Should the page-wide WebGL/scene options be one selectable background effect instead of a raw toggle + code fields?

The question: The page-wide Custom WebGL Background shipped as an on/off switch plus two code editors (Scene DOM and Scene code (JS)) sitting in Page Settings → Animations. It renders a three.js scene behind the whole page. Should all of that instead be one selectable effect in the Animation Engine — for pages only?

Context. We had just built the page-scene capability to clone an art-directed landing (a live three.js temple carried behind the content, bound to page scroll). The controls ended up as: the page-wide Background Effect picker (37 curated tiles), a fixed-behind-content toggle, and — separately — the Custom WebGL Background switch + Scene DOM + Scene code. Conceptually these are all "what renders behind the whole page," but the WebGL cluster read as three unrelated advanced fields, and a bare toggle is not how the rest of the engine presents its effects (you pick an effect from tiles).

Options considered.

• Leave it as a switch + two code fields. Works, but undiscoverable and inconsistent — it doesn't feel like "an effect you choose," and the two code editors are always visible even when off.
• Add a custom_webgl tile to the shared Background picker (bg_effect). Tempting for unification, but that picker is multi-instance / stackable (petals + rain + fog…). A WebGL scene is singular — you never want twelve of them — so folding it into a stackable per-slot picker is a category mismatch, and it would also surface on the per-element/section Background card, where a full-viewport scene makes no sense.
• A dedicated single-choice picker: None / Custom (WebGL scene). A multi-picker whose tiles are None and Custom (WebGL scene); choosing Custom reveals the Scene DOM + Scene code editors. Page-only.

Decision. The third option. The page WebGL background is now a selectable tile — page_webgl with a mode picker (none / custom) — and the code editors live under the Custom tile's reveal. The standalone enable switch is gone (selecting the tile is the enable). It is injected only into the page picker, never the per-element/section Background card, and stays admin-gated (unfiltered_html). This is the exact pattern the Preloader already uses (a Custom (code) style alongside the built-in styles).

Why.

• A picker tile makes it first-class and discoverable — "here is where I choose my page background, and Custom lets me paste a scene" — instead of an advanced switch a builder scrolls past.
• Singular, not stackable. Keeping it out of the multi-instance bg_effect card respects that a full-viewport scene is one thing, not a layer in a stack, and keeps the per-element picker clean.
• Raw code stays clearly distinct from curated effects. The 37 built-in backgrounds are safe, editable (color/speed pickers); a WebGL scene is admin-authored code — a black box. Its own tile that reveals code editors is honest about that difference while still living in the same "pick a background" control.
• Consistency with the Preloader Custom style means one mental model for "built-in options, plus a Custom code escape hatch," applied the same way across the engine.
• Extensible. The picker can later gain curated scene presets as additional tiles without changing the shape.

Status: Accepted. The render path and the upw:scroll hook are unchanged; only the option packaging moved.