diff --git a/docs/port/HANDOFF.md b/docs/port/HANDOFF.md
index 5fd8ee3..8299aa0 100644
--- a/docs/port/HANDOFF.md
+++ b/docs/port/HANDOFF.md
@@ -36,6 +36,7 @@ authored version can be deleted.
 | Q7 | transitions | ❔ open | |
 | Q8 | menu audio bindings | ❔ open | cue table complete, event binding is not |
 | Q9 | video binding + playback rules | 🟡 partial | `ADV.wmv` is the boot intro; new-game intro unidentified |
+| Q10 | music-bank sub-wave roles (intro+loop?) | ❔ open | we concatenate blindly today |
 | S1 | Ready Room go/no-go | ❔ open | probe not run |
 
 ## Already settled — the port can rely on these today
@@ -76,6 +77,11 @@ authored version can be deleted.
   reader must allow a short read there and only there.
 * **Voice downmixes to mono, music does not.** The left-channel downmix is correct
   for spoken lines and discards half a music mix.
+* **A music bank has several sub-waves and we glue them together.** `BGM_001`
+  is 10 KB + 4.47 MB + 4.67 MB, concatenated into one 347 s track. Nobody has
+  established whether those are intro + loop, two variations, or two halves —
+  see Q10. Do not build menu looping on the concatenated track until it is
+  answered.
 * **`JNGL_001.slb` does not decode.** One bank in 9 519; its payload is not a whole
   number of XMA1 packets from any known data offset.
 
diff --git a/docs/port/MISSION.md b/docs/port/MISSION.md
index d691adb..073a2b9 100644
--- a/docs/port/MISSION.md
+++ b/docs/port/MISSION.md
@@ -74,6 +74,7 @@ alongside it.
 | **Q7** | **Transitions.** What happens visually between screens — the `pteff00.prm` quads, a fade, a cut — and its timing | Described and timed against a capture |
 | **Q8** | **Menu audio.** Which BGM per screen; which cue on move / confirm / back / error. The cue table is complete; the event binding is not | Cue names bound to events, with how you established each |
 | **Q9** | **Video binding.** Which movie is the boot intro vs the new-game intro; whether playback is skippable and what ends it | Named movies plus the playback rules |
+| **Q10** | **What are a music bank's sub-waves?** `BGM_001.slb` is three sub-waves — 10 KB, 4.47 MB, 4.67 MB — and we currently **concatenate them blindly** into one 347 s track. Two near-equal halves could be intro + loop, or two variations, or two halves of one piece. A menu that loops its music needs to know which | The role of each sub-wave, established for at least the menu BGM. "Concatenate" is a decision, not a default — right now it is a default nobody chose |
 | **S1** | **Ready Room probe.** *Gated* — one iteration, then stop | A written go/no-go (see below) |
 
 ## Known unknowns — say so, do not fill them in
diff --git a/tools/re-capture/kf_time_probe.py b/tools/re-capture/kf_time_probe.py
new file mode 100755
index 0000000..a7f50cf
--- /dev/null
+++ b/tools/re-capture/kf_time_probe.py
@@ -0,0 +1,89 @@
+#!/usr/bin/env python3
+"""Per-frame quad geometry and vertex colour from a `log_ui_draws` capture.
+
+`ui_draw_order.py` answers "in what order were these painted"; this answers
+"what did this quad look like on frame N, and on N+1". That is what a keyframe
+TIME unit has to be measured against: the bundle says an element ramps from
+t=31 to t=34, and the only way to learn what a `t` is worth is to count the
+rendered frames the same ramp takes in the running game.
+
+    kf_time_probe.py <capture.log> [--csv out.csv]
+
+Emits one row per quad per frame: frame, draw index, pixel rect, whether the
+quad is axis-aligned, and the per-vertex colour word (whose alpha byte is the
+element's fade). Frame numbers are the emulator's VdSwap count, so they are
+SUBMITTED FRAMES, not wall-clock — which is the point: an emulator that runs
+at half speed does not move them.
