handoff: BGM_103 as the menu music now has a runtime leg

The port asked for this to have its own line rather than sitting inside a drive
report, and they are right -- it is a third independent confirmation of a claim
that the port authors from.

The claim rested on GamePart_Title s sub_821C5580 playing cue 1103 (static code)
and on the bank s two declared wave sizes matching what an XMA probe saw (disc
census). On a driven boot, BGM_103 s two waves were handed to the XMA decoder at
the moment the main menu appeared -- observed being decoded on arrival at the
screen, rather than inferred from a table or matched by size afterwards.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QsEPXWVaEpyfudtR6re1Pd

docs/port/HANDOFF.md

@@ -666,6 +666,20 @@ finding stops resting on one asset. ⚠️ It needs a **driven, rendered** run
 capture will carry the ~10 % additive padding. `tools/re-capture/newgame_path.sh`
 drives to `SELECT DATA` and would need one more Ⓐ.
 
+## ✅ 2026-08-29 — `BGM_103` confirmed from the RUNTIME, a third independent leg
+
+"The menu's music is `BGM_103`" rested on two legs: `GamePart_Title`'s
+`sub_821C5580` playing cue 1103 (static code), and the bank's two declared wave
+sizes matching what an XMA probe saw (disc census). It now has a third, from a
+direction neither could reach.
+
+On a driven boot, **`BGM_103`'s two waves — 3 876 864 / 3 930 112 B — were
+handed to the XMA decoder at the moment the main menu appeared.** Not inferred
+from a cue table, not matched by size after the fact: observed being decoded, on
+arrival at the screen. Recorded in
+[`s00a-drive-blocked-by-focus.md`](../re/s00a-drive-blocked-by-focus.md), where
+it turned up incidentally.
+
 ## Status
 
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