feat: store email attachments in R2 and expose as RSS enclosures

Attachments from incoming emails are uploaded to an optional Cloudflare R2
bucket and exposed as <enclosure> elements in RSS and <link rel="enclosure">
in Atom feeds, served at /files/{id}/{filename} with immutable caching.

R2 is opt-in: if ATTACHMENT_BUCKET is not bound the feature is a no-op.
Attachments are cleaned up from R2 on email/feed deletion and during
size-based feed trimming. Adds MockR2 to the test setup.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/lib/forwardemail.ts

@@ -1,6 +1,16 @@
 import { EmailParser } from "../utils/email-parser";
 import { Env } from "../types";
-import { processEmail } from "./email-processor";
+import { processEmail, RawAttachment } from "./email-processor";
+
+export interface ForwardEmailAttachment {
+  filename?: string;
+  contentType?: string;
+  size?: number;
+  content?:
+    | { type: "Buffer"; data: number[] }
+    | ArrayBuffer
+    | ArrayBufferView;
+}
 
 export interface ForwardEmailPayload {
   recipients?: string[];
@@ -17,7 +27,7 @@ export interface ForwardEmailPayload {
   headerLines?: Array<{ key: string; line: string }>;
   headers?: string;
   raw?: string;
-  attachments?: Array<any>;
+  attachments?: ForwardEmailAttachment[];
 }
 
 function normalizeEmail(value: string): string {
@@ -41,12 +51,36 @@ function extractSenderAddresses(payload: ForwardEmailPayload): string[] {
   return Array.from(new Set(matches.map(normalizeEmail)));
 }
 
+function toArrayBuffer(
+  content: ForwardEmailAttachment["content"],
+): ArrayBuffer | null {
+  if (!content) return null;
+  if (content instanceof ArrayBuffer) return content;
+  if (ArrayBuffer.isView(content)) return (content as ArrayBufferView).buffer as ArrayBuffer;
+  if (typeof content === "object" && content.type === "Buffer" && Array.isArray(content.data)) {
+    return Uint8Array.from(content.data).buffer as ArrayBuffer;
+  }
+  return null;
+}
+
 export async function handleForwardEmail(
   payload: ForwardEmailPayload,
   env: Env,
 ): Promise<Response> {
   const emailData = EmailParser.parseForwardEmailPayload(payload);
 
+  const rawAttachments: RawAttachment[] = (payload.attachments ?? [])
+    .map((a) => {
+      const buffer = toArrayBuffer(a.content);
+      if (!buffer) return null;
+      return {
+        filename: a.filename || "attachment",
+        contentType: a.contentType || "application/octet-stream",
+        content: buffer,
+      };
+    })
+    .filter((a): a is RawAttachment => a !== null);
+
   return processEmail(
     {
       toAddress: payload.recipients?.[0] || "",
@@ -56,6 +90,7 @@ export async function handleForwardEmail(
       content: emailData.content,
       receivedAt: emailData.receivedAt,
       headers: emailData.headers,
+      attachments: rawAttachments,
     },
     env,
   );