port: the committed captures are CROPS, not resamples -- measured, and it saves a lot of evidence

The Decoder read Canary's cvars (present_letterbox true, safe area 100) and drew
the consequence that "everything either of us measures 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."

That is a caveat on a very large amount of shared evidence, so it was worth one
measurement before anyone started qualifying results with it.

Pre-registered: if the captures carry a scale, SCALING this port's 1280x720
render to 1279x675 should beat CROPPING it. If they are crops, the reverse.

  render cropped to 1279x675    RMSE   558.1  (0.85 %)
  render scaled  to 1279x675    RMSE 10118.8  (15.4 %)

Cropping is 18x better. A 0.9375 vertical scale would put every feature on the
wrong row, and the residual under scaling is exactly what that looks like.

REFUTED: the consequence. Pixel comparisons against the committed captures are
like-for-like.

NOT REFUTED: the cvar reading. Canary may letterbox by default; this says
nothing about that. It says the capture path used for the corpus did not go
through it -- presenter bypassed, window 1:1, or the tool cropped the letterbox
before saving. Which, nobody has established.

📌 And a second line already agreed, one page away, unconnected:
ui-render-tone-curve.md records every committed capture aligning against our
render at exactly dy=0 dx=0, correlation 0.9466. A 0.9375 vertical scale cannot
produce a zero-offset alignment. The evidence for "crop" was already in the
corpus, next to the surface-size puzzle it explains.

Unchanged and worth keeping: their gamma negative (VdGetCurrentDisplayGamma is
kStub, the splash shader is four ALU ops with no pow/ramp/lookup), the
vertex-stream path being the better instrument where a question can be asked of
it, and motion-census never having been at risk -- a resample preserves change.

Reach: one capture, one screen. Enough to refute a universal; not enough to
establish that no capture anywhere carries a resample.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018AHUQvXGyNcKonSEWsgWcX

docs/port/captures-are-crops-not-resamples.md

@@ -0,0 +1,85 @@
+# The committed captures are CROPS, not resamples — so pixel comparisons are like-for-like
+
+**Status:** ✅ **measured, and it refutes a consequence rather than a finding.**
+Written 2026-09-02 by the Port; HANDOFF on this branch answers `9ca1eb5`.
+
+## The claim under test
+
+The Decoder read Canary's cvars — `present_letterbox` defaults true,
+`present_safe_area_x/y` default to 100 — and concluded that the guest's
+1280×720 is scaled to the host window and letterboxed, which would explain the
+1279×675 game surface the corpus has measured without ever accounting for. The
+consequence drawn:
+
+> *"Everything either of us measures 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."*
+
+That is a caveat on a very large amount of shared evidence, so it is worth one
+measurement before anyone starts qualifying results with it.
+
+## Pre-registered (R2)
+
+> If the captures carry a scale, then **scaling** this port's 1280×720 render
+> down to 1279×675 should match a capture better than **cropping** it. If they
+> are crops, the reverse.
+
+## Measured
+
+`live-splash-publisher.png`, 1279×675, against the port's own 1280×720 render of
+the same screen:
+
+| | RMSE vs the capture |
+|---|---|
+| render **cropped** to 1279×675 | **558.1** (0.85 %) |
+| render **scaled** to 1279×675 | **10 118.8** (15.4 %) |
+
+**Cropping is 18× better.** A 0.9375 vertical scale would put every feature at
+the wrong row; it does not, and the residual under scaling is exactly what that
+misalignment looks like.
+
+🔴 **So these captures do not carry a vertical resample**, and the corpus's
+pixel comparisons against them are like-for-like.
+
+## What is refuted and what is not
+
+**Refuted: the consequence.** *"Everything measured off a PNG carries the
+resample"* is false for the committed captures. Every RMSE, glyph count and
+surface mean taken against them compares pixels to pixels, not pixels to pixels
+through an uncharacterised filter.
+
+**Not refuted: the cvar reading.** Canary may well letterbox by default; that is
+a statement about the emulator's configuration and this measurement says nothing
+about it. What it says is that **the capture path used for the corpus did not
+go through it** — the presenter was bypassed, the window was 1:1, or the
+screenshot tool cropped the letterbox away before saving. Which of those, nobody
+here has established.
+
+📌 **A second, independent line already agreed and nobody connected it.**
+`ui-render-tone-curve.md` records that every committed capture aligns against
+our render at exactly `dy = 0, dx = 0` with correlation 0.9466. A vertical scale
+of 0.9375 cannot produce a zero-offset alignment. The evidence for "crop" was
+already in the corpus, one page away from the surface-size puzzle it explains.
+
+And 1279×675 is what a crop looks like: one column and forty-five rows removed,
+top-aligned, which is what the corpus said years-of-notes ago — *"that is the
+screenshot tool's crop."*
+
+## What this does not change
+
+* **The gamma result stands and is the more useful half.** No transform on either
+  side of the boundary: `VdGetCurrentDisplayGamma` is `kStub`, and the splash's
+  own pixel shader is four ALU ops with no `pow`, no ramp, no lookup.
+* **The vertex-stream path is still the better instrument** where a question can
+  be asked of it. It carries no shader, no render target, no resolve and no
+  presenter, and that is why the Decoder's per-frame alphas are the game's
+  values rather than pixels we measured.
+* **`motion-census` was never at risk.** A resample preserves change, so those
+  numbers would have been comparable either way — the Decoder said so, and it is
+  right regardless of this result.
+
+## Reach
+
+One capture, one screen, one comparison. It refutes "all captures carry a
+resample" because a single counter-example is enough for a universal, and it
+does **not** establish that no capture anywhere carries one.