fix(observability): log send rate limit hits

workers/index.ts

@@ -20,6 +20,7 @@ import { handleReplyEmail, handleForwardEmail } from "./routes/reply-forward";
 import { Folders } from "../shared/folders";
 import type { Env } from "./types";
 import { requireMailbox, type MailboxContext } from "./lib/mailbox";
+import { logSendRateLimitHit } from "./lib/rate-limit";
 
 type AppContext = Context<MailboxContext>;
 
@@ -181,7 +182,10 @@ app.post("/api/v1/mailboxes/:mailboxId/emails", async (c: AppContext) => {
 	const { messageId, outgoingMessageId } = generateMessageId(fromDomain);
 	const stub = c.var.mailboxStub;
 	const rateLimitError = await (stub as any).checkSendRateLimit();
-	if (rateLimitError) return c.json({ error: rateLimitError }, 429);
+	if (rateLimitError) {
+		logSendRateLimitHit(mailboxId, "api.sendEmail", rateLimitError);
+		return c.json({ error: rateLimitError }, 429);
+	}
 	const attachmentData = await storeAttachments(c.env.BUCKET, messageId, attachments);
 
 	await stub.createEmail(Folders.SENT, {

workers/lib/rate-limit.ts

@@ -0,0 +1,11 @@
+// Copyright (c) 2026 Cloudflare, Inc.
+// Licensed under the Apache 2.0 license found in the LICENSE file or at:
+//     https://opensource.org/licenses/Apache-2.0
+
+export function logSendRateLimitHit(
+	mailboxId: string,
+	source: string,
+	error: string,
+) {
+	console.warn("Send rate limit hit", { mailboxId, source, error });
+}

workers/lib/tools.ts

@@ -27,6 +27,7 @@ import {
 	buildThreadingHeaders,
 } from "./email-helpers";
 import { verifyDraft } from "./ai";
+import { logSendRateLimitHit } from "./rate-limit";
 import { sendEmail } from "../email-sender";
 import { Folders } from "../../shared/folders";
 import type { Env } from "../types";
@@ -408,6 +409,7 @@ export async function toolSendReply(
 	// Check send rate limit
 	const rateLimitError = await (stub as unknown as RateLimitStub).checkSendRateLimit();
 	if (rateLimitError) {
+		logSendRateLimitHit(mailboxId, "tool.sendReply", rateLimitError);
 		return { error: rateLimitError };
 	}
 
@@ -486,6 +488,7 @@ export async function toolSendEmail(
 	// Check send rate limit
 	const rateLimitError = await (stub as unknown as RateLimitStub).checkSendRateLimit();
 	if (rateLimitError) {
+		logSendRateLimitHit(mailboxId, "tool.sendEmail", rateLimitError);
 		return { error: rateLimitError };
 	}
 

workers/routes/reply-forward.ts

@@ -17,6 +17,7 @@ import {
 import { SendEmailRequestSchema } from "../lib/schemas";
 import { Folders } from "../../shared/folders";
 import type { MailboxContext } from "../lib/mailbox";
+import { logSendRateLimitHit } from "../lib/rate-limit";
 
 type AppContext = Context<MailboxContext>;
 type RateLimitStub = { checkSendRateLimit: () => Promise<string | null> };
@@ -50,6 +51,7 @@ export async function handleReplyEmail(c: AppContext) {
 	const rateLimitError = await (stub as unknown as RateLimitStub)
 		.checkSendRateLimit();
 	if (rateLimitError) {
+		logSendRateLimitHit(mailboxId, "api.replyEmail", rateLimitError);
 		return c.json({ error: rateLimitError }, 429);
 	}
 
@@ -140,6 +142,7 @@ export async function handleForwardEmail(c: AppContext) {
 	const rateLimitError = await (stub as unknown as RateLimitStub)
 		.checkSendRateLimit();
 	if (rateLimitError) {
+		logSendRateLimitHit(mailboxId, "api.forwardEmail", rateLimitError);
 		return c.json({ error: rateLimitError }, 429);
 	}