fix: close durable queue and runtime gaps

packages/mail/test/mail.test.ts

@@ -1,5 +1,5 @@
 import { expect, test } from "bun:test";
-import { defineMail, defineMailTemplate } from "../src/index.ts";
+import { defineMail, defineMailTemplate, sealedMailDriver } from "../src/index.ts";
 
 test("mail templates render and sandbox blocks accidental recipients", async () => {
   const sent: unknown[] = [];
@@ -16,3 +16,32 @@ test("mail templates render and sandbox blocks accidental recipients", async ()
   expect(sent).toHaveLength(1);
   await expect(mail.send({ to: "real@example.com", subject: "no" })).rejects.toThrow("SANDBOX");
 });
+
+test("sealed drivers decrypt lazily once and delegate send/test", async () => {
+  let opens = 0;
+  const sent: string[] = [];
+  const driver = sealedMailDriver({
+    sealedCredential: "ciphertext",
+    async unseal(value) {
+      opens++;
+      expect(value).toBe("ciphertext");
+      return "plaintext-secret";
+    },
+    create(credential) {
+      expect(credential).toBe("plaintext-secret");
+      return {
+        async send(message) {
+          sent.push(message.subject);
+        },
+        async test() {
+          return { ok: true };
+        },
+      };
+    },
+  });
+  expect(opens).toBe(0);
+  await driver.send({ to: "safe@example.test", subject: "one" });
+  expect(await driver.test?.()).toEqual({ ok: true });
+  expect(opens).toBe(1);
+  expect(sent).toEqual(["one"]);
+});