Reduce turn latency: cap recent events (10→5) + concise-reasoning constraint (v0.9.0)

Fixes #22

server/engine.test.ts

@@ -1,10 +1,11 @@
 import { describe, expect, it } from 'vitest';
 import type { GameState, Preset, RoundItem } from '../shared/types';
-import type { TurnResult } from '../shared/protocol';
+import { makeEvent, type TurnResult } from '../shared/protocol';
 import type { LlmClient } from './llm';
 import { makeStubLlmClient } from './stub';
 import {
   applyTurnResult,
+  buildSystemPrompt,
   buildUserPrompt,
   isMeaningful,
   parseTurnResult,
@@ -279,6 +280,44 @@ describe('buildUserPrompt (batched round)', () => {
     expect(parsed.roundInstruction).toMatch(/no action/i);
     expect(parsed.roundInstruction).toMatch(/own momentum/i);
   });
+
+  it('caps recentEvents at the last 5 (in order) when the state has more than 5 events', () => {
+    const state = baseState();
+    const events = Array.from({ length: 8 }, (_, i) =>
+      makeEvent(
+        {
+          nation: 'uk',
+          type: 'political',
+          title: `Event ${i + 1}`,
+          text: `Narrative ${i + 1}`,
+          outcome: 'neutral',
+        },
+        i + 1,
+        `1939-09-0${i + 1}`,
+      ),
+    );
+    state.events = events;
+
+    const parsed = JSON.parse(buildUserPrompt(state, [])) as {
+      state: { recentEvents: Array<{ title: string; turn: number; date: string }> };
+    };
+
+    expect(parsed.state.recentEvents).toHaveLength(5);
+    // the last 5 of the 8 input events, in order
+    expect(parsed.state.recentEvents[0].title).toBe(events[3].title); // 'Event 4'
+    expect(parsed.state.recentEvents[4].title).toBe(events[7].title); // 'Event 8'
+    expect(parsed.state.recentEvents.map((e) => e.title)).toEqual([
+      events[3].title,
+      events[4].title,
+      events[5].title,
+      events[6].title,
+      events[7].title,
+    ]);
+  });
+
+  it('asks the model to keep its internal reasoning brief (concise-CoT constraint)', () => {
+    expect(buildSystemPrompt(preset)).toMatch(/reasoning brief|a few sentences/i);
+  });
 });
 
 describe('queueRoundItem', () => {