fix(security): authenticate the orchestrator control plane (issue #400 Critical)

The control plane had no caller authentication — dispatch() routed every
request straight through, and the only guards anywhere were the
(source_ip, identity_token) checks inside /resolve and /attribute, which
authenticate the *bottle* a request is about, not the *caller*. On the
consolidated backends the agent shares a network with the control-plane port
(macOS: the infra container runs 8099 on the agent's --internal network;
docker: the orchestrator container sits on the shared gateway network), so a
prompt-injected agent could GET /bottles (enumerate siblings + policies),
PUT /bottles/<id>/policy (rewrite its own egress allowlist to allow-all),
POST /resolve (read the injected upstream credentials it's never meant to
see), and POST /supervise/respond (self-approve its own proposals). Every
README guarantee collapsed to the agent's discretion.

Fix: a per-host control-plane secret required on every route but GET /health,
compared with hmac.compare_digest. It is held only by the trusted callers and
never handed to an agent:
- minted + persisted 0600 at <root>/control-plane-token (paths.host_control_plane_token);
- injected as $BOT_BOTTLE_CONTROL_PLANE_TOKEN into the orchestrator + gateway
  containers via bare `--env NAME` (value inherited from the launch process,
  so it never lands on argv or in `container/docker inspect`);
- presented by the gateway's PolicyResolver (reads the env) on /resolve, and by
  the host CLI's OrchestratorClient (reads the host file) on every call.

The agent container is never given the env var or the host file, so from a
bottle every /bottles*, /resolve, /attribute, and /supervise/* call now
returns 401 — closing the enumeration, allowlist-rewrite, credential-lift, and
self-approval. The existing (source_ip, identity_token) checks stay as
defense-in-depth.

Enforced when configured: macOS + docker inject the secret (→ enforced). With
no secret set the server runs open and warns loudly at startup — a
fail-visible fallback for the unit suite and for Firecracker, whose
port-scoped nft already blocks agents from 8099 (wiring the secret into its
infra-VM init is a clean fast-follow, left out here to avoid churning the
prebuilt-artifact hash).

Verified end-to-end on real Apple Container: infra comes up healthy, the host
CLI (with the secret) lists bottles while an unauthenticated GET /bottles gets
401, all five issue-#400 attacks from inside the agent get 401, and egress
policy still works (200 allowed / 403 denied) — proving the gateway
authenticates to /resolve with the secret. 1829 unit tests pass, pyright
clean, pylint 9.91.

Refs #400.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

bot_bottle/policy_resolver.py

@@ -29,11 +29,29 @@ the gateway.
 from __future__ import annotations
 
 import json
+import os
 import urllib.error
 import urllib.request
 
 DEFAULT_TIMEOUT_SECONDS = 2.0
 
+# The control-plane secret this gateway presents on every /resolve call, read
+# from the env the launcher injects into the gateway container. The control
+# plane requires it (orchestrator/control_plane.py). Constant + env-var name are
+# duplicated here rather than imported because this module is COPYed flat into
+# the gateway image, free of bot-bottle imports — same rationale as
+# IDENTITY_HEADER in egress_addon / git_http_backend.
+CONTROL_AUTH_HEADER = "x-bot-bottle-control-auth"
+CONTROL_PLANE_TOKEN_ENV = "BOT_BOTTLE_CONTROL_PLANE_TOKEN"
+
+
+def _control_auth_headers() -> dict[str, str]:
+    """The auth header to send, or {} when no secret is configured (an open
+    control plane, e.g. Firecracker behind its nft boundary — sending nothing
+    is correct there and harmlessly ignored)."""
+    token = os.environ.get(CONTROL_PLANE_TOKEN_ENV, "").strip()
+    return {CONTROL_AUTH_HEADER: token} if token else {}
+
 
 class PolicyResolveError(RuntimeError):
     """The orchestrator was unreachable or returned an unexpected status —
@@ -57,7 +75,7 @@ class PolicyResolver:
         ).encode()
         req = urllib.request.Request(
             f"{self._base}/resolve", data=body, method="POST",
-            headers={"Content-Type": "application/json"},
+            headers={"Content-Type": "application/json", **_control_auth_headers()},
         )
         try:
             with urllib.request.urlopen(req, timeout=self._timeout) as resp: