[Fizz] Model SuspenseList with tail="hidden" and tail="collapsed" as virtual boundaries

packages/react-dom-bindings/src/server/ReactFizzConfigDOM.js

@@ -4573,6 +4573,24 @@ export function pushEndActivityBoundary(
   target.push(endActivityBoundary);
 }
 
+// SuspenseList with hidden tails are encoded as comments.
+const startSuspenseListBoundary = stringToPrecomputedChunk('<!--~-->');
+const endSuspenseListBoundary = stringToPrecomputedChunk('<!--/~-->');
+
+export function pushStartSuspenseListBoundary(
+  target: Array<Chunk | PrecomputedChunk>,
+  renderState: RenderState,
+): void {
+  target.push(startSuspenseListBoundary);
+}
+
+export function pushEndSuspenseListBoundary(
+  target: Array<Chunk | PrecomputedChunk>,
+  renderState: RenderState,
+): void {
+  target.push(endSuspenseListBoundary);
+}
+
 // Suspense boundaries are encoded as comments.
 const startCompletedSuspenseBoundary = stringToPrecomputedChunk('<!--$-->');
 const startPendingSuspenseBoundary1 = stringToPrecomputedChunk(

packages/react-dom-bindings/src/server/ReactFizzConfigDOMLegacy.js

@@ -24,6 +24,8 @@ import {
   pushSegmentFinale as pushSegmentFinaleImpl,
   pushStartActivityBoundary as pushStartActivityBoundaryImpl,
   pushEndActivityBoundary as pushEndActivityBoundaryImpl,
+  pushStartSuspenseListBoundary as pushStartSuspenseListBoundaryImpl,
+  pushEndSuspenseListBoundary as pushEndSuspenseListBoundaryImpl,
   writeStartCompletedSuspenseBoundary as writeStartCompletedSuspenseBoundaryImpl,
   writeStartClientRenderedSuspenseBoundary as writeStartClientRenderedSuspenseBoundaryImpl,
   writeEndCompletedSuspenseBoundary as writeEndCompletedSuspenseBoundaryImpl,
@@ -259,6 +261,28 @@ export function pushEndActivityBoundary(
   pushEndActivityBoundaryImpl(target, renderState);
 }
 
+export function pushStartSuspenseListBoundary(
+  target: Array<Chunk | PrecomputedChunk>,
+  renderState: RenderState,
+): void {
+  if (renderState.generateStaticMarkup) {
+    // A completed boundary is done and doesn't need a representation in the HTML
+    // if we're not going to be hydrating it.
+    return;
+  }
+  pushStartSuspenseListBoundaryImpl(target, renderState);
+}
+
+export function pushEndSuspenseListBoundary(
+  target: Array<Chunk | PrecomputedChunk>,
+  renderState: RenderState,
+): void {
+  if (renderState.generateStaticMarkup) {
+    return;
+  }
+  pushEndSuspenseListBoundaryImpl(target, renderState);
+}
+
 export function writeStartCompletedSuspenseBoundary(
   destination: Destination,
   renderState: RenderState,