Four parsers (dvdsub, flac, lpcm, mpegaudio) stamp a source offset on
every frame but had no test that read one back, so a regression to
`source: None` would have been caught only by the brace-balanced audit
in codec/mod.rs — a lint, not a behavioural check. Each now asserts the
emitted frame carries the offset of the packet that supplied its first
byte.
The Blu-ray feed spans had no direct test at all. Add one that walks a
multi-item playlist and requires the spans to tile the feed with no gap
or overlap; it catches a one-sector-per-clip drift, which is exactly the
error class that would misattribute frames near a seam.
`no_provenance_still_places_by_marks` asserted only that placement
returned something, which passes for a frame placed in the wrong clip.
Its probe timestamp lands in an overlap between two clips in the real
mark table, so pinning one clip would assert a coin-flip; instead
require the offset to be one that a clip actually containing that
timestamp would produce.
Matthew Jackson
418abfe79e