diff --git a/agent/context/jsapi_output_test.go b/agent/context/jsapi_output_test.go
index 91592ffd..b657addb 100644
--- a/agent/context/jsapi_output_test.go
+++ b/agent/context/jsapi_output_test.go
@@ -1276,6 +1276,11 @@ func TestJsValueSendVsSendStream(t *testing.T) {
 			t.Fatalf("Call failed: %v", err)
 		}
 
+		// Close SafeWriter to flush all pending async writes before reading buffer.
+		// SafeWriter processes writes in a background goroutine via channel;
+		// without this, the buffer may still be empty on slow CI runners.
+		cxt.CloseSafeWriter()
+
 		output := mockWriter.buffer.String()
 		assert.Contains(t, output, "message_start", "Send should emit message_start")
 		assert.Contains(t, output, "message_end", "Send should auto-emit message_end")
@@ -1300,6 +1305,9 @@ func TestJsValueSendVsSendStream(t *testing.T) {
 			t.Fatalf("Call failed: %v", err)
 		}
 
+		// Close SafeWriter to flush all pending async writes before reading buffer.
+		cxt.CloseSafeWriter()
+
 		output := mockWriter.buffer.String()
 		assert.Contains(t, output, "message_start", "SendStream should emit message_start")
 		assert.NotContains(t, output, "message_end", "SendStream should NOT auto-emit message_end")