diff --git a/packages/contracts/src/message-metadata.ts b/packages/contracts/src/message-metadata.ts
index 5c767ed..e92a458 100644
--- a/packages/contracts/src/message-metadata.ts
+++ b/packages/contracts/src/message-metadata.ts
@@ -33,6 +33,11 @@ export type MessageMetadata =
       kind: 'error';
       error_reason: ErrorReason;
       error_text: string;
+    }
+  | {
+      kind: 'feedback';
+      value: 'up' | 'down';
+      chat_id: string;
     };
 
 // Unified definition is the web required/nullable shape (the coder's all-optional
diff --git a/packages/contracts/src/ws-frames.ts b/packages/contracts/src/ws-frames.ts
index 832cabc..153cd6d 100644
--- a/packages/contracts/src/ws-frames.ts
+++ b/packages/contracts/src/ws-frames.ts
@@ -369,6 +369,19 @@ export const FlowRunStepUpdatedFrame = z.object({
   report: z.string().optional(),
 });
 
+// ---- inter-agent message frame ---------------------------------------------
+//
+// Published when one agent step sends a live message to another step in the
+// same flow run. Broadcast on the user WS channel and delivered to in-process
+// subscribers via the broker's internal topic.
+export const AgentMessageFrame = z.object({
+  type: z.literal('agent_message'),
+  run_id: Uuid,
+  sender_step_id: z.string().min(1),
+  content: z.string(),
+  channel: z.string().optional(),
+});
+
 // ---- arena frames ----------------------------------------------------------
 
 const ContestantManifestEntry = z.object({
@@ -583,6 +596,8 @@ export const WsFrameSchema = z.discriminatedUnion('type', [
   CollisionWarningFrame,
   // channel-delta (streaming v2)
   ChannelDeltaFrame,
+  // inter-agent message
+  AgentMessageFrame,
   // per-user
   ChatStatusFrame,
   SessionUpdatedFrame,
@@ -635,6 +650,7 @@ export const KNOWN_FRAME_TYPES: readonly WsFrame['type'][] = [
   'tool_trace_finish',
   'collision_warning',
   'channel_delta',
+  'agent_message',
   'chat_status',
   'session_updated',
   'session_renamed',