diff --git a/packages/runtime/src/io/frame-writer.ts b/packages/runtime/src/io/frame-writer.ts
index 639fed6..3b49b70 100644
--- a/packages/runtime/src/io/frame-writer.ts
+++ b/packages/runtime/src/io/frame-writer.ts
@@ -10,7 +10,9 @@ export function createFrameWriter(
   stream: NodeJS.WriteStream,
   options: { debug?: boolean },
 ): FrameWriter {
-  let lastFrame = "";
+  // Sentinel: use a value that can never equal a real frame so the very first
+  // write (even an empty string) is always emitted.
+  let lastFrame: string | null = null;
   const debug = options.debug ?? false;
   const update = debug ? null : createLogUpdate(stream);
 
@@ -28,7 +30,7 @@ export function createFrameWriter(
       if (update) update.done();
     },
     clear() {
-      lastFrame = "";
+      lastFrame = null;
       if (update) update.clear();
     },
   };