+"""
+import re
+import sys
+
+W, H = 1280, 720
+VERT = re.compile(r"\[(-?\d+\.\d+),(-?\d+\.\d+),z=(-?\d+\.\d+)(?:,col=([0-9A-F]{8}))?\]")
+
+
+def quads(log):
+    """Yield (frame, draw, x0, y0, w, h, rot, col) for every quad in the log."""
+    frame, pending = None, None
+    for line in open(log):
+        if line.startswith("# every draw"):
+            frame = int(line.rstrip().split()[-1].split("..")[0])
+            continue
+        if line.startswith("--- frame"):
+            frame = int(line.split()[2])
+            continue
+        m = re.match(r"\s*(\d+) (prim=.*)", line)
+        if m:
+            pending = (int(m.group(1)), m.group(2))
+            continue
+        if "vb=0x" in line and pending:
+            hits = VERT.findall(line)
+            verts = [(float(a), float(b), c) for a, b, _z, c in hits]
+            if verts:
+                # Two conventions in one log: the UI sprite shader emits NDC,
+                # the full-screen pass emits pixels already.
+                if max(abs(v) for x, y, _c in verts for v in (x, y)) > 4.0:
+                    pts = [(x, y, c) for x, y, c in verts]
+                else:
+                    pts = [((x + 1) / 2 * W, (1 - y) / 2 * H, c) for x, y, c in verts]
+                per = 4 if "prim=13" in pending[1] else len(pts)
+                for q in range(0, len(pts), per):
+                    chunk = pts[q:q + per]
+                    if not chunk:
+                        continue
+                    xs = [p[0] for p in chunk]
+                    ys = [p[1] for p in chunk]
+                    x0, x1, y0, y1 = min(xs), max(xs), min(ys), max(ys)
+                    rot = all(
+                        (abs(x - x0) < 1.0 or abs(x - x1) < 1.0)
+                        and (abs(y - y0) < 1.0 or abs(y - y1) < 1.0)
+                        for x, y in zip(xs, ys)
+                    )
+                    cols = {p[2] for p in chunk if p[2]}
+                    col = sorted(cols)[0] if len(cols) == 1 else (
+                        "/".join(sorted(cols)) if cols else "")
+                    yield (frame, pending[0], round(x0), round(y0),
+                           round(x1 - x0), round(y1 - y0), "" if rot else "ROT",
+                           col)
+            pending = None
+
+
+def main():
+    log = sys.argv[1]
+    out = None
+    if "--csv" in sys.argv:
+        out = open(sys.argv[sys.argv.index("--csv") + 1], "w")
+        out.write("frame,draw,x,y,w,h,rot,col\n")
+    for row in quads(log):
+        line = "%d,%d,%d,%d,%d,%d,%s,%s" % row
+        if out:
+            out.write(line + "\n")
+        else:
+            print(line)
+    if out:
+        out.close()
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())
diff --git a/tools/re-capture/screen_build_capture.sh b/tools/re-capture/screen_build_capture.sh
new file mode 100755
index 0000000..8c0318b
--- /dev/null
+++ b/tools/re-capture/screen_build_capture.sh
@@ -0,0 +1,87 @@
+#!/usr/bin/env bash
+# Catch a screen being BUILT, not sitting still.
+#
+# `log_ui_draws` armed at the title only ever sees the steady state, and the
+# steady state is the one thing an animation question cannot be asked of. The
+# build — the wordmarks zooming in, the effect sprites wiping across, the black
+# fade lifting — happens in the seconds BEFORE the screen classifier can call it
+# a title.
+#
+# So arm repeatedly and keep every log: each F10 opens a new numbered file and
+# CLOSES the previous one (which stays on disk, complete). Re-arming every few
+# seconds through the boot therefore tiles the whole approach to the title, and
+# whichever file happens to straddle the build contains it. Stop re-arming the
+# instant the title is classified, so a press cannot land mid-build and abandon
+# the one file that matters.
