BISECT: temporarily swap build_app() with minimal probe via BISECT_MINIMAL=1

Dockerfile

@@ -29,6 +29,7 @@ EXPOSE 7860
 ENV GRADIO_SERVER_NAME=0.0.0.0 \
     GRADIO_SERVER_PORT=7860 \
     GRADIO_ANALYTICS_ENABLED=False \
-    PYTHONUNBUFFERED=1
+    PYTHONUNBUFFERED=1 \
+    BISECT_MINIMAL=1
 
 CMD ["python", "app.py"]

app.py

@@ -4991,6 +4991,18 @@ def run_self_test() -> int:
 
 if "--self-test" in sys.argv:
     demo = None
+elif os.environ.get("BISECT_MINIMAL") == "1":
+    # Diagnostic bisect: if the App tab shows this minimal page, then the
+    # full build_app() Blocks tree is what breaks iframe rendering. If it
+    # ALSO shows nothing, the problem is outside build_app (Docker, port
+    # routing, allowed_paths, etc).
+    with gr.Blocks(title="The Apprentice — bisect probe") as demo:
+        gr.Markdown("# BISECT PROBE")
+        gr.Markdown(
+            "If you can read this, the Docker + Gradio + iframe layers work. "
+            "The full build_app() Blocks tree is what's breaking rendering."
+        )
+        gr.Button("Click me").click(lambda: "ok", outputs=gr.Textbox())
 else:
     demo = build_app()