fix: clear template on keydown via JS + CodeMirror cmView API, drop broken Python handler

app.py

@@ -369,6 +369,7 @@ def build_app() -> gr.Blocks:
                     language="python",
                     lines=20,
                     value="# Write your solution here using Legesher\n# Use native-language variable and function names\n",
+                    elem_id="legesher-code-editor",
                 )
 
                 with gr.Row():
@@ -414,33 +415,9 @@ def build_app() -> gr.Blocks:
         # ---- State ----
         tier_idx_state = gr.State(value=0)
         lang_state = gr.State(value="zh")
-        template_cleared = gr.State(value=False)
 
         # ---- Event wiring ----
 
-        _T1 = "# Write your solution here using Legesher"
-        _T2 = "# Use native-language variable and function names"
-        _TEMPLATE = f"{_T1}\n{_T2}\n"
-
-        def on_code_change(code: str, cleared: bool):
-            """On the user's first real edit, strip the template strings then never run again."""
-            if cleared:
-                return gr.update(), True
-            # Nothing typed yet — template still untouched
-            if code.strip() in ("", _T1, _T2, f"{_T1}\n{_T2}"):
-                return gr.update(), False
-            # Strip the two template lines wherever they appear via substring replace
-            cleaned = code.replace(_T1 + "\n", "").replace(_T2 + "\n", "")
-            cleaned = cleaned.replace(_T1, "").replace(_T2, "")
-            cleaned = cleaned.lstrip("\n")
-            return cleaned, True
-
-        code_editor.change(
-            fn=on_code_change,
-            inputs=[code_editor, template_cleared],
-            outputs=[code_editor, template_cleared],
-        )
-
         def tier_to_idx(tier_label: str) -> int:
             return TIER_LABELS.index(tier_label)
 
@@ -504,8 +481,8 @@ def build_app() -> gr.Blocks:
         )
 
         clear_btn.click(
-            fn=lambda: ("# Write your solution here using Legesher\n# Use native-language variable and function names\n", "", "", False),
-            outputs=[code_editor, stdin_input, run_output, template_cleared],
+            fn=lambda: ("# Write your solution here using Legesher\n# Use native-language variable and function names\n", "", ""),
+            outputs=[code_editor, stdin_input, run_output],
         )
 
         submit_btn.click(
@@ -521,6 +498,36 @@ def build_app() -> gr.Blocks:
             outputs=[submit_status],
         )
 
+        # ---- JS: clear template on first keystroke (client-side, no server round-trip) ----
+        _CLEAR_TEMPLATE_JS = """
+        function() {
+            const T1 = '# Write your solution here using Legesher';
+            const T2 = '# Use native-language variable and function names';
+
+            function clearTemplate(view) {
+                const doc = view.state.doc.toString();
+                if (!doc.includes(T1) && !doc.includes(T2)) return;
+                let cleaned = doc
+                    .replace(T1 + '\\n', '').replace(T2 + '\\n', '')
+                    .replace(T1, '').replace(T2, '');
+                cleaned = cleaned.replace(/^\\n+/, '');
+                view.dispatch({
+                    changes: { from: 0, to: view.state.doc.length, insert: cleaned },
+                    selection: { anchor: 0 }
+                });
+            }
+
+            function setup() {
+                const wrap = document.querySelector('#legesher-code-editor .cm-editor');
+                if (!wrap || !wrap.cmView) { setTimeout(setup, 300); return; }
+                wrap.addEventListener('keydown', () => clearTemplate(wrap.cmView), true);
+            }
+
+            setTimeout(setup, 600);
+        }
+        """
+        app.load(fn=None, js=_CLEAR_TEMPLATE_JS)
+
     return app