Closes the consumer halves of JR-044 and JR-045, which were blocked on
there being no reader at all. `AudioSignatureMatcher` implements the
specification's slide — ±600 frames, scoring the fraction of overlapping
frames whose peak band agrees — and returns the tier and offset.
JR-045: `TryParseFrames` refuses any prefix but `v1:`. A `v2:` signature
from a future producer describes a DSP chain this build does not
implement, so scoring it as v1 would be a confident wrong answer where
declining is a correct one — the item drops to the runtime tier, which is
the entire reason the prefix is separate from `schema_version`.
JR-044: a runtime under 120 s yields no match and therefore no offset,
read off the runtime rather than inferred from a missing string, because
the runtime is what both producers test. The boundary is asserted on one
file at 119.999 s and 120.000 s, so a null cannot be blamed on the decode.
The offset has two terms, which is easy to miss: the recovered slide, and
the difference between where the two windows are anchored, since both are
centred on their own file's midpoint. A release carrying 40 s of extra
head material recovers 20 s from each.
One parameter is not from the specification and is marked as such in the
code: an alignment must overlap by at least 64 frames before its score
counts, or the extreme offsets compare a handful of frames where a chance
agreement scores 1.0 and beats the true alignment.
TRACES: JR-044, JR-045 | SR-003
