fix(orchestrator): address review on host control server transport (#468)

Codex review on #496:

- **High — ambiguous delivery no longer orphans a launched bottle.** A
  timeout / dropped response from the host controller is now the ambiguous
  BrokerUnavailableError (distinct from the definite BrokerAuthError /
  BrokerClientError). OrchestratorCore.launch_bottle keeps the registry
  row on the ambiguous case instead of deregistering — deregistering would
  orphan a running container with no record (reconcile reaps rows, never
  containers). The row is left for reconcile to reap iff the bottle is not
  actually live. Definite failures still roll back, so a real failure
  leaves no orphan row.
- **Medium — the privileged endpoint bounds request bodies.** The host
  server rejects an oversized Content-Length with 413 before reading it,
  and sets a per-request socket timeout, so a caller that can merely reach
  the socket (no signed token) can't exhaust memory or a handler thread.

Tests: ambiguous-keep vs definite-rollback in the launch path; the
BrokerUnavailableError/BrokerClientError split in BrokerClient; the 413
body cap + handler error paths (driven in-thread, since daemon request
threads lose coverage) plus a deterministic real-socket check that
declares an oversized Content-Length but sends a sliver (rejection on the
header, no unread-body reset race); and the __main__ entrypoint broker
selection. Diff-coverage 98%; pyright clean; pylint 9.8.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/unit/test_orchestrator_host_server.py

@@ -7,10 +7,14 @@ the full sign -> POST -> verify -> act seam over HTTP.
 
 from __future__ import annotations
 
+import http.client
+import io
 import json
 import secrets
 import threading
+import typing
 import unittest
+from unittest.mock import MagicMock, patch
 
 from bot_bottle.orchestrator.broker import (
     BrokerAuthError,
@@ -21,8 +25,12 @@ from bot_bottle.orchestrator.broker import (
 )
 from bot_bottle.orchestrator.broker_client import BrokerClient
 from bot_bottle.orchestrator.host_server import (
+    MAX_BODY_BYTES,
+    Handler,
+    HostControlServer,
     broker_secret_from_env,
     dispatch,
+    main,
     make_host_server,
 )
 
@@ -97,6 +105,16 @@ class TestDispatch(unittest.TestCase):
         status, _ = dispatch(self.broker, "POST", "/broker", b"{not json")
         self.assertEqual(400, status)
 
+    def test_empty_body_is_missing_token_400(self) -> None:
+        # Empty body parses to {} (no token) → 400, never reaching the broker.
+        status, _ = dispatch(self.broker, "POST", "/broker", b"")
+        self.assertEqual(400, status)
+        self.assertEqual([], self.broker.launched)
+
+    def test_non_object_body_is_400(self) -> None:
+        status, _ = dispatch(self.broker, "POST", "/broker", b"[1, 2]")
+        self.assertEqual(400, status)
+
     def test_unknown_route_404(self) -> None:
         status, _ = dispatch(self.broker, "GET", "/nope", b"")
         self.assertEqual(404, status)
@@ -152,5 +170,116 @@ class TestSeamRoundTrip(unittest.TestCase):
         self.assertEqual([], broker.launched)  # fail-closed across the wire
 
