif\0\0 plus TIFF
PNG eXIf and WebP EXIF	TIFF
JP2/JXL/BMFF EXIF carrier	big-endian offset 6 plus Exif\0\0 plus TIFF

Preparation may allocate. Serialize once and retain immutable bytes for an allocation-free replay path. Repeated serialization against an immutable finalized store is deterministic and thread-safe.

For repeated fixed-width changes, openmeta/metadata_patch.h compiles exact key occurrences into opaque target-neutral handles. See Prepared metadata patching.

Validation and output bounds are enabled by default. Opaque MakerNotes are dropped unless explicitly preserved, and preservation does not reconstruct or relocate vendor-private tables. The host must still ensure that image-dependent metadata describes the actual encoded pixels.

See the complete contract in docs/canonical_serialization.md.