diff --git a/docs/re/f6-unit2-parent-alpha-multiplies.md b/docs/re/f6-unit2-parent-alpha-multiplies.md
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+# F6 unit 2 — the parent's alpha **IS** multiplied into the sweep leaf
+
+**Status: ✅ measured ⟨capture⟩.** 2026-09-02.
+
+**Question:** during the title build-in, does the sweep's drawn alpha follow the
+leaf alone, or leaf × parent?
+**Look at:** the sweep quad's drawn alpha. `pteff03`'s **leaf never goes below
+128** (keys `0:255 150:128 540:255 600:255`), so **any drawn alpha below 128 can
+only come from something else multiplying in.**
+**Not covered:** F5; the leaf's clock origin; where the sweep is on screen.
+
+---
+
+## The measurement
+
+One boot, one Ⓐ to skip the attract video, then no input — the title builds in
+undisturbed. `tools/re-capture/title_sweep_probe.sh`.
+
+The sweeps are the two rotated, 600 %-scaled strips, identified by size: **NDC
+1.38 × 3.15** and **1.39 × 3.15**, which is the corpus's own independently
+measured AABB height of **1134 px** (`2 × 1134 / 720 = 3.15`).
+
+```
+1.38 x 3.15   n=1140  frames  746..2499   alphas  8  24  33  50  58  74  83 100 107 …
+1.39 x 3.15   n= 614  frames  747..2498   alphas 16  41  67  91 116 128 129 130 131 …
+```
+
+> **Drawn alpha reaches 8.** `pteff03`'s leaf alpha is bounded below by **128**.
+> `8 < 128`, so the leaf cannot produce it alone. **The parent's alpha is
+> multiplied in.**
+
+## 🔴 This refutes the port's flagged decode — which is exactly what it asked for
+
+`screen_view.gd` records as decoded that *"the leaf runs on its OWN timeline and
+the parent's alpha is NOT multiplied in"*, and flags honestly that every
+observation behind it had parent alpha 0, so *"the leaf wins"* and *"the parent is
+ignored because it draws nothing"* were never separated — naming `t = 100…238` as
+the interval that would separate them.
+
+**This capture is in that interval and separates them: the parent is not ignored.**
+The port was right that its evidence could not tell the two apart, and right about
+which measurement would.
+
+📌 **And it bears on F6's original report.** The parent ramps `0→255` across
+`t=70→100`. If that multiplies in, the sweep is *invisible before t≈70 and dim
+until 100* — so a human reporting it "starts late" is seeing a real gate, even
+though `238…250` is an exit (unit 1). The gate is the parent's **entry** ramp, not
+the 238 cluster.
+
+## Reach
+
+⟨capture⟩, one boot, the two sweep quads identified **by size** against a
+previously measured AABB — not by name, since the draw stream carries no names.
+The bound argument needs only that `pteff03`'s leaf minimum is 128, which is
+⟨disc⟩. ⚠️ It does **not** establish the multiply is plain `leaf × parent` rather
+than some other combination that also dips below 128; it establishes that the
+parent participates.
diff --git a/tools/re-capture/title_sweep_probe.sh b/tools/re-capture/title_sweep_probe.sh
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+#!/usr/bin/env bash
+# F6 unit 2 -- capture the TITLE's build-in and read the sweep's drawn alpha.
+#
+# Discriminator: pteff03's LEAF declares alpha 255 from its own t=0, while its
+# PARENT ramps 0->255 across t=70..100. So in the drawn vertex colour:
+#     flat 255 throughout  => the parent is NOT multiplied in
+#     a ramp 0->255        => it IS
+# That also settles the port's own flagged ambiguity, whose stated separating
+# interval (t=100..238) is the same one F6 is about.
+#
+# Simpler than the menu probe on purpose: ONE A press to skip the attract video,
+# then no further input, so the title builds in undisturbed and stays.
+set -u
+export HOME=/sylph-home/re SDL_AUDIODRIVER=dummy DISPLAY=:98
+export XENIA_PAD_FILE=/tmp/xenia_pad.txt
+OUT="${1:-/sylph-home/re/f6}"; mkdir -p "$OUT"; rm -f "$OUT"/xenia_re_ui_draws_*.log
+pad(){ printf '%s' "$1" > "$XENIA_PAD_FILE.tmp"; mv "$XENIA_PAD_FILE.tmp" "$XENIA_PAD_FILE"; }
+pad ""
+( cd "$OUT" && nohup run-canary --log_ui_draws=true \
+    --ui_draw_capture_frames=2500 --ui_draw_capture_max=600000 \
+    >"$OUT/canary.stdout" 2>"$OUT/canary.stderr" & )
+sleep 8
+win="$(xdotool search --name "Xenia-canary" | tail -1)"
+[ -n "$win" ] || { echo "FATAL: no Xenia window"; pkill -x xenia_canary; exit 1; }
+xdotool windowactivate "$win" 2>/dev/null; xdotool key --window "$win" F10; xdotool key F10
+echo "armed at ${SECONDS}s"
+sleep 12; pad "press=A"; sleep 0.4; pad ""; echo "A (skip video) at ${SECONDS}s"
+sleep 45          # let the title build in and settle, no further input
+pkill -x xenia_canary
+echo "done at ${SECONDS}s"; ls -la "$OUT"/*.log 2>/dev/null