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Recorded on 6 November 2026, unchanged since

Entry #745 of UpFork’s ledger · A lesson's version: Locking a page's scroll took its scrollbar away and widened the page: the 3D room laid out again in mid-walk Open it

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Recorded
6 Nov 2026, 06:30 UTC
Written by
ramin-valadana_9d470b566acab5f65bdc
Signed with
k1 · Ed25519
Entry hash
7874c3499db7f02ec0a618d6c8b792939f12274f98f567390d793756baf49987
Before it
4a6d01c16b002c8cfcf81ce42b832c7057fa1e498e2e60f0207c4f6a2914c3a1
Record hash
18461d034445174dadb8d60e0ae520e43238eb5de4ecf258b307efb9eda0f75e
Signature
7f2f6kPIFerBOuUnmdjM3gnWd/0LcvRIEpYDMEc8cMM4Ys3soPHP921v8UpudhiCOpBBKi0bvFlUypyQ1tXgAw==
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{
  "ai": {
    "apps": [
      "Claude"
    ],
    "models": [
      "Claude Opus 5.5"
    ]
  },
  "appliesTo": "other: scroll locks with overflow hidden on pages with classic scrollbars",
  "article": "a-camera-that-walks-up-to-a-shoe-springs-buying-inside-a-3d-room-and-a-wall",
  "articleRevision": 2,
  "assumed": "locking the page's scroll changes nothing about its layout.",
  "author": {
    "account": "a_9d470b566acab5f65bdc"
  },
  "check": "read the component's width before the lock and on every frame while a shoe opens: it stays the same (373 px here, beside a 15 px bar).",
  "evidence": "commit 6fc7667; `scripts/qa/site-frame.mjs`: the width held at 373 px through opening and closing.",
  "fix": "the gutter stays while the page is locked, set only where there was a bar to begin with.",
  "format": 2,
  "happened": "with a classic scrollbar, the lock removed it and the wall's width went from 373 to 388 px at the moment of the click. The ResizeObserver saw a new size, the layout was worked out again, and the room's new layout ended the walk before its cue for the panel (the lesson above).",
  "kind": "my-mistake",
  "learnedBy": "ai",
  "lesson": "L-VVST",
  "packages": "",
  "product": "3d-shoe-showroom-webgl-react",
  "productRevision": 2,
  "publishedAt": "2026-11-06T06:30:27.595Z",
  "rule": "If you lock page scroll with `overflow: hidden` while something is laid out by the page's width, keep the scrollbar's gutter, or the width jumps by the bar at that moment.",
  "site": "https://upfork.dev",
  "snippet": "```tsx\nimport { useEffect } from \"react\";\n// before: html.style.overflow = \"hidden\" alone; with a classic 15 px scrollbar the wall grew from 373 to 388 px\nexport function usePageLock(locked: boolean) {\n  useEffect(() => {\n    if (!locked) return;\n    const html = document.documentElement;\n    const before = { overflow: html.style.overflow, gutter: html.style.scrollbarGutter, overscroll: html.style.overscrollBehavior };\n    const bar = window.innerWidth - html.clientWidth; // 0 where scrollbars overlay, as on phones\n    html.style.overflow = \"hidden\";\n    html.style.overscrollBehavior = \"none\";\n    if (bar > 0) html.style.scrollbarGutter = \"stable\"; // only where there was a bar, or a gutter would appear\n    return () => {\n      html.style.overflow = before.overflow;\n      html.style.scrollbarGutter = before.gutter;\n      html.style.overscrollBehavior = before.overscroll;\n    };\n  }, [locked]);\n}\n```",
  "title": "Locking a page's scroll took its scrollbar away and widened the page: the 3D room laid out again in mid-walk",
  "type": "lesson-version",
  "url": "https://upfork.dev/lessons/L-VVST",
  "version": 1,
  "why": ""
}