feat(observatory): bridge local M49 worker container

tests/test_observatory_m49_worker_container_main.py

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+from __future__ import annotations
+
+import socket
+import socketserver
+import threading
+
+import pytest
+
+import k1link.observatory.m49_worker_container_main as container_main
+
+
+class _EchoHandler(socketserver.BaseRequestHandler):
+    def handle(self) -> None:
+        payload = self.request.recv(1024)
+        self.request.sendall(payload)
+
+
+def test_fixed_container_proxy_bridges_loopback_without_gateway_override() -> None:
+    upstream = socketserver.ThreadingTCPServer(("127.0.0.1", 0), _EchoHandler)
+    upstream_thread = threading.Thread(target=upstream.serve_forever, daemon=True)
+    upstream_thread.start()
+    try:
+        upstream_port = upstream.server_address[1]
+        assert isinstance(upstream_port, int)
+        with container_main.FixedM49ContainerLoopbackProxy(
+            listen_port=0,
+            upstream_host="127.0.0.1",
+            upstream_port=upstream_port,
+        ) as proxy, socket.create_connection(
+            ("127.0.0.1", proxy.listen_port)
+        ) as client:
+            client.sendall(b"fixed-m49-proxy")
+            client.shutdown(socket.SHUT_WR)
+            assert client.recv(1024) == b"fixed-m49-proxy"
+    finally:
+        upstream.shutdown()
+        upstream.server_close()
+        upstream_thread.join(timeout=5.0)
+
+
+def test_container_entrypoint_owns_proxy_around_worker(monkeypatch: pytest.MonkeyPatch) -> None:
+    lifecycle: list[str] = []
+
+    class _Proxy:
+        def __enter__(self) -> _Proxy:
+            lifecycle.append("proxy-started")
+            return self
+
+        def __exit__(self, *_args: object) -> None:
+            lifecycle.append("proxy-stopped")
+
+    def worker(arguments: object) -> int:
+        lifecycle.append(f"worker:{arguments!r}")
+        return 17
+
+    monkeypatch.setattr(container_main, "FixedM49ContainerLoopbackProxy", _Proxy)
+    monkeypatch.setattr(container_main.m49_worker_service, "main", worker)
+
+    assert container_main.main(("--once",)) == 17
+    assert lifecycle == ["proxy-started", "worker:('--once',)", "proxy-stopped"]
+
+
+def test_container_proxy_refuses_non_loopback_listener() -> None:
+    with pytest.raises(ValueError, match="IPv4 loopback"):
+        container_main.FixedM49ContainerLoopbackProxy(listen_host="0.0.0.0")
+
+
+def test_production_proxy_endpoints_are_fixed() -> None:
+    assert container_main.M49_CONTAINER_PROXY_LISTEN_HOST == "127.0.0.1"
+    assert container_main.M49_CONTAINER_PROXY_LISTEN_PORT == 18080
+    assert container_main.M49_CONTAINER_PROXY_UPSTREAM_HOST == "host.docker.internal"
+    assert container_main.M49_CONTAINER_PROXY_UPSTREAM_PORT == 18080