fix(email-renderer): preserve fallbacks when AMP validation is unavailable

packages/email-renderer/test/email.test.ts

@@ -57,6 +57,17 @@ const document: BlockDocument = {
 };
 
 describe("email renderer", () => {
+  test("optional AMP validation failures preserve HTML/text fallbacks", async () => {
+    for (const ampValidator of [async () => {throw new Error("network unavailable")}, () => new Promise<never>(() => {})]) {
+      const result=await renderEmail(document,{amp:true,ampValidator,ampValidationTimeoutMs:10});
+      expect(result.ok).toBe(true);
+      if(!result.ok)continue;
+      expect(result.value.parts.amp).toBeUndefined();
+      expect(result.value.parts.html.content).toContain("Hello &lt;world&gt;");
+      expect(result.value.parts.text.content).toContain("Hello <world>");
+      expect(result.value.warnings.some(item=>item.code==="amp.validatorUnavailable"&&item.severity==="warning")).toBe(true);
+    }
+  });
   test("builder column rows export without nesting mj-column inside mj-column", async () => {
     for (const count of [1,2,3,4]) {
       const draft=structuredClone(document);