* fix(artwork): serve images whose format has no registered decoder
The new pipeline derives dimensions, mime and the placeholder hashes at
resolution time, so a decode became a precondition for recording artwork at
all. An image in a format Go has no decoder for therefore failed acquisition,
retried until the 12h budget ran out, and then settled as absent, serving a
placeholder from that point on. The old pipeline decoded only to resize and
fell back to the original bytes when that failed, so these covers used to work.
A local file is picked by matching an image extension, so bytes it cannot
decode are most likely a codec we lack: image.ErrFormat on a folder, upload or
embedded source now yields an Artwork row carrying just the hash and mime, and
the bytes stay servable. An external response carries no such guarantee, so it
still fails and retries rather than pinning a non-image body as a cover. A
corrupt image of a known format and an over-cap declared size still fail, so
the decompression bomb guard is unchanged. Absent rows recorded by earlier
builds are re-resolved by the existing stale-absent recheck within a day, so
no epoch bump is needed to repair them.
Reusing a stored image now re-decodes when it carries no dimensions, so a
row recorded while a decoder was missing can still be upgraded later.
Registers jxl, heic and heif in mime_types.yaml: image detection resolves the
extension through the host MIME table, and the Alpine release image ships no
/etc/mime.types, so those covers were never recorded in folder.ImageFiles
there and never reached the pipeline at all.
* fix(artwork): never record empty bytes as artwork
image.DecodeConfig returns image.ErrFormat for an empty payload just as it
does for a codec with no registered decoder, so a zero-byte cover file was
recorded as found artwork and served as an empty response instead of falling
back to the placeholder. A truncated image of a known format already fails
with unexpected EOF rather than ErrFormat, so only the empty case needed the
guard.
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