From de4657288ff34043aebc5ce0006655a9553287d8 Mon Sep 17 00:00:00 2001
From: Zach Halzel <zahalzel@microsoft.com>
Date: Fri, 17 Apr 2026 14:12:32 -0400
Subject: [PATCH] fix: avoid spurious unhandledRejection when transport fails
 mid-sendRequest

If the transport fails (or #receive observes stream closure) while sendRequest is awaiting #sendMessage, #close() rejects the response promise before the caller's await has attached a handler. Node then reports a spurious unhandledRejection (followed by PromiseRejectionHandledWarning), even though the caller's await does observe the rejection.

Attach a noop .catch to responsePromise so the rejection is considered handled at the time it's raised. The rejection is still delivered to the caller verbatim via 'return responsePromise'.
---
 src/acp.ts | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/acp.ts b/src/acp.ts
index 51355bf..0693a72 100644
--- a/src/acp.ts
+++ b/src/acp.ts
@@ -1468,6 +1468,14 @@ class Connection {
     const responsePromise = new Promise((resolve, reject) => {
       this.pendingResponses.set(id, { resolve, reject });
     });
+    // If the transport fails (or receive observes stream closure) during the
+    // `await sendMessage` below, close() will reject `responsePromise`
+    // before the caller has had a chance to attach its own handler. Node then
+    // reports a spurious `unhandledRejection`, even though the caller's
+    // subsequent `await` does observe the rejection. Attach a noop catch so
+    // the rejection is considered handled at the time it's raised; the
+    // rejection is still delivered to the caller via `return responsePromise`.
+    responsePromise.catch(() => {});
     await this.sendMessage({ jsonrpc: "2.0", id, method, params });
     return responsePromise as Promise<Resp>;
   }