diff --git a/src/auto-reply/inbound-debounce.ts b/src/auto-reply/inbound-debounce.ts
index 194dee6f0c2..078e9567e3e 100644
--- a/src/auto-reply/inbound-debounce.ts
+++ b/src/auto-reply/inbound-debounce.ts
@@ -86,11 +86,12 @@ export function createInboundDebouncer<T>(params: InboundDebounceCreateParams<T>
     const next = previous.catch(() => undefined).then(task);
     const settled = next.catch(() => undefined);
     keyChains.set(key, settled);
-    void settled.finally(() => {
+    const cleanup = () => {
       if (keyChains.get(key) === settled) {
         keyChains.delete(key);
       }
-    });
+    };
+    settled.then(cleanup, cleanup);
     return next;
   };
 
diff --git a/src/auto-reply/inbound.test.ts b/src/auto-reply/inbound.test.ts
index 6a47db79161..d8bd1d76be9 100644
--- a/src/auto-reply/inbound.test.ts
+++ b/src/auto-reply/inbound.test.ts
@@ -521,6 +521,29 @@ describe("createInboundDebouncer", () => {
     expect(calls).toEqual(["1", "2"]);
   });
 
+  it("does not leak unhandled rejections when a keyed flush failure is awaited", async () => {
+    const debouncer = createInboundDebouncer<{ key: string; id: string }>({
+      debounceMs: 0,
+      buildKey: (item) => item.key,
+      onFlush: async () => {
+        throw new Error("flush failed");
+      },
+    });
+    const unhandled: unknown[] = [];
+    const onUnhandledRejection = (reason: unknown) => {
+      unhandled.push(reason);
+    };
+    process.on("unhandledRejection", onUnhandledRejection);
+
+    try {
+      await expect(debouncer.enqueue({ key: "a", id: "1" })).resolves.toBeUndefined();
+      await new Promise((resolve) => setTimeout(resolve, 0));
+      expect(unhandled).toEqual([]);
+    } finally {
+      process.off("unhandledRejection", onUnhandledRejection);
+    }
+  });
+
   it("bypasses debouncing for new keys once the tracked-key cap is reached", async () => {
     vi.useFakeTimers();
     const calls: Array<string[]> = [];