diff --git a/swe_af/app.py b/swe_af/app.py
index af855a3..3b38624 100644
--- a/swe_af/app.py
+++ b/swe_af/app.py
@@ -2118,7 +2118,13 @@ async def resume_build(
 
 def main():
     """Entry point for ``python -m swe_af`` and the ``swe-af`` console script."""
-    app.run(port=8003, host="0.0.0.0")
+    # Don't hardcode the port: the AgentField control plane assigns a free port
+    # per launch and passes it via the PORT env var, then polls readiness on
+    # that port. The SDK's Agent.run() reads PORT when no port is given (and
+    # auto-selects a free port when run standalone), so leaving it unset is what
+    # lets `af run` work. Passing port=8003 bound the wrong port and made the
+    # control plane's readiness check time out ("did not become ready").
+    app.run(host="0.0.0.0")
 
 
 if __name__ == "__main__":
diff --git a/tests/test_main_entrypoint.py b/tests/test_main_entrypoint.py
new file mode 100644
index 0000000..418651b
--- /dev/null
+++ b/tests/test_main_entrypoint.py
@@ -0,0 +1,32 @@
+"""Contract test for the ``python -m swe_af`` entry point.
+
+The AgentField control plane assigns a free port per launch, passes it via the
+``PORT`` env var, and polls readiness on that port. ``main()`` must therefore
+NOT hardcode a port — it must let the SDK's ``Agent.run()`` read ``PORT`` (or
+auto-select a free port when run standalone). Passing an explicit port bound the
+wrong one and made the control plane's readiness check time out
+("agent node did not become ready within 10s").
+"""
+from __future__ import annotations
+
+import os
+
+os.environ.setdefault("AGENTFIELD_SERVER", "http://localhost:9999")
+
+import swe_af.app as app_module
+
+
+def test_main_does_not_hardcode_a_port(monkeypatch):
+    captured: dict = {}
+
+    def fake_run(*args, **kwargs):
+        captured["args"] = args
+        captured["kwargs"] = kwargs
+
+    monkeypatch.setattr(app_module.app, "run", fake_run)
+    app_module.main()
+
+    assert not captured["args"], "main() must not pass a positional port to app.run()"
+    assert "port" not in captured["kwargs"], (
+        "main() must not hardcode a port; the SDK reads PORT from the control plane"
+    )