feat: add LogService with ring buffer and subscriber push

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/services/__tests__/logService.test.ts

@@ -0,0 +1,40 @@
+import { describe, it, expect, beforeEach } from 'vitest';
+import { createLogService } from '../logService.js';
+
+describe('LogService', () => {
+  let logService: ReturnType<typeof createLogService>;
+
+  beforeEach(() => {
+    logService = createLogService();
+  });
+
+  it('logs entries and returns them via getRecent', () => {
+    logService.log('info', 'Game', 'Server started');
+    const entries = logService.getRecent();
+    expect(entries).toHaveLength(1);
+    expect(entries[0].severity).toBe('info');
+    expect(entries[0].category).toBe('Game');
+    expect(entries[0].message).toBe('Server started');
+    expect(entries[0].timestamp).toBeGreaterThan(0);
+  });
+
+  it('enforces ring buffer limit of 200', () => {
+    for (let i = 0; i < 210; i++) {
+      logService.log('info', 'Game', `Entry ${i}`);
+    }
+    const entries = logService.getRecent();
+    expect(entries).toHaveLength(200);
+    expect(entries[0].message).toBe('Entry 10');
+  });
+
+  it('notifies subscribers on new entry', () => {
+    const received: any[] = [];
+    const unsub = logService.subscribe((entry) => received.push(entry));
+    logService.log('error', 'LLM', 'Timeout');
+    expect(received).toHaveLength(1);
+    expect(received[0].severity).toBe('error');
+    unsub();
+    logService.log('info', 'Game', 'Ignored');
+    expect(received).toHaveLength(1);
+  });
+});

server/src/services/logService.ts

@@ -0,0 +1,37 @@
+import type { LogEntry, LogSeverity, LogCategory } from '@dflike/shared';
+
+const MAX_ENTRIES = 200;
+
+export function createLogService() {
+  const entries: LogEntry[] = [];
+  const subscribers = new Set<(entry: LogEntry) => void>();
+
+  return {
+    log(severity: LogSeverity, category: LogCategory, message: string): void {
+      const entry: LogEntry = {
+        timestamp: Date.now(),
+        severity,
+        category,
+        message,
+      };
+      entries.push(entry);
+      if (entries.length > MAX_ENTRIES) {
+        entries.shift();
+      }
+      for (const cb of subscribers) {
+        cb(entry);
+      }
+    },
+
+    getRecent(): LogEntry[] {
+      return [...entries];
+    },
+
+    subscribe(cb: (entry: LogEntry) => void): () => void {
+      subscribers.add(cb);
+      return () => { subscribers.delete(cb); };
+    },
+  };
+}
+
+export type LogService = ReturnType<typeof createLogService>;