From 18a42a878c24199be071ba0fe3fea7317aa3d065 Mon Sep 17 00:00:00 2001
From: Adam Daley <admdly@users.noreply.github.com>
Date: Thu, 17 Sep 2026 15:06:25 +0100
Subject: [PATCH] Fix Illegal invocation in moderation emails

---
 src/services/extensions/v2/email/mxroute.ts | 17 ++++---
 src/services/extensions/v2/email/resend.ts  | 17 ++++---
 src/services/extensions/v2/email/types.ts   |  6 +++
 test/services/extensions/v2/email.test.ts   | 56 +++++++++++++++++++++
 4 files changed, 80 insertions(+), 16 deletions(-)

diff --git a/src/services/extensions/v2/email/mxroute.ts b/src/services/extensions/v2/email/mxroute.ts
index cdecadb..c212d7d 100644
--- a/src/services/extensions/v2/email/mxroute.ts
+++ b/src/services/extensions/v2/email/mxroute.ts
@@ -1,10 +1,11 @@
-import type {
-  EmailIdentity,
-  EmailMessage,
-  EmailSender,
-  EmailSendResult,
-  EnvReader,
-  FetchFn
+import {
+  defaultFetch,
+  type EmailIdentity,
+  type EmailMessage,
+  type EmailSender,
+  type EmailSendResult,
+  type EnvReader,
+  type FetchFn
 } from "./types";
 
 const SMTP_API_URL = "https://smtpapi.mxroute.com/";
@@ -33,7 +34,7 @@ export function loadMxrouteConfig(
 export class MxrouteSender implements EmailSender {
   constructor(
     private config: MxrouteConfig,
-    private fetchFn: FetchFn = globalThis.fetch
+    private fetchFn: FetchFn = defaultFetch
   ) {}
 
   async send(message: EmailMessage): Promise<EmailSendResult> {
diff --git a/src/services/extensions/v2/email/resend.ts b/src/services/extensions/v2/email/resend.ts
index 533376f..e67a6d4 100644
--- a/src/services/extensions/v2/email/resend.ts
+++ b/src/services/extensions/v2/email/resend.ts
@@ -1,10 +1,11 @@
-import type {
-  EmailIdentity,
-  EmailMessage,
-  EmailSender,
-  EmailSendResult,
-  EnvReader,
-  FetchFn
+import {
+  defaultFetch,
+  type EmailIdentity,
+  type EmailMessage,
+  type EmailSender,
+  type EmailSendResult,
+  type EnvReader,
+  type FetchFn
 } from "./types";
 
 const RESEND_API_URL = "https://api.resend.com/emails";
@@ -29,7 +30,7 @@ export function loadResendConfig(
 export class ResendSender implements EmailSender {
   constructor(
     private config: ResendConfig,
-    private fetchFn: FetchFn = globalThis.fetch
+    private fetchFn: FetchFn = defaultFetch
   ) {}
 
   async send(message: EmailMessage): Promise<EmailSendResult> {
diff --git a/src/services/extensions/v2/email/types.ts b/src/services/extensions/v2/email/types.ts
index 8db1105..0e16130 100644
--- a/src/services/extensions/v2/email/types.ts
+++ b/src/services/extensions/v2/email/types.ts
@@ -13,6 +13,12 @@ export interface EmailSender {
 
 export type FetchFn = typeof globalThis.fetch;
 
+// Workers' fetch requires its `this` receiver: storing `globalThis.fetch`
+// as a bare reference and calling it later throws "Illegal invocation".
+// Keep the lookup behind an arrow so the default sender always calls it
+// bound.
+export const defaultFetch: FetchFn = (...args) => globalThis.fetch(...args);
+
 // Minimal env surface the email subsystem needs. Shaped to match
 // PlatformContext, so routes pass getPlatform(c) directly — the same way
 // GITHUB_TOKEN and the assertion secrets are read everywhere else.
diff --git a/test/services/extensions/v2/email.test.ts b/test/services/extensions/v2/email.test.ts
index b7b6442..306a9d9 100644
--- a/test/services/extensions/v2/email.test.ts
+++ b/test/services/extensions/v2/email.test.ts
@@ -258,6 +258,62 @@ describe("factory", () => {
   });
 });
 
+describe("default fetch binding", () => {
+  it("sends through globalThis.fetch without an Illegal invocation error", async () => {
+    // Workers throws "Illegal invocation" for a detached fetch while Node
+    // tolerates it: enforce the Workers behaviour so the default stays bound.
+    const originalFetch = globalThis.fetch;
+    const urls: string[] = [];
+    function workersLikeFetch(
+      this: unknown,
+      input: string | URL | Request,
+      _init?: RequestInit
+    ): Promise<Response> {
+      if (this !== globalThis) {
+        throw new TypeError(
+          "Illegal invocation: function called with incorrect `this` reference."
+        );
+      }
+      urls.push(String(input));
+      return Promise.resolve(jsonResponse({ success: true, message: "sent" }));
+    }
+
+    globalThis.fetch = workersLikeFetch as typeof fetch;
+    try {
+      const message = {
+        to: "author@example.com",
+        subject: "s",
+        html: "<p>hi</p>",
+        text: "hi"
+      };
+      const mxrouteConfig = loadMxrouteConfig(reader(MXROUTE_VARS), IDENTITY)!;
+      await expect(
+        new MxrouteSender(mxrouteConfig).send(message)
+      ).resolves.toEqual({ ok: true });
+
+      const resendConfig = loadResendConfig(
+        reader({ EXTENSIONS_V2_RESEND_API_KEY: "re_key" }),
+        IDENTITY
+      )!;
+      await expect(
+        new ResendSender(resendConfig).send(message)
+      ).resolves.toEqual({ ok: true });
+
+      // notify.ts calls createEmailSender(env) with no injected fetch.
+      const viaFactory = createEmailSender(reader(MXROUTE_VARS));
+      await expect(viaFactory.send(message)).resolves.toEqual({ ok: true });
+
+      expect(urls).toEqual([
+        "https://smtpapi.mxroute.com/",
+        "https://api.resend.com/emails",
+        "https://smtpapi.mxroute.com/"
+      ]);
+    } finally {
+      globalThis.fetch = originalFetch;
+    }
+  });
+});
+
 describe("moderation templates", () => {
   it("includes the reason and escapes markup", () => {
     const message = buildModerationEmail({