+#
+# NO pad input at all. Ⓐ during the boot has ended a run on a permanent black
+# screen (docs/re/canary-scripted-input-traps.md), and nothing here needs it.
+#
+# Usage: screen_build_capture.sh [out_dir] [timeout_s]
+#   FRAMES=   frames per capture window (default 1200 ~ 20 s at 60 Hz)
+#   MAXDRAWS= hard stop per capture (default 80000)
+#   REARM=    seconds between F10 presses (default 10)
+set -u
+export HOME=/sylph-home/re SDL_AUDIODRIVER=dummy DISPLAY=:98
+SD="$(cd "$(dirname "$0")" && pwd)"
+OUT="${1:-/sylph-home/re/buildcap}"
+TIMEOUT="${2:-600}"
+mkdir -p "$OUT"; rm -f "$OUT"/xenia_re_ui_draws_*.log
+
+alive(){ ps -o pid=,stat= -C xenia_canary 2>/dev/null | awk '$2 !~ /^Z/ {print $1}'; }
+shot(){ screenshot "$1" >/dev/null 2>&1; }
+wide(){ [ "$(identify -format '%w' "$1" 2>/dev/null || echo 0)" -gt 1000 ]; }
+
+( cd "$OUT" && nohup run-canary \
+    --ui_draw_capture_frames="${FRAMES:-1200}" \
+    --ui_draw_capture_max="${MAXDRAWS:-80000}" \
+    --create_profile_if_none="${SYLPH_TAG:-SylphRE}" \
+    --logged_profile_slot_0_xuid="${SYLPH_XUID:-B13EBABEBABEBABE}" \
+    >"$OUT/canary.stdout" 2>"$OUT/canary.stderr" & )
+sleep 8
+until xdotool search --name "Xenia-canary" >/dev/null 2>&1; do
+  [ -n "$(alive)" ] || { echo "EMULATOR GONE before the window appeared"; exit 4; }
+  sleep 1
+done
+win="$(xdotool search --name "Xenia-canary" | tail -1)"
+echo "WINDOW=$win"
+
+arm(){
+  xdotool windowactivate "$win" 2>/dev/null
+  xdotool key --window "$win" F10 2>/dev/null
+  xdotool key F10 2>/dev/null
+}
+
+last_arm=-999
+deadline=$(( SECONDS + TIMEOUT ))
+s=none
+while [ $SECONDS -lt $deadline ]; do
+  [ -n "$(alive)" ] || { echo "EMULATOR GONE at ${SECONDS}s"; exit 4; }
+  shot /tmp/sbc.png
+  if [ -s /tmp/sbc.png ]; then
+    wide /tmp/sbc.png || { echo "GRAB IS NOT THE GAME SURFACE at ${SECONDS}s"; exit 6; }
+    s="$(python3 "$SD/screen_id.py" /tmp/sbc.png | awk '{print $1}')"
+  fi
+  if [ "$s" = "${WANT:-title}" ]; then
+    echo "t=${SECONDS}s $s  <- STOP re-arming"
+    cp /tmp/sbc.png "$OUT/reached.png"
+    break
+  fi
+  if [ $(( SECONDS - last_arm )) -ge "${REARM:-10}" ]; then
+    arm; last_arm=$SECONDS
+    echo "t=${SECONDS}s $s  (armed)"
+  else
+    echo "t=${SECONDS}s $s"
+  fi
+  sleep 1
+done
+
+# Let the straddling window run itself out rather than cutting it short.
+echo "waiting for the in-flight capture to close..."
+for _ in $(seq 1 40); do
+  grep -q "UI-CAP. done" "$OUT/canary.stdout" 2>/dev/null && break
+  sleep 1
+done
+grep -i "UI-CAP" "$OUT/canary.stdout" | tail -6
+ls -l "$OUT"/xenia_re_ui_draws_*.log 2>/dev/null || echo "NO CAPTURE LOG"
+echo "SCREEN BUILD CAPTURE DONE (screen=$s, emulator left running)"