Smart previews store the decoded source with the fitted colour matrix
baked in, but the file-local tone curve lives in the decoder's
SourceInfo, which a proxy did not keep: an offline ARW rendered and
exported with the generic filmic curve instead (darker, a different
look). The proxy header now carries the curve (validated on load,
ignored when invalid), DecodedSource::info_or merges it into the header
facts, and is_valid reads the longer header.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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