re: a music bank is two stems that play together -- not intro+loop, and

not something to concatenate

Q10, and it starts by withdrawing the question's own premise. BGM_001 is
not three sub-waves of 10 KB / 4.47 MB / 4.67 MB: the 10 KB is the bank
header. A bank is exactly TWO waves, and across all 32 BGM banks on the
disc the two always have the SAME duration -- equal to 0.01 s over
lengths from 37 s to 277 s. That alone kills intro+loop and kills two
halves of one piece, both of which require unequal lengths.

Four banks appear to break the rule and do not: BGM_106-109 are the known
leading-region straddle, and the giveaway is that the entry named
BGM_107.slb contains BANK id=1108. The seek packet counts pin each join
exactly, so they realign to the same two-equal-waves shape rather than
being dropped as noise. That trap goes in METHOD.

Then the roles, by decoding both waves to PCM. They are
sample-synchronous: transient-envelope correlation searched over +/-5 s
peaks at lag +0.00 s, and both waves stop at the same millisecond,
167.663 s. Two stems of one performance, meant to sound at once. Wave 1
is quieter, has almost no bass and is far more L/R-decorrelated, which
reads as a surround-rear pair or a second intensity layer -- I cannot
separate those two from the file, and say so: ChannelMask is 0x0002 on
both, and this game's channel metadata is already documented as
meaningless.

Two things the port needs that are NOT on the disc, both marked as
authored: the track is not a seamless loop (BGM_001 fades out and is
followed by 6.15 s of silence, no loop-point field found), and nothing
names which bank the menu plays -- all 32 BGM cues are numeric.

docs/re/METHOD.md

@@ -152,3 +152,11 @@ agent's loop prompt, i.e. nowhere durable. See [`README.md`](README.md) for the
   keeps rising long after the fade is over — 1.47 s against a declared 0.97 s on
   one screen. Time the fade from where the frame is *pure black*, and take the
   ramp itself from the keyframes.
+* **A `sound.pak` entry is not a bank.** Entry windows straddle bank boundaries
+  (the leading-region effect), so a naive "walk the RIFFs in this entry" gives
+  the tail of the previous bank, then one of your own, then the *next* bank's
+  header. It looks like a bank with the wrong number of waves. The tell is a
+  `BANK id=` that is not the entry's own number, and the fix is the `seek` packet
+  counts — they pin each wave's join exactly, so a straddle can be realigned
+  rather than thrown away. 4 of 32 BGM banks look like counterexamples until this
+  is applied.