diff --git a/docs/port/HANDOFF.md b/docs/port/HANDOFF.md
index 3b69722c..dc577775 100644
--- a/docs/port/HANDOFF.md
+++ b/docs/port/HANDOFF.md
@@ -720,6 +720,49 @@ human are the same item.** `sylpheed-cli screen render` deliberately does not
 rotate, which is why *both* renderers show it. That decision is still the
 human's, and it is in MISSION under "Needs a human decision — rotation".
 
+## ✅ 2026-08-29 — the leaf/parent alpha rule you asked for: THE LEAF WINS, do not multiply
+
+You said you would not guess it, which was right. Measured against the GPU draw
+capture, not against our renderer —
+[`ui-leaf-vs-parent-alpha.md`](../re/structures/ui-leaf-vs-parent-alpha.md).
+
+**Draw the leaf on its own timeline. Do NOT multiply the parent's alpha in.**
+
+The capture's vertex colours on the `ptloop` draw are `C3FFFFFF` / `B6FFFFFF` —
+alpha **195** and **182**. Fitting *only those two numbers* against the two leaf
+ramps gives one consistent time, **t = 355**:
+
+| | leaf at t=355 | observed |
+|---|---|---|
+| quad A alpha | **194.8** | **195** |
+| quad B alpha | **182.2** | **182** |
+| parent alpha | **0** | — |
+
+🔴 **Multiplying is refuted**: the parent has expired by t=355 (0 at t=250, and a
+group holds at its last keyframe), so `leaf × parent / 255` predicts **zero** and
+the sweeps would be invisible. They are drawn.
+
+✅ **The position check was predicted, not fitted** — no x entered the fit, and
+the same t places the quad centres at **981** and **478** against **992.0** and
+**467.2** measured off the capture. Four quantities, two differently-shaped
+ramps, one time.
+
+⚠️ **This is not a universal precedence rule, and your button case is the
+opposite one.** Here the parent is a container with **no sprite**. For a button,
+a base record's leaf *duplicates* the parent and the **parent wins**
+(`ui-button-focus-record.md`) — which `screen.rs` already knew. **The
+discriminator is which record actually carries the geometry.**
+
+❔ Not established: whether parent alpha would multiply in during a window where
+it is non-zero. Every observation here has parent = 0, so "leaf wins" and "parent
+ignored because it draws nothing" are not separated. A capture during t=100…238
+would separate them — say the word if that distinction ever costs you something.
+
+🟡 **And your `title_jp` `ptlogo_eff2` lead is a good one**, but I have not
+tested it: if its two-element leaf carries the geometry the same way, the 125 %
+scale may be the parent's and the leaf's real scale something else. That is the
+same shape as this finding and worth checking before authoring around it.
+
 ## Status
 
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