feat(orchestrator): durable launch-broker secret via TrustDomain (#468)

Chunk 2 of the host-control-server stack: close the PRD's **durable
secret** gap and replace chunk 1's BOT_BOTTLE_BROKER_SECRET stopgap.

- trust_domain.py: two new domains. LAUNCH_BROKER holds the durable
  HS256 key both the orchestrator (signer) and the host control server
  (verifier) share for the broker's launch JWT — a host-canonical key
  file minted 0600 on first use, so a restarted orchestrator re-verifies
  against the same key. HOST_CONTROLLER is the separate domain for the
  controller's own lifecycle endpoints, keyed by a key the orchestrator
  never holds (its role is `host`, deliberately outside control-plane
  ROLES). LaunchBrokerProvisioning is the fail-closed seam.
- orchestrator_auth.py: ROLE_HOST, outside ROLES.
- paths.py: key-file + env-var constants for both domains.

Key resolution is split by owner (addresses codex review on #497):
broker_secret(allow_host_file=...) — the host controller / dev-harness
(True) may mint/read the durable host key file it owns; the GUEST
orchestrator (--broker http, default False) must be *injected* the key
and fails closed if it isn't. A guest that fell back to the host file
would mint a process-local key unrelated to the host controller's, so
startup would succeed but every launch would 401 — this prevents that
silent divergence.

Tested: domain boundary + separation, provisioning fail-closed, and
broker_secret env-only (guest) vs host-file (host) resolution. pyright
clean; pylint 9.86.

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

bot_bottle/orchestrator/__main__.py

@@ -17,9 +17,10 @@ from pathlib import Path
 
 from .. import log
 from .store.store_manager import StoreManager
+from ..paths import LAUNCH_BROKER_KEY_ENV
 from .broker import StubBroker, SubmitBroker
 from .broker_client import BrokerClient
-from .host_server import BROKER_SECRET_ENV, DEFAULT_PORT, broker_secret_from_env
+from .host_server import DEFAULT_PORT, broker_secret
 from .server import make_server
 from .docker_broker import DockerBroker
 from .store.registry_store import RegistryStore, default_db_path
@@ -57,17 +58,19 @@ def main(argv: list[str] | None = None) -> int:
     # 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).
+    # 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 key the host controller holds — and this process is the *guest*
+    # (signer), so it must be given that key by injection, NOT mint its own
+    # process-local one (which would diverge from the host's and 401 every launch).
     broker: SubmitBroker
     if args.broker == "http":
-        secret = broker_secret_from_env()
+        secret = broker_secret()  # env-injected only; no host-file fallback here
         if secret is None:
             parser.error(
-                f"--broker http requires a shared signing secret in "
-                f"${BROKER_SECRET_ENV} (hex), matching the host control server"
+                f"--broker http requires the launch-broker key injected as "
+                f"${LAUNCH_BROKER_KEY_ENV} (the host controller owns/mints it); the "
+                "orchestrator must not mint its own or it would diverge from the host's"
             )
         broker = BrokerClient(args.host_controller_url)
     else: