From 472a86698f60e165ac610dc6a340875e94b6f9e0 Mon Sep 17 00:00:00 2001
From: Sawyer Cutler <sawyer@dirtroad.dev>
Date: Mon, 21 Sep 2026 22:16:52 -0700
Subject: [PATCH] feat(mailbox): default mountMailbox's SSE bus to in-process
 (CL-8775)

---
 src/mount.ts | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/src/mount.ts b/src/mount.ts
index 4e6a09f..9bfaaff 100644
--- a/src/mount.ts
+++ b/src/mount.ts
@@ -8,6 +8,7 @@ import type { Thread } from "@intx/types/runtime";
 import type { MailboxDb } from "./db.js";
 import type { NativeMailboxStore } from "./native-store.js";
 import {
+  createInMemoryMailboxEventBus,
   publishMailboxEvent,
   type MailboxEvent,
   type MailboxEventBus,
@@ -30,7 +31,12 @@ export type OutgoingMailboxMessage = {
 
 export type MountMailboxOpts = {
   db: MailboxDb;
-  bus: MailboxEventBus;
+  /**
+   * SSE live-update bus only. Mail is Postgres. Defaults to an in-process
+   * bus (one hub process). Pass a shared bus if several hub processes must
+   * fan the same inbox events.
+   */
+  bus?: MailboxEventBus;
   resolvePrincipal: (
     ctx: unknown,
   ) => Promise<ResolvedPrincipal | null> | ResolvedPrincipal | null;
@@ -202,7 +208,8 @@ export function mountMailbox<E extends Env>(
   app: Hono<E>,
   opts: MountMailboxOpts,
 ): Hono<E> {
-  const { db, bus, resolvePrincipal, senderAddressFor, deliver } = opts;
+  const { db, resolvePrincipal, senderAddressFor, deliver } = opts;
+  const bus = opts.bus ?? createInMemoryMailboxEventBus();
   const heartbeatIntervalMs =
     opts.heartbeatIntervalMs ?? DEFAULT_HEARTBEAT_INTERVAL_MS;
   if (!Number.isFinite(heartbeatIntervalMs) || heartbeatIntervalMs <= 0) {