feat: add baseSystemPrompt

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);
+  });
 });