feedback7 R22-RENDER: closed eyes stay closed without the stencil masks — the eyelid clips' covered slots hide when their centre leaves the clip polygon (GitHub #177, re-implemented from PR #384 by @Convey123); golden: unchanged

The eyelids of 佩佩, 仇白, 隐德来希, 琳琅诗怀雅 and other models are Spine clipping attachments: the polygon is the eye's
opening and the eyeball / eye-white meshes drawn after it are clipped to it, so a blink or a knock-down closes the eye
through the mask. render/app.js pickClipping keeps the masks only for a lone clipped skeleton at high quality, so in a
battle the eyeballs showed through the closed lids. SpineActor._eyeMaskFallback now runs after each update while the
masks are off: it walks the draw order like pixi-spine (from a slot whose attachment in force is a clip, to its
endSlot — any skin) and hides the slot container of a covered slot whose drawn centre (a mesh's mean vertex, a region's
quad centre) lies outside the clip polygon [ASSUMED: all or nothing per slot]; turning the masks on shows them again.

PR #384's version hid `slot.currentSprite`, which pixi-spine leaves null on a mesh slot — every covered slot of the
417 local operator skeletons' 73 clipped ones is a mesh (313) or a region (54; regions have no worldVerticesLength, so
it never measured them) — and its test stubbed a currentSprite onto every slot, so nothing was hidden in the game. Kept
from it: the diagnosis, the ray-casting pointInPolygon and the key-frame expectations.

Tests: test/render/eyemask.test.js (new, 7, on real runtime objects — the official skeletons in @pixi-spine/runtime-3.8's
real Spine, @pixi/core display objects with a 16 px canvas stand-in, the real SpineActor: the eyeballs are meshes in
the clip's container; 佩佩 / 仇白 Die and 隐德来希 / 琳琅诗怀雅 Idle hide exactly the eye slots in the closed frames and
nothing open; a 30 Hz sweep of six clips; masks on hide nothing, turning them on shows all) 7/7 — the five skeleton tests
skip without public/assets (not committed; npm run assets), and fail on PR #384's code; render unitview, enemy attack
clips, texas skill clip 45/45.

public/js/render/app.js

@@ -1569,8 +1569,9 @@ export async function createFieldView(host, options = {}) {
   // Crowded fields render skeletons through staggered RenderTexture impostors (units.js): the interval grows with
   // the number of Spine units so the per-frame vertex work stays roughly constant (hysteresis: re-evaluated
   // every 30 frames). Prep and ordinary fields keep full-rate direct rendering.
-  // Spine clipping masks (only eyeball clips on the current roster, invisible at chibi scale) each cost a stencil
-  // render-pass break (~2–5 ms of GPU on tiled GPUs): kept only for a lone clipped skeleton at high quality
+  // Spine clipping masks (the eyelids on the current roster) each cost a stencil render-pass break (~2–5 ms of GPU on
+  // tiled GPUs): kept only for a lone clipped skeleton at high quality; without them SpineActor hides the eyeball slots a
+  // closed lid would cut (GitHub #177, spine.js _eyeMaskFallback)
   let clipAllowed = true;
   function pickClipping() {
     let n = 0;