 
+class TestRequestLimits(unittest.TestCase):
+    """The privileged listener must not let a caller that can merely reach the
+    socket (no signed token) exhaust it via an oversized declared body — and it
+    rejects on the Content-Length *header*, before reading the body."""
+
+    def _addr(self) -> tuple[str, int]:
+        self.broker = StubBroker(secrets.token_bytes(16))
+        server = make_host_server(self.broker, "127.0.0.1", 0)
+        self.addCleanup(server.server_close)
+        threading.Thread(target=server.serve_forever, daemon=True).start()
+        self.addCleanup(server.shutdown)
+        host, port = server.server_address[:2]
+        return typing.cast(str, host), port
+
+    def test_oversized_content_length_is_rejected_before_reading(self) -> None:
+        host, port = self._addr()
+        conn = http.client.HTTPConnection(host, port, timeout=5)
+        self.addCleanup(conn.close)
+        # Declare an oversized body but send only a sliver: the server must reject
+        # on the header before reading, so the caller gets a clean, deterministic
+        # 413 (no large unread body to race a connection reset).
+        conn.putrequest("POST", "/broker", skip_accept_encoding=True)
+        conn.putheader("Content-Type", "application/json")
+        conn.putheader("Content-Length", str(MAX_BODY_BYTES + 1))
+        conn.endheaders()
+        conn.send(b"{}")  # far short of the declared length; never read
+        resp = conn.getresponse()
+        self.assertEqual(413, resp.status)
+        self.assertEqual([], self.broker.launched)  # never reached the broker
+
+
+class TestServeUnit(unittest.TestCase):
+    """Drive `Handler._serve` directly (no socket). The real per-request handler
+    runs in a daemon thread whose coverage/trace data is lost, so the
+    bounded-body and error paths are exercised here in the main thread instead."""
+
+    def _handler(self, broker: LaunchBroker, headers: dict[str, str],
+                 body: bytes = b"") -> tuple[Handler, MagicMock]:
+        server = HostControlServer.__new__(HostControlServer)
+        server.broker = broker
+        h = Handler.__new__(Handler)
+        h.server = server
+        h.headers = headers  # type: ignore[assignment] — dict is a valid .get() stand-in
+        h.path = "/broker"
+        h.rfile = io.BytesIO(body)
+        h.wfile = io.BytesIO()
+        send_response = MagicMock()
+        h.send_response = send_response  # type: ignore[method-assign]
+        h.send_header = MagicMock()  # type: ignore[method-assign]
+        h.end_headers = MagicMock()  # type: ignore[method-assign]
+        return h, send_response
+
+    def test_oversized_content_length_is_413(self) -> None:
+        broker = StubBroker(secrets.token_bytes(16))
+        h, send_response = self._handler(broker, {"Content-Length": str(MAX_BODY_BYTES + 1)})
+        h.do_POST()  # exercises do_POST -> _serve
+        send_response.assert_called_once_with(413)
+        self.assertEqual([], broker.launched)  # rejected before the broker
+
+    def test_invalid_content_length_is_400(self) -> None:
+        h, send_response = self._handler(StubBroker(secrets.token_bytes(16)),
+                                         {"Content-Length": "not-a-number"})
+        h._serve("POST")
+        send_response.assert_called_once_with(400)
+
+    def test_valid_request_dispatches_200(self) -> None:
+        secret = secrets.token_bytes(16)
+        broker = StubBroker(secret)
+        body = _body({"token": sign_request(
+            LaunchRequest(op="teardown", bottle_id="b1"), secret)})
+        h, send_response = self._handler(broker, {"Content-Length": str(len(body))}, body)
+        h._serve("POST")
+        send_response.assert_called_once_with(200)
+        self.assertEqual(["b1"], [r.bottle_id for r in broker.torn_down])
+
+    def test_dispatch_exception_becomes_500(self) -> None:
+        # dispatch is total, but the handler still guards it: a raised dispatch
+        # returns 500 rather than dropping the connection.
+        h, send_response = self._handler(
+            StubBroker(secrets.token_bytes(16)), {"Content-Length": "0"})
+        with patch("bot_bottle.orchestrator.host_server.dispatch",
+                   side_effect=RuntimeError("boom")):
+            h._serve("POST")
+        send_response.assert_called_once_with(500)
+
+    def test_health_over_do_get(self) -> None:
+        h, send_response = self._handler(StubBroker(secrets.token_bytes(16)), {})
+        h.path = "/health"
+        h.do_GET()
+        send_response.assert_called_once_with(200)
+
+
+class TestMain(unittest.TestCase):
+    def test_fail_closed_without_secret(self) -> None:
+        with patch("bot_bottle.orchestrator.host_server.broker_secret_from_env",
+                   return_value=None):
+            self.assertEqual(2, main(["--port", "0"]))
+
+    def test_serves_then_shuts_down_cleanly(self) -> None:
+        fake = MagicMock()
+        fake.server_address = ("127.0.0.1", 0)
+        fake.serve_forever.side_effect = KeyboardInterrupt
+        with patch("bot_bottle.orchestrator.host_server.broker_secret_from_env",
+                   return_value=b"k"), \
+             patch("bot_bottle.orchestrator.host_server.make_host_server",
+                   return_value=fake):
+            self.assertEqual(0, main(["--port", "0"]))
+        fake.serve_forever.assert_called_once()
+        fake.server_close.assert_called_once()
+
+
 if __name__ == "__main__":
     unittest.main()