diff --git a/crates/buzz-agent/tests/fake_llm.rs b/crates/buzz-agent/tests/fake_llm.rs
index 4253ef329c..88050b5b1e 100644
--- a/crates/buzz-agent/tests/fake_llm.rs
+++ b/crates/buzz-agent/tests/fake_llm.rs
@@ -1266,7 +1266,7 @@ async fn cancelled_turn_with_usage_emits_notification_before_response() {
     // in-flight TCP request can resolve. The queue is empty for round 2, so the
     // agent receives the fallback "no canned response" body which it treats as
     // an LLM error; the cancel check at the round boundary fires first because
-    // the gate is only released after cancel is enqueued.
+    // the gate is only released after cancel is acknowledged.
     let responses = vec![openai_tool_call_with_usage(
         "call_cancel_test",
         "fake__noop",
@@ -1346,20 +1346,25 @@ async fn cancelled_turn_with_usage_emits_notification_before_response() {
     })
     .await;
 
-    // Now send cancel and release the round-2 gate. Cancel is enqueued before
-    // round 2 can respond, so the turn exits with stopReason: cancelled.
+    // Wait for the cancel acknowledgement before releasing the round-2 gate.
+    // Sending only proves the request was written to stdin; the acknowledgement
+    // proves the agent processed it before round 2 can respond.
     let c_id = h.send("session/cancel", json!({"sessionId": sid})).await;
+    let (frames_before_cancel_ack, _) =
+        recv_until_with_drain(&mut h, |v| v["id"] == json!(c_id)).await;
     let _ = gate_tx.send(()); // unblock round 2
 
     let mut saw_usage_before_prompt_response = false;
     let mut saw_usage = false;
-    let mut saw_cancel_ok = false;
     let mut saw_prompt_response = false;
-    for _ in 0..40 {
-        let v = h.recv().await;
-        if v["id"] == json!(c_id) {
-            saw_cancel_ok = true;
-        } else if is_usage_update(&v) {
+    let mut pending_frames = VecDeque::from(frames_before_cancel_ack);
+    let frame_budget = 40 + pending_frames.len();
+    for _ in 0..frame_budget {
+        let v = match pending_frames.pop_front() {
+            Some(v) => v,
+            None => h.recv().await,
+        };
+        if is_usage_update(&v) {
             saw_usage = true;
             if !saw_prompt_response {
                 saw_usage_before_prompt_response = true;
@@ -1372,11 +1377,10 @@ async fn cancelled_turn_with_usage_emits_notification_before_response() {
                 "turn must end with stopReason: cancelled"
             );
         }
-        if saw_usage && saw_prompt_response && saw_cancel_ok {
+        if saw_usage && saw_prompt_response {
             break;
         }
     }
-    assert!(saw_cancel_ok, "session/cancel was not acknowledged");
     assert!(
         saw_usage,
         "expected usage_update notification for cancelled turn with observed tokens"