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>

tests/unit/test_trust_domain.py

@@ -6,10 +6,13 @@ import unittest
 from unittest.mock import patch
 
 from bot_bottle import orchestrator_auth
-from bot_bottle.orchestrator_auth import ROLE_CLI, ROLE_GATEWAY
+from bot_bottle.orchestrator_auth import ROLE_CLI, ROLE_GATEWAY, ROLE_HOST
 from bot_bottle.trust_domain import (
     CONTROL_PLANE,
+    HOST_CONTROLLER,
+    LAUNCH_BROKER,
     ControlPlaneProvisioning,
+    LaunchBrokerProvisioning,
     ProvisioningError,
     TrustDomain,
 )
@@ -101,5 +104,73 @@ class TestControlPlaneProvisioning(unittest.TestCase):
         self.assertNotEqual(ROLE_CLI, CONTROL_PLANE.verify(tok, "k"))
 
 
+class TestLaunchBrokerAndHostControllerDomains(unittest.TestCase):
+    """The real #468 domains: the launch-broker key (shared by orchestrator +
+    host controller) and the host controller's own lifecycle key."""
+
+    def test_launch_broker_mints_no_role_tokens(self) -> None:
+        # Empty role set — it provides durable key material for the broker's own
+        # launch JWT, not orchestrator_auth role tokens.
+        self.assertEqual(frozenset(), LAUNCH_BROKER.roles)
+        with patch("bot_bottle.trust_domain.host_signing_key", return_value="k"):
+            with self.assertRaises(ValueError):
+                LAUNCH_BROKER.mint(ROLE_CLI)
+
+    def test_host_controller_signs_host_role_only(self) -> None:
+        with patch("bot_bottle.trust_domain.host_signing_key", return_value="k"):
+            tok = HOST_CONTROLLER.mint(ROLE_HOST)
+        self.assertEqual(ROLE_HOST, HOST_CONTROLLER.verify(tok, "k"))
+        # A control-plane `cli` token (the orchestrator's key) never verifies as a
+        # host-controller role — the orchestrator can't forge lifecycle creds.
+        cli_tok = orchestrator_auth.mint(ROLE_CLI, "k")
+        self.assertIsNone(HOST_CONTROLLER.verify(cli_tok, "k"))
+
+    def test_control_plane_cannot_mint_the_host_role(self) -> None:
+        # `host` is outside the control-plane role set on purpose.
+        with patch("bot_bottle.trust_domain.host_signing_key", return_value="k"):
+            with self.assertRaises(ValueError):
+                CONTROL_PLANE.mint(ROLE_HOST)
+
+    def test_the_three_domains_use_distinct_keys_and_env_vars(self) -> None:
+        self.assertEqual(3, len({
+            CONTROL_PLANE.key_filename,
+            LAUNCH_BROKER.key_filename,
+            HOST_CONTROLLER.key_filename,
+        }))
+        self.assertEqual(3, len({
+            CONTROL_PLANE.key_env, LAUNCH_BROKER.key_env, HOST_CONTROLLER.key_env,
+        }))
+
+
+class TestLaunchBrokerProvisioning(unittest.TestCase):
+    def test_broker_key_returns_the_durable_key(self) -> None:
+        prov = LaunchBrokerProvisioning()
+        with patch("bot_bottle.trust_domain.host_signing_key", return_value="bk"):
+            self.assertEqual("bk", prov.broker_key())
+
+    def test_broker_key_fail_closes_when_empty(self) -> None:
+        # An empty key would leave the host controller unable to verify any
+        # launch — fail-closed rather than hand back a useless/dangerous key.
+        prov = LaunchBrokerProvisioning()
+        with patch("bot_bottle.trust_domain.host_signing_key", return_value=""):
+            with self.assertRaises(ProvisioningError):
+                prov.broker_key()
+
+    def test_controller_key_is_distinct_from_the_broker_key(self) -> None:
+        # The orchestrator holds the broker key but NEVER the controller key.
+        prov = LaunchBrokerProvisioning()
+        keys = {"launch-broker-key": "bk", "host-controller-key": "ck"}
+        with patch("bot_bottle.trust_domain.host_signing_key",
+                   side_effect=keys.__getitem__):
+            self.assertEqual("bk", prov.broker_key())
+            self.assertEqual("ck", prov.controller_key())
+
+    def test_controller_key_fail_closes_when_empty(self) -> None:
+        prov = LaunchBrokerProvisioning()
+        with patch("bot_bottle.trust_domain.host_signing_key", return_value=""):
+            with self.assertRaises(ProvisioningError):
+                prov.controller_key()
+
+
 if __name__ == "__main__":
     unittest.main()