Add authenticated broker contract

backend/cortex_backend/execution/__init__.py

@@ -1,9 +1,25 @@
-"""Phase 1 durable execution primitives.
+"""Durable execution primitives and provider-independent safety contracts.
 
-Only the deterministic fake provider is exposed in this phase. Real runtime
-providers are intentionally absent until later ADR gates are approved.
+Only the deterministic fake provider and transport-neutral broker contract are
+exposed in this phase. Native transports and real runtime providers remain absent
+until later ADR gates are approved.
 """
 
+from .broker import (
+    BrokerAclPolicy,
+    BrokerFrame,
+    BrokerFrameDecoder,
+    BrokerMessage,
+    BrokerPeerPolicy,
+    BrokerProtocolError,
+    BrokerSessionKeys,
+    PeerIdentity,
+    authorize_message,
+    decode_frame,
+    decode_message,
+    encode_frame,
+    encode_message,
+)
 from .fake import FakeExecutionPlan, FakeExecutionProvider
 from .lifecycle import ExecutionLifecycle, LifecycleSnapshot, RuntimeHealth
 from .manifest import (
@@ -42,6 +58,13 @@
     "ArtifactLimitError",
     "ApprovalPolicyError",
     "ApprovalTransitionError",
+    "BrokerAclPolicy",
+    "BrokerFrame",
+    "BrokerFrameDecoder",
+    "BrokerMessage",
+    "BrokerPeerPolicy",
+    "BrokerProtocolError",
+    "BrokerSessionKeys",
     "ExecutionRepository",
     "ExecutionRepositoryError",
     "ExecutionLifecycle",
@@ -69,4 +92,10 @@
     "parse_image_transform",
     "verify_bundle_files",
     "verify_signed_manifest",
+    "PeerIdentity",
+    "authorize_message",
+    "decode_frame",
+    "decode_message",
+    "encode_frame",
+    "encode_message",
 ]