fix(script): honor async false for client scripts

packages/vinext/src/shims/script.tsx

@@ -99,11 +99,41 @@ function buildBeforeInteractiveScriptProps(options: {
   return scriptProps;
 }
 
+function setBooleanScriptAttribute(el: HTMLScriptElement, attr: string, value: unknown): boolean {
+  const enabled = value !== false && value !== "false" && Boolean(value);
+
+  switch (attr) {
+    case "async":
+      el.async = enabled;
+      break;
+    case "defer":
+      el.defer = enabled;
+      break;
+    case "noModule":
+    case "nomodule":
+      el.noModule = enabled;
+      break;
+    default:
+      return false;
+  }
+
+  if (!enabled) {
+    // Dynamic script elements start in the browser's force-async state.
+    // Setting and removing the attribute mirrors Next.js and clears that state.
+    el.setAttribute(attr, "");
+    el.removeAttribute(attr);
+  }
+
+  return true;
+}
+
 function setScriptAttributes(el: HTMLScriptElement, rest: Record<string, unknown>): void {
   for (const [attr, value] of Object.entries(rest)) {
     if (attr === "dangerouslySetInnerHTML") continue;
-    if (attr === "className") {
-      el.setAttribute("class", String(value));
+    if (value === undefined) continue;
+    if (setBooleanScriptAttribute(el, attr, value)) continue;
+    if (attr === "className" && typeof value === "string") {
+      el.setAttribute("class", value);
     } else if (typeof value === "string") {
       el.setAttribute(attr, value);
     } else if (typeof value === "boolean" && value) {

tests/script.test.ts

@@ -198,4 +198,58 @@ describe("Script SSR rendering", () => {
     expect(appendedScripts).toHaveLength(1);
     expect(appendedScripts[0]!.attrs.nonce).toBe("property-nonce");
   });
+
+  it("clears forced async execution when async is explicitly false", () => {
+    type MockScript = {
+      async: boolean;
+      attrs: Record<string, string>;
+      src: string;
+      setAttribute(name: string, value: string): void;
+      removeAttribute(name: string): void;
+      getAttribute(name: string): string | null;
+      addEventListener(): void;
+    };
+
+    const appendedScripts: MockScript[] = [];
+    class MockHTMLElement {}
+
+    const createdScript: MockScript = {
+      async: true,
+      attrs: {},
+      src: "",
+      setAttribute(name: string, value: string) {
+        this.attrs[name] = value;
+      },
+      removeAttribute(name: string) {
+        Reflect.deleteProperty(this.attrs, name);
+      },
+      getAttribute(name: string): string | null {
+        return this.attrs[name] ?? null;
+      },
+      addEventListener() {},
+    };
+
+    setGlobalValue("HTMLElement", MockHTMLElement);
+    setGlobalValue("window", {});
+    setGlobalValue("document", {
+      querySelector() {
+        return null;
+      },
+      createElement(tagName: string) {
+        expect(tagName).toBe("script");
+        return createdScript;
+      },
+      body: {
+        appendChild(element: unknown) {
+          appendedScripts.push(element as typeof createdScript);
+        },
+      },
+    });
+
+    handleClientScriptLoad({ src: "/ordered-script.js", async: false });
+
+    expect(appendedScripts).toHaveLength(1);
+    expect(appendedScripts[0]!.async).toBe(false);
+    expect(appendedScripts[0]!.attrs).not.toHaveProperty("async");
+  });
 });