ui: default to Completion+code (matches cached trace); clear textbox on switch to Chat, restore seed on switch back if empty

demo/srt_introspect_app.py

@@ -760,19 +760,24 @@ def build_app() -> gr.Blocks:
         with gr.Row():
             with gr.Column(scale=3):
                 mode = gr.Radio(
-                    choices=["Chat", "Completion"],
-                    value="Chat",
+                    choices=["Completion", "Chat"],
+                    value="Completion",
                     label="Input mode",
                     info=(
-                        "Chat: type a question or instruction naturally; "
-                        "we wrap it as User:/Assistant: for the base model. "
                         "Completion: feed the prompt raw (good for code, "
-                        "narrative, or mid-sentence continuations)."
+                        "narrative, or mid-sentence continuations). "
+                        "Chat: type a question or instruction naturally; "
+                        "we wrap it as User:/Assistant: for the base model."
                     ),
                 )
                 prompt = gr.Textbox(
                     label="Prompt",
-                    value="Explain why warm water sometimes freezes faster than cold water.",
+                    value=(
+                        "def quicksort(arr):\n"
+                        "    if len(arr) <= 1:\n"
+                        "        return arr\n"
+                        "    pivot = arr[len(arr) // 2]\n"
+                    ),
                     lines=6,
                 )
             with gr.Column(scale=2):
@@ -822,6 +827,30 @@ def build_app() -> gr.Blocks:
         )
         stop.click(fn=None, cancels=[gen_event])
 
+        # Default code prompt only makes sense in Completion mode. When the
+        # user switches to Chat, blank the textbox so they don't try to chat
+        # with `def quicksort(...)`; when they switch back to Completion,
+        # restore the code seed so the textbox isn't stranded empty.
+        _COMPLETION_DEFAULT = (
+            "def quicksort(arr):\n"
+            "    if len(arr) <= 1:\n"
+            "        return arr\n"
+            "    pivot = arr[len(arr) // 2]\n"
+        )
+
+        def _on_mode_change(new_mode: str, current: str):
+            if (new_mode or "").lower().startswith("chat"):
+                # Only clear if the user hasn't edited the default code seed.
+                if current.strip() == _COMPLETION_DEFAULT.strip():
+                    return gr.update(value="", placeholder="Ask anything…")
+                return gr.update(placeholder="Ask anything…")
+            # Switched to Completion: restore code seed only if textbox is empty.
+            if not current.strip():
+                return gr.update(value=_COMPLETION_DEFAULT, placeholder=None)
+            return gr.update(placeholder=None)
+
+        mode.change(_on_mode_change, inputs=[mode, prompt], outputs=[prompt])
+
         gr.Markdown(f"""
 ---