feat(orchestrator): host control server transport (#468)

Chunk 1 of the host-control-server stack: close the PRD's **transport**
gap. Today LaunchBroker.submit(token) is an in-process method call from
OrchestratorCore; this makes it a real out-of-process service reached
over HTTP.

- host_server.py: the host control server. A pure dispatch() (POST
  /broker verifies a signed token via the existing verify_request +
  _launch/_teardown path, GET /health) wrapped by a thin http.server
  adapter, mirroring orchestrator/server.py. Only the signed token
  crosses the wire; provenance/schema failures are fail-closed 401s that
  never touch the backend, a backend launch failure is a 502.
- broker_client.py: BrokerClient — a drop-in submit(token) that POSTs the
  signed token to the host controller. A 401 re-raises as BrokerAuthError
  so the launch path's rollback is identical local or remote.
- broker.py: SubmitBroker Protocol — the one method OrchestratorCore
  depends on, satisfied by both LaunchBroker and BrokerClient, so the
  core is unchanged (service.py annotation only).
- __main__.py: wire `--broker http` behind the shared-secret env var
  (BOT_BOTTLE_BROKER_SECRET, hex) — a chunk-1 stopgap the durable
  TrustDomain key (chunk 2, #476) replaces.

Tested: pure-dispatch cases, BrokerClient with HTTP mocked, and a
real-socket sign -> POST -> verify -> act round-trip (incl. fail-closed
forged token). pyright clean; pylint 9.86.

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

bot_bottle/orchestrator/__main__.py

@@ -17,7 +17,9 @@ from pathlib import Path
 
 from .. import log
 from .store.store_manager import StoreManager
-from .broker import LaunchBroker, StubBroker
+from .broker import StubBroker, SubmitBroker
+from .broker_client import BrokerClient
+from .host_server import BROKER_SECRET_ENV, DEFAULT_PORT, broker_secret_from_env
 from .server import make_server
 from .docker_broker import DockerBroker
 from .store.registry_store import RegistryStore, default_db_path
@@ -34,8 +36,13 @@ def main(argv: list[str] | None = None) -> int:
         help=f"registry DB path (default: {default_db_path()})",
     )
     parser.add_argument(
-        "--broker", choices=("stub", "docker"), default="stub",
-        help="launch broker: 'stub' records requests; 'docker' runs containers",
+        "--broker", choices=("stub", "docker", "http"), default="stub",
+        help="launch broker: 'stub' records requests; 'docker' runs containers "
+             "in-process; 'http' relays signed requests to a host control server",
+    )
+    parser.add_argument(
+        "--host-controller-url", default=f"http://127.0.0.1:{DEFAULT_PORT}",
+        help="host control server URL (used only with --broker http)",
     )
     args = parser.parse_args(argv)
 
@@ -47,11 +54,25 @@ def main(argv: list[str] | None = None) -> int:
     # operator reaches it over HTTP (never a second, disconnected DB).
     StoreManager(registry.db_path).migrate()
 
-    # An ephemeral signing secret ties the orchestrator (signer) to its
-    # broker (verifier). 'stub' records launches instead of starting
-    # anything; 'docker' runs real containers (firecracker drops in later).
-    secret = secrets.token_bytes(32)
-    broker: LaunchBroker = DockerBroker(secret) if args.broker == "docker" else StubBroker(secret)
+    # A signing secret ties the orchestrator (signer) to its broker (verifier).
+    # 'stub' records launches instead of starting anything; 'docker' runs real
+    # containers in-process; 'http' relays signed requests to a separate host
+    # control server, which verifies and launches. For 'stub'/'docker' the
+    # secret is ephemeral (signer and verifier share this process); for 'http'
+    # it must be the SAME secret the host controller holds, so it is read from
+    # the shared env var (the chunk-1 stand-in for out-of-band provisioning).
+    broker: SubmitBroker
+    if args.broker == "http":
+        secret = broker_secret_from_env()
+        if secret is None:
+            parser.error(
+                f"--broker http requires a shared signing secret in "
+                f"${BROKER_SECRET_ENV} (hex), matching the host control server"
+            )
+        broker = BrokerClient(args.host_controller_url)
+    else:
+        secret = secrets.token_bytes(32)
+        broker = DockerBroker(secret) if args.broker == "docker" else StubBroker(secret)
     orchestrator = OrchestratorCore(registry, broker, secret)
 
     server = make_server(orchestrator, host=args.host, port=args.port)