From 457fa8b6b2f6ddfd318c5022a7289083e544b2b1 Mon Sep 17 00:00:00 2001
From: David Lechner <david@lechnology.com>
Date: Sun, 25 Jan 2026 20:23:00 +0000
Subject: [PATCH] usb/sagas: Fix command response race condition

Fix a race condition where a response to a USB command could be missed
if it arrives before the USB transferOut() call returns. This is done
by using a channel to buffer incoming responses.

Fixes: https://github.com/pybricks/support/issues/2467
---
 src/usb/sagas.ts | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/usb/sagas.ts b/src/usb/sagas.ts
index 570df488..eb9a1c96 100644
--- a/src/usb/sagas.ts
+++ b/src/usb/sagas.ts
@@ -454,6 +454,12 @@ function* handleUsbConnectPybricks(hotPlugDevice?: USBDevice): Generator {
                 writeCommand.matches(a),
         );
 
+        // Response may come before request returns, so we need to buffer them
+        // in a channel to avoid missing responses.
+        const responseChannel = yield* actionChannel(
+            usbDidReceivePybricksMessageResponse,
+        );
+
         for (;;) {
             const action = yield* take(chan);
 
@@ -525,7 +531,7 @@ function* handleUsbConnectPybricks(hotPlugDevice?: USBDevice): Generator {
                 }
 
                 const { response, timeout } = yield* race({
-                    response: take(usbDidReceivePybricksMessageResponse),
+                    response: take(responseChannel),
                     timeout: delay(1000),
                 });