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 (re-adoption). HOST_CONTROLLER is the separate
  domain for the controller's own lifecycle endpoints, keyed by a key the
  orchestrator never holds (its lifecycle role is `host`, deliberately
  outside the control-plane ROLES). LaunchBrokerProvisioning is the
  fail-closed seam, mirroring ControlPlaneProvisioning.
- orchestrator_auth.py: ROLE_HOST, outside ROLES so the orchestrator's
  control-plane key can neither mint nor accept it.
- paths.py: key-file + env-var constants for both domains.
- host_server.py / __main__.py: broker_secret() now resolves the durable
  LAUNCH_BROKER key — env-injected for a containerized launcher, else the
  host key file for a host-side dev-harness process — so `--broker http`
  and the host controller "just work" on one host without exporting a
  secret, and stay fail-closed when the root is unwritable.

Tested: domain boundary (host role unmintable by the control plane,
cross-domain tokens don't verify), distinct keys/env vars per domain,
provisioning fail-closed, and broker_secret env/file resolution +
durability. Full unit suite green; pyright clean; pylint 9.90.

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

bot_bottle/paths.py

@@ -47,6 +47,22 @@ ORCHESTRATOR_TOKEN_ENV = "BOT_BOTTLE_ORCHESTRATOR_TOKEN"
 # cannot forge a higher-privilege `cli` token (issue #469 review).
 ORCHESTRATOR_AUTH_JWT_ENV = "BOT_BOTTLE_ORCHESTRATOR_AUTH_JWT"
 
+# The durable launch-broker signing key: the HS256 secret the orchestrator
+# (signer) and the host control server (verifier) share to sign/verify launch
+# requests (#468). A host-canonical key file (minted 0600 on first use) so it
+# survives orchestrator restarts — re-adoption re-verifies against the same key —
+# instead of the ephemeral per-process secret of the in-process broker.
+LAUNCH_BROKER_KEY_FILENAME = "launch-broker-key"
+LAUNCH_BROKER_KEY_ENV = "BOT_BOTTLE_LAUNCH_BROKER_KEY"
+# The host controller's OWN key, for its lifecycle endpoints (the direct
+# cli -> host controller path that starts/stops the orchestrator). Separate from
+# the launch-broker key and never held by the orchestrator: the controller starts
+# and stops the orchestrator, so the orchestrator must not be able to mint the
+# credentials used to drive it (#468/#476).
+HOST_CONTROLLER_KEY_FILENAME = "host-controller-key"
+HOST_CONTROLLER_KEY_ENV = "BOT_BOTTLE_HOST_CONTROLLER_KEY"
+HOST_CONTROLLER_AUTH_JWT_ENV = "BOT_BOTTLE_HOST_CONTROLLER_AUTH_JWT"
+
 # The host directory holding the gateway's persistent mitmproxy CA. Bind-mounted
 # into the infra/gateway container at mitmproxy's confdir so the self-generated
 # CA survives container recreation — every agent installs this one CA to trust
@@ -142,6 +158,11 @@ __all__ = [
     "ORCHESTRATOR_TOKEN_FILENAME",
     "ORCHESTRATOR_TOKEN_ENV",
     "ORCHESTRATOR_AUTH_JWT_ENV",
+    "LAUNCH_BROKER_KEY_FILENAME",
+    "LAUNCH_BROKER_KEY_ENV",
+    "HOST_CONTROLLER_KEY_FILENAME",
+    "HOST_CONTROLLER_KEY_ENV",
+    "HOST_CONTROLLER_AUTH_JWT_ENV",
     "GATEWAY_CA_DIRNAME",
     "bot_bottle_root",
     "host_db_path",