Revert "fix(web): composite consumes the FULL canvas, alpha crop is measure-only — transparent web margins reveal the webcam again"

This reverts commit 0f441d825a.

MyMistakes.md

@@ -15,40 +15,7 @@
 
 ## 🔬 Recipes registry
 
-### Web-overlay transparency: measure with the alpha crop, COMPOSE with the full canvas
-
-(2026-09-05, take-19-2/take-20 — "the webcam is a black square under the web widget".
-
-**Symptom:** WebView2-based web overlays (StreamElements alert hosts etc.) rendered
-with hard opaque boxes over the webcam in the RECORDING but the preview looked fine,
-and the FIRST take after a rebuild was good but later takes went opaque — a
-stateful-looking bug.
-
-**Root cause:** the capture was alpha-CROPPED to the widget's content bounding box
-(`FindContentBounds` — every non-zero-alpha pixel) and that CROP was handed to the
-compositor, which `UniformToFill`-scales a source into the element rect. A crop has
-NO transparent margins by construction, so the composite zoomed the opaque content
-to cover the ENTIRE element rect (hard box!) whenever the widget drew anything. It
-looked stateful because an idle/transparent page yields a full-frame crop ≈ the
-correct full-canvas viewport (good), while any real content yields a tight crop +
-zoom (bad).
-
-**The rule (OBS browser-source model):** the page is a FIXED canvas (1920×1080 here);
-the element rect is a VIEWPORT onto it. Measure/select with the alpha crop; hand the
-composite the FULL canvas with its transparent background intact — `UniformToFill`
-then maps the page region 1:1 into the element rect and the page's transparent
-margins reveal the layers beneath (the webcam). When feeding a compositor that
-scales sources to fill a rect, NEVER feed it a crop of your source unless the rect
-is meant to re-frame it.
-
-Recipe:
-1. Keep `FindContentBounds` for the preview bitmap / selection bounding box.
-2. Feed the compositor a full-canvas frame whose background is alpha 0, from an
-   8-deep ring (same identity/Epoch discipline as every producer — a single reused
-   scratch array tears under the consumer).
-3. Pin the reveal contract with a compositor test: full-canvas transparent-margin
-   frame over a webcam rect → margin pixel = webcam color, opaque badge pixel =
-   widget color.
+### Shrink / re-encode an image for the README (screenshots → small hero image)
 
 Worked out 2026-08-29 (the recipe was NEVER recorded the first time it was done, so
 it had to be re-derived from scratch — that's the incident this entry exists to end).