Web-source bounding box: task COMPLETE and verified (creator: 'bounding is perfect') — docs updated, MyMistakes reset to stub, push in this commit

Root-cause note: the apparent remaining gap was a WIDGET GLOW EFFECT (the widget's own CSS glow pushed
out its perceived borders), not a code bug — the alpha-bbox already hugged the glow halo. Verified
perfect with a second widget without the effect.

MyMistakes.md

@@ -2,46 +2,4 @@
 
 > One task at a time. Updated before every commit touching that task: current iteration +
 > why the last one failed. On task complete, committed AND pushed → truncate to this stub.
-> A new task does NOT seed this file until its first failure.
-
-## Task (active — committed `582d1f4`, NOT pushed, awaiting creator verification)
-Stream widget bounding box: hug the widget on all four sides, pinned to canvas (0,0).
-
-## Iterations that failed
-1. **e917c41 — fixed 1920×1080 viewport + `Stretch="Uniform"` + startup registration.**
-   Failed: `Uniform` letterboxed the 16:9 canvas into arbitrary‑sized boxes → asymmetric dead
-   padding read as a "gap". Lesson: Fill the box with the cropped frame, never Uniform.
-2. **9d4103c — per‑document CSS reset (`html/body` width/height 100%) + (0,0) anchor.**
-   Failed ("enlarged the gap"): forcing dimensions overrode the widget's own layout and expanded
-   the dead space. Lesson: inject only `overflow:hidden` + transparent background — never set sizes.
-3. **8d793af — viewport == element‑box size + `Stretch="Fill"`.**
-   Failed (janky / truncating / scrollbars): hosting at the box size clips full‑bleed widgets to
-   their upper‑left chunk, and tracking the box reflows the page on drag. Lesson: render at a
-   fixed canvas size, never track the box.
-4. **f39ebd9 — crop capture to `scrollWidth/scrollHeight` bounds + (0,0) + Fill.**
-   Partially passed (panel fixes 1a/1b/4 confirmed) but the box stayed loose; the apparent
-   "tight right/bottom" was just the small‑viewport clip edge. **ROOT CAUSE: the crop never ran.**
-   The script returned `JSON.stringify(...)` (a string); `ExecuteScriptAsync` JSON‑encodes every
-   result, so the JSON was double‑encoded → `JsonDocument.Parse` got a string node →
-   `GetProperty` threw → try/catch swallowed → bounds unset → no crop. Lesson: return a real JS
-   object, never a stringified one. Also: scroll extents ≠ widget rect (they include page margins).
-5. **70fe2b8 — fixed canvas‑size viewport (1920×1080) + crop + Fill.**
-   Image render/resize became solid (creator confirmed) but the box still gapped right/bottom and
-   wasn't 0,0. Same silent JSON bug — the crop still never executed — and the measure was scroll
-   extents regardless. Lesson: verify declared mechanics actually execute; assume nothing ran.
-
-## Current iteration (web bounding box — UNCOMMITTED, verification pending)
-ALPHA-BBOX CROP: `FindContentBounds` scans the captured Bgra32 frame and returns the bounding box
-of non-transparent pixels (the background is injected transparent, so alpha = the widget's extent).
-Capture is cropped to that rect and `Stretch="Fill"` maps it flush under the box. No DOM query, no
-layout timing — the crop rect IS the rendered widget by construction, so it can NEVER truncate
-visible content. Worst case (widget fills the canvas) = full frame = the confirmed-good render.
-Canvas-size viewport + Fill untouched. `QueryContentBoundsAsync` + the JS script are DELETED.
-
-## Iteration that just failed (`a5b9952` — wrapper-excluded DOM-union crop + image alignment)
-Broke the image rendering — creator could not evaluate the box because the image was gone/ruined.
-Why: the visible-element-union rect is measured ONCE on NavigationCompleted; widget layout isn't
-settled then (async fonts/images, load animations, iframes), so the crop rect comes out tiny/wrong
-and the Fill-stretched frame renders a broken/zoomed sliver. This was against the creator's explicit
-"don't break the rendering" instruction. Lesson: measure actual RENDERED PIXELS (alpha), never
-transient DOM state; and never ship a crop blind.
+> A new task does NOT seed this file until its first failure.