The same file exported from the library grid kept its camera, its lens,
its capture date and its rights statement. Exported from the develop
button it kept none of them, and `{date}` in a filename template
resolved to nothing at all. Two buttons, one photograph, two different
files -- and the develop one was the version the photographer had just
finished working on.
A session now remembers the header it was opened from, and
`open_session` takes that header rather than the orientation read out of
it, so a photograph cannot be opened for editing without saying which
file it came from. `render_open_frame` clones it onto
`Source::Rendered`; both arms of `export_one` -- the worker's own decode
and the frame handed over already rendered -- turn a header into a
`{date}` and a `SourceMetadata` through the same function, so the two
paths cannot come to different readings of one file. What of it actually
reaches the exported bytes is still decided inside `dr-export` from the
settings, which is what keeps the location-stripping option working here
rather than giving it a second implementation to disagree with.
The alternative was to hang the metadata on `Source::Rendered` alone and
keep it beside the session in the interface. That touches less, but it
makes the header and the pixels two cells to hold in step across the six
places an image is opened, replaced or fails to open, and the failure
mode of getting that pairing wrong is not a missing tag: it is one
photograph exported under another's byline and coordinates, silently.
Kept on the session, the two travel together or not at all.
The header is stored decoded rather than transcribed at open time,
deliberately. `dr-export` argues that source metadata is a parameter and
not a field on `Frame`, because two exports of one frame may legitimately
disclose different amounts; by the same reasoning a session may remember
where its pixels came from without that being a decision about what to
publish, and the allowlist that decides remains the single function in
`export.rs`.
A file with no header is left with none -- an empty `{date}` and nothing
for the encoder to copy -- rather than today's date standing in for a
capture time nobody recorded.
dtourolle
6acc98baad