feat(memory): build session context for getSystemPrompt

src/backends/native/orchestrator.ts

@@ -574,6 +574,7 @@ export class AgentOrchestrator {
    */
   getSystemPrompt(userMessage?: string): string {
     if (typeof userMessage === 'string') {
+      this._buildSessionContext();
       this._injectMemoryContext(userMessage);
     }
     return this._agent.getSystemPrompt();