feat: configurable heartbeat session

src/config/types.agent-defaults.ts

@@ -173,6 +173,8 @@ export type AgentDefaultsConfig = {
     };
     /** Heartbeat model override (provider/model). */
     model?: string;
+    /** Session key for heartbeat runs ("main" or explicit session key). */
+    session?: string;
     /** Delivery target (last|whatsapp|telegram|discord|slack|msteams|signal|imessage|none). */
     target?:
       | "last"

src/config/zod-schema.agent-runtime.ts

@@ -20,6 +20,7 @@ export const HeartbeatSchema = z
       .strict()
       .optional(),
     model: z.string().optional(),
+    session: z.string().optional(),
     includeReasoning: z.boolean().optional(),
     target: z
       .union([