feat: add baseSystemPrompt

src/conversation.ts

@@ -20,14 +20,16 @@ export function formatMessageHistory(input: {
     .join("\n");
 }
 
-export function conversationInstruction(): string {
-  return [
+export function conversationInstruction(baseSystemPrompt?: string): string {
+  const parts = [
+    ...(baseSystemPrompt === undefined ? [] : [baseSystemPrompt]),
     "You are controlling the persona, not a generic assistant.",
     "Use the send_message tool conceptually: return one or more outgoing messages.",
     "Unless the persona strongly prefers otherwise, keep each outgoing message to at most one sentence.",
     "Prefer short, natural, chat-like wording and allow splitting one thought into multiple messages.",
     'If mandatory memory says "기억이 없음", the persona may naturally wonder about missing context instead of pretending to remember.',
-  ].join("\n");
+  ];
+  return parts.join("\n");
 }
 
 export async function buildMandatoryConversationContext(input: {

src/persona.ts

@@ -68,6 +68,7 @@ export class Persona {
   private readonly mode: Mode;
   private readonly readyPromise: Promise<MemorySpace>;
   private availabilitySnapshot?: ScheduledAvailabilitySnapshot;
+  readonly baseSystemPrompt: string | undefined;
 
   constructor(
     displayName: string,
@@ -88,6 +89,7 @@ export class Persona {
       this.options = second ?? {};
     }
     this.memory = this.options.memory ?? new InMemoryMemoryStore();
+    this.baseSystemPrompt = this.options.baseSystemPrompt;
     this.readyPromise = this.initialize();
   }
 
@@ -247,7 +249,7 @@ export class Persona {
         mode: "reply",
         context,
         ...(userMessage === undefined ? {} : { userMessage }),
-        instruction: conversationInstruction(),
+        instruction: conversationInstruction(this.baseSystemPrompt),
       }),
     );
 
@@ -281,7 +283,7 @@ export class Persona {
                 now: toIso(input.datetime),
                 mode: "reply",
                 context: latestContext,
-                instruction: conversationInstruction(),
+                instruction: conversationInstruction(this.baseSystemPrompt),
               })),
           );
         }
@@ -320,7 +322,7 @@ export class Persona {
         now: toIso(input.datetime),
         mode: "start-conversation",
         context,
-        instruction: conversationInstruction(),
+        instruction: conversationInstruction(this.baseSystemPrompt),
       }),
     );
     await this.emit("persona.conversation.started", {

src/types.ts

@@ -160,6 +160,7 @@ export interface PersonaOptions {
   models?: PersonaModels;
   debug?: DebugHook;
   now?: DateTimeInput;
+  baseSystemPrompt?: string;
 }
 
 export interface BoxBrainMemoryStore {

tests/conversation.test.ts

@@ -124,4 +124,30 @@ describe('Conversation API', () => {
     expect(mode).toBe('start-conversation');
     expect(started.messages).toEqual(['오늘 좀 조용하네.']);
   });
+
+  it('includes baseSystemPrompt at the start of the instruction when provided', async () => {
+    const memory = new InMemoryMemoryStore();
+    let captured: ReplyGenerationInput | undefined;
+    const persona = new Persona('Mina', 'Mina likes quiet cafes.', {
+      memory,
+      now: '2026-05-01T10:00:00.000Z',
+      baseSystemPrompt: 'You are a helpful assistant. Always be kind.',
+      models: {
+        conversation: {
+          async generateReply(input) {
+            captured = input;
+            return { messages: ['Hello!'] };
+          },
+        },
+      },
+    });
+    await persona.ready();
+
+    await persona.sendMessage({
+      datetime: '2026-05-01T12:00:00.000Z',
+      messageHistory: [{ sender: 'user', time: '2026-05-01T12:00:00.000Z', content: 'Hi' }],
+    });
+
+    expect(captured?.instruction.startsWith('You are a helpful assistant. Always be kind.')).toBe(true);
+  });
 });

tests/persona.test.ts

@@ -29,6 +29,18 @@ describe('Persona initialization', () => {
     expect(debug).toContain('persona.initialized');
   });
 
+  it('exposes baseSystemPrompt on the persona instance when provided', async () => {
+    const memory = new InMemoryMemoryStore();
+    const persona = new Persona('Hana', 'Hana is a cheerful barista.', {
+      memory,
+      now: '2026-05-01T10:00:00.000Z',
+      baseSystemPrompt: 'You are a helpful assistant. Always be kind.',
+    });
+
+    await persona.ready();
+    expect(persona.baseSystemPrompt).toBe('You are a helpful assistant. Always be kind.');
+  });
+
   it('loads an existing persona space by space id without creating another space', async () => {
     const memory = new InMemoryMemoryStore();
     const created = new Persona('Joon', 'Joon is a freelance designer.', { memory, now: '2026-05-01T10:00:00.000Z' });