Saving (Cmd+S or auto-write) now merges LightCraft's properties into an
existing sidecar (lightcraft_meta::merge_xmp): owned properties (rating,
label, dc/IPTC/rights fields, lc:*) are replaced or removed, capture time
and GPS only when LightCraft has a value; everything else (crs:,
xmpMM:History, unknown namespaces, packet wrapper) is kept byte for byte.
The result is re-parsed and checked before it is written (temp + fsync +
rename). A sidecar that isn't valid XMP is copied to .xmp.bak-<time>
(never overwriting) before it is replaced; one that can't be read at all
is left alone and the save fails.
Shared stems: when several catalogued files map to one stem sidecar
(IMG.CR3 + IMG.JPG), it belongs to the raw (else the first by name) and
the others write and read <file>.xmp.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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