feat(email): accept custom message headers in sendRaw (#3411)

* feat(email): accept custom message headers in sendRaw

Lets callers set transport-level headers such as List-Unsubscribe /
List-Unsubscribe-Post. Also documents the puter-email driver's automatic
unsubscribe / report-abuse footer and the new `suppressed` result field
in the puter.js email module.

* feat(email): envelope override in sendRaw + suppressed in EmailSendResult type

Adds an optional `envelope` field to SendMailOptions so callers can set
transport recipients independently of the visible To/Cc headers (used by
the email-send driver for per-recipient deliveries), and adds the
`suppressed: string[]` field to the public EmailSendResult typing to
match the driver's documented result.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* feat(email): document per-recipient best-effort delivery via `failed`

The email-send driver now attempts every recipient's private delivery
even when one fails, returning failed addresses in the result's
`failed` array instead of failing the whole call — so callers retry
only the failed subset and never re-mail delivered recipients. Adds
the field to the public EmailSendResult typing and module docs.

src/backend/clients/email/EmailClient.ts

@@ -45,11 +45,18 @@ export interface SendMailOptions {
     to: string;
     cc?: string;
     bcc?: string;
+    /** Optional transport recipients when they differ from visible headers. */
+    envelope?: {
+        from?: string;
+        to: string;
+    };
     subject: string;
     html?: string;
     text?: string;
     replyTo?: string;
     attachments?: EmailAttachment[];
+    /** Extra message headers (e.g. List-Unsubscribe), passed to the transport. */
+    headers?: Record<string, string>;
 }
 
 export type EmailValidator = (email: string) => Promise<boolean> | boolean;

src/puter-js/src/modules/Email.js

@@ -22,6 +22,16 @@ import * as utils from '../lib/utils.js';
  *   });
  *
  * Positional form: `await puter.email.send(to, subject, body)`.
+ *
+ * Every mail automatically gets an unsubscribe / report-abuse footer.
+ * Recipients who unsubscribe are dropped from future sends — they come
+ * back in the result's `suppressed` array — and a send whose `to` list
+ * is entirely unsubscribed is rejected.
+ *
+ * Each recipient gets a private delivery. A recipient whose delivery
+ * fails comes back in the result's `failed` array (everyone else got
+ * their copy — retry with just those addresses); the call only rejects
+ * when no recipient could be delivered.
  */
 class Email {
     /**

src/puter-js/types/modules/email.d.ts

@@ -36,10 +36,18 @@ export interface EmailSendOptions {
 }
 
 export interface EmailSendResult {
-    /** Transport message id, when the mail server reports one. */
+    /** First transport message id reported for this send, when available. */
     messageId: string | null;
     /** Total charge for this send, in microcents. */
     cost: number;
+    /** Recipients omitted because they opted out of this sender's mail. */
+    suppressed: string[];
+    /**
+     * Recipients whose delivery attempt failed. Everyone else got their
+     * copy — retry with just these addresses. A send where every delivery
+     * fails rejects instead.
+     */
+    failed: string[];
 }
 
 /**