feat(sessions): add agent-to-agent post step

src/gateway/protocol/schema.ts

@@ -209,6 +209,7 @@ export const AgentParamsSchema = Type.Object(
     channel: Type.Optional(Type.String()),
     timeout: Type.Optional(Type.Integer({ minimum: 0 })),
     lane: Type.Optional(Type.String()),
+    extraSystemPrompt: Type.Optional(Type.String()),
     idempotencyKey: NonEmptyString,
   },
   { additionalProperties: false },

src/gateway/server-methods.ts

@@ -2931,6 +2931,7 @@ export async function handleGatewayRequest(
         deliver?: boolean;
         channel?: string;
         lane?: string;
+        extraSystemPrompt?: string;
         idempotencyKey: string;
         timeout?: number;
       };
@@ -3122,6 +3123,7 @@ export async function handleGatewayRequest(
           surface: "VoiceWake",
           runId,
           lane: params.lane,
+          extraSystemPrompt: params.extraSystemPrompt,
         },
         defaultRuntime,
         deps,