test(web): cover streamed fallbacks with dynamic text holes in parity harness

Regression scenario for solid#2877 (fixed in dom-expressions#542): a Loading
fallback containing dynamic text holes serializes with comment separators
inside the swap range, so $df must scan to its own matching pl marker instead
of stopping at the first comment.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: ryansolid

packages/solid-web/test/harness/__artifacts__/dynamic-fallback-stream.json

@@ -0,0 +1,5 @@
+{
+  "name": "dynamic-fallback-stream",
+  "shell": "<div _hk=1><span>status </span><!--$--><template id=\"pl-2\"></template>preparing <!--!$-->42<!--!$-->% done<!--pl-2--><!--/--></div><script>(self.$R=self.$R||{})[\"\"]=[];_$HY.r[\"0\"]=$R[0]=($R[1]=($R[2]=() => {\n  const resolver = {\n    p: 0,\n    s: 0,\n    f: 0\n  };\n  resolver.p = new Promise((resolve, reject) => {\n    resolver.s = resolve;\n    resolver.f = reject;\n  });\n  return resolver;\n})()).p;_$HY.r[\"2_fr\"]=$R[3]=($R[4]=$R[2]()).p;</script>",
+  "rest": "<template id=\"2\"><strong _hk=2000>ready</strong></template><script>($R[5]=(resolver, data) => {\n  resolver.s(data);\n  resolver.p.s = 1;\n  resolver.p.v = data;\n})($R[1],\"ready\");$df(\"2\");function $df(e,n,o,t){if(!(n=document.getElementById(e)))return 0;if(!(o=document.getElementById(\"pl-\"+e)))return(_$HY.dq=_$HY.dq||{})[e]=1,0;for(;o&&(8!==o.nodeType||o.nodeValue!==\"pl-\"+e);)t=o.nextSibling,o.remove(),o=t;_$HY.done?o.remove():o.replaceWith(n.content),n.remove(),_$HY.fe(e),$dfd();return 1}function $dfl(e,o,n){if(!(o=document.getElementById(\"pl-\"+e)))return(_$HY.dlq=_$HY.dlq||{})[e]=1,0;if(o._$fl)return 1;for(n=o.nextSibling;n;){if(8===n.nodeType&&n.nodeValue===\"pl-\"+e){o.parentNode&&o.parentNode.insertBefore(o.content.cloneNode(!0),n),o._$fl=1,$dfd();return 1}n=n.nextSibling}return 0}function $dflj(e,i){for(i=0;i<e.length;i++)$dfl(e[i])}function $dfd(e,i){if(e=_$HY.dq){_$HY.dq=0;for(i in e)$df(i)}if(e=_$HY.dlq){_$HY.dlq=0;for(i in e)$dfl(i)}}function $dfs(e,c,d){(_$HY.sc=_$HY.sc||{})[e]=c,d&&((_$HY.sd=_$HY.sd||{})[e]=1)}function $dfg(e,g,i,k){if(!(g=_$HY.sg&&_$HY.sg[e]))return;for(i=0;i<g.length;i++)if(_$HY.sc&&_$HY.sc[g[i]]>0)return;for(i=0;i<g.length;i++)k=g[i],delete _$HY.sg[k],$df(k)}function $dfc(e){if(--_$HY.sc[e]<=0){delete _$HY.sc[e],_$HY.sg&&_$HY.sg[e]?$dfg(e):!(_$HY.sd&&_$HY.sd[e])&&$df(e);_$HY.sd&&delete _$HY.sd[e]}}function $dfj(e,i,n){for(i=0;i<e.length;i++)if(_$HY.sc&&_$HY.sc[e[i]]>0){for(n=0;n<e.length;n++)(_$HY.sg=_$HY.sg||{})[e[n]]=e;return}for(i=0;i<e.length;i++)$df(e[i])};$R[5]($R[4],!0);</script>"
+}

packages/solid-web/test/harness/scenarios.tsx

@@ -371,6 +371,33 @@ function FalsyAndProp() {
   return <ValueCard value={val() && val()!.toUpperCase()} />;
 }
 
+// ---------------------------------------------------------------------------
+// Streamed boundary whose FALLBACK contains dynamic text holes (#2877,
+// dom-expressions#542). The fallback serializes with <!--!$--> separator
+// comments inside the swap range, so $df's removal walk must stop only at its
+// own matching <!--pl-X--> end marker — a scan that halts at the first comment
+// of any kind deletes just the pre-separator slice and leaves the rest of the
+// fallback in the DOM as permanent debris ("ready42% done").
+let refreshDynamicFallback!: () => void;
+function DynamicFallbackStream() {
+  const [version, setVersion] = createSignal(0);
+  refreshDynamicFallback = () => setVersion(v => v + 1);
+  const [progress] = createSignal(42);
+  const report = createMemo(async () => {
+    const v = version();
+    await sleep(10);
+    return v ? `ready-${v}` : "ready";
+  });
+  return (
+    <div>
+      <span>status </span>
+      <Loading fallback={<>preparing {progress()}% done</>}>
+        <strong>{report()}</strong>
+      </Loading>
+    </div>
+  );
+}
+
 // ---------------------------------------------------------------------------
 // Portal: client-only island (#2876). Server renders nothing for the portal;
 // the client renders its children fresh once hydration settles. Mounting into
@@ -629,6 +656,16 @@ export const scenarios: Scenario[] = [
     expectedTextAfterUpdate: "set:HI",
     stableSelector: "div"
   },
+  {
+    name: "dynamic-fallback-stream",
+    App: DynamicFallbackStream,
+    async: true,
+    expectedText: "status ready",
+    serverText: "status preparing 42% done",
+    update: () => refreshDynamicFallback(),
+    expectedTextAfterUpdate: "status ready-1",
+    stableSelector: "div, span"
+  },
   {
     name: "portal-client-island",
     App: PortalClientIsland,