handoff: Canary applies no gamma but does resample; the vertex stream is the cleaner oracle

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Jc4pciRArGHfxGGhEbwp5t

docs/port/HANDOFF.md

@@ -46,6 +46,48 @@ silent. A blank output is a failure, not an empty ask list.
 
 
 
+## ✅ 2026-09-02 (second) — **Canary applies NO gamma, but it DOES resample. Two measurement paths, only one has it**
+
+[`../re/canary-processing-between-guest-and-capture.md`](../re/canary-processing-between-guest-and-capture.md)
+
+Play-test question 3, from Canary's own source.
+
+**Gamma: none, on either side of the boundary.** `VdGetCurrentDisplayGamma` is
+declared `kStub` — it *reports* `kernel_display_gamma_type` (default 2, TV/BT.709)
+so the guest's D3D can build a ramp, and transforms nothing itself. And the guest
+does not build one for the splash: its dumped pixel shader is four ALU ops
+(`tfetch2D`, three `mul`, `max`) with **no `pow`, no ramp, no lookup**.
+
+**Geometry: yes.** `present_letterbox` defaults **true**, `present_safe_area_x/y`
+default **100** — so the guest's 1280×720 is scaled to fit the host window and
+letterboxed, nothing cropped. That is a **resample**, and it explains the
+1279×675 game surface the corpus has been measuring without accounting for it.
+
+### 🔴 The part that grades our evidence
+
+| path | route | Canary processing |
+|---|---|---|
+| **pixels** | guest draw → resolve → front buffer → **presenter (scale + letterbox)** → X11 → PNG | **a resample** |
+| **vertex stream** | guest CPU writes a vertex buffer → the draw logger reads guest memory | **none** |
+
+📌 **The per-frame alpha series I sent you is the second path** — read out of the
+guest's own vertex buffer before any shader, render target, resolve or presenter.
+That is why it can be stated as the game's values rather than as pixels we
+measured.
+
+⚠️ **Everything measured off a PNG carries the resample** — every RMSE against a
+capture, every glyph count, every surface mean, and the `motion-census` numbers on
+both sides. It does not invalidate them: a resample preserves *change*, which is
+what a motion census measures. It does mean **pixel-exact comparison runs through
+a filter nobody has characterised**, so where a question can be asked of the
+vertex stream instead, ask it there.
+
+❔ **Not measured:** the resample's actual filter. I read the cvars that say
+scaling happens, not the kernel that does it. And the no-gamma negative covers
+**the splash's shader only** — other screens' shaders are unchecked.
+
+---
+
 ## 🔴🔴 2026-09-02 — **THE GAME LERPS EVERY FRAME. And its splash is ALSO mostly frozen — your 3.2 s hold is CORRECT**
 
 [`../re/splash-interpolates-every-frame.md`](../re/splash-interpolates-every-frame.md)