diff --git a/src/memory/workingMemory.test.ts b/src/memory/workingMemory.test.ts
new file mode 100644
index 0000000..f9749ea
--- /dev/null
+++ b/src/memory/workingMemory.test.ts
@@ -0,0 +1,76 @@
+import { describe, it, expect } from 'vitest';
+import { join } from 'path';
+import { mkdtempSync, rmSync } from 'fs';
+import { tmpdir } from 'os';
+import { MemoryStore } from './store.js';
+import { writeWorkingMemory, readWorkingMemory } from './workingMemory.js';
+
+function makeStore(): { store: MemoryStore; dir: string } {
+  const dir = mkdtempSync(join(tmpdir(), 'wm-test-'));
+  const store = new MemoryStore({ dir, maxContextTokens: 2000 });
+  return { store, dir };
+}
+
+describe('writeWorkingMemory', () => {
+  it('writes a file with Updated/Expires headers', () => {
+    const { store, dir } = makeStore();
+    writeWorkingMemory(store, 'user/working', 'some content', 14, 1000);
+    const raw = store.read('user/working');
+    expect(raw).toContain('# Working Memory');
+    expect(raw).toContain('Updated:');
+    expect(raw).toContain('Expires:');
+    expect(raw).toContain('some content');
+    rmSync(dir, { recursive: true });
+  });
+
+  it('truncates content to token budget', () => {
+    const { store, dir } = makeStore();
+    const longContent = 'x'.repeat(10000);
+    writeWorkingMemory(store, 'user/working', longContent, 14, 100);
+    const raw = store.read('user/working');
+    // 100 tokens * 4 chars = 400 chars budget for content
+    const contentPart = raw.split('\n\n').slice(1).join('\n\n');
+    expect(contentPart.length).toBeLessThanOrEqual(400 + 10); // small tolerance
+    rmSync(dir, { recursive: true });
+  });
+});
+
+describe('readWorkingMemory', () => {
+  it('returns null when file does not exist', () => {
+    const { store, dir } = makeStore();
+    expect(readWorkingMemory(store, 'user/working')).toBeNull();
+    rmSync(dir, { recursive: true });
+  });
+
+  it('returns content when not expired', () => {
+    const { store, dir } = makeStore();
+    writeWorkingMemory(store, 'user/working', 'hello world', 14, 1000);
+    const result = readWorkingMemory(store, 'user/working');
+    expect(result).not.toBeNull();
+    expect(result!.content).toBe('hello world');
+    rmSync(dir, { recursive: true });
+  });
+
+  it('returns null when expired', () => {
+    const { store, dir } = makeStore();
+    // Write a file with a hardcoded past expiry date for deterministic testing
+    const expiredFile = [
+      '# Working Memory',
+      'Updated: 2025-01-01T00:00:00Z',
+      'Expires: 2025-01-02T00:00:00Z',
+      '',
+      'stale content',
+    ].join('\n');
+    store.write('user/working', expiredFile, 'replace');
+    const result = readWorkingMemory(store, 'user/working');
+    expect(result).toBeNull();
+    rmSync(dir, { recursive: true });
+  });
+
+  it('returns null for malformed file', () => {
+    const { store, dir } = makeStore();
+    store.write('user/working', 'no headers here', 'replace');
+    expect(readWorkingMemory(store, 'user/working')).toBeNull();
+    rmSync(dir, { recursive: true });
+  });
+});
diff --git a/src/memory/workingMemory.ts b/src/memory/workingMemory.ts
new file mode 100644
index 0000000..665f660
--- /dev/null
+++ b/src/memory/workingMemory.ts
@@ -0,0 +1,86 @@
+import type { MemoryStore } from './store.js';
+
+export interface WorkingMemoryEntry {
+  content: string;
+  updatedAt: Date;
+  expiresAt: Date;
+}
+
+const HEADER_PREFIX = '# Working Memory\n';
+
+/**
+ * Write a compaction summary to the working memory namespace.
+ * Content is capped at maxTokens (estimated at 4 chars/token).
+ * The file format includes Updated/Expires timestamps for lazy expiry checks.
+ */
+export function writeWorkingMemory(
+  store: MemoryStore,
+  namespace: string,
+  content: string,
+  ttlDays: number,
+  maxTokens: number,
+): void {
+  const now = new Date();
+  const expiresAt = new Date(now.getTime() + ttlDays * 24 * 60 * 60 * 1000);
+  const maxChars = maxTokens * 4;
+  const truncatedContent = content.length > maxChars ? content.slice(0, maxChars) : content;
+
+  const file = [
+    '# Working Memory',
+    `Updated: ${now.toISOString()}`,
+    `Expires: ${expiresAt.toISOString()}`,
+    '',
+    truncatedContent,
+  ].join('\n');
+
+  store.write(namespace, file, 'replace');
+}
+
+/**
+ * Read working memory. Returns null if the file is absent, malformed, or expired.
+ * MemoryStore.read() returns '' for missing files, so falsy check works.
+ * Expiry is checked lazily here — no background cleanup needed.
+ */
+export function readWorkingMemory(
+  store: MemoryStore,
+  namespace: string,
+): WorkingMemoryEntry | null {
+  const raw = store.read(namespace);
+  if (!raw) {
+    return null;
+  }
+
+  if (!raw.startsWith(HEADER_PREFIX)) {
+    return null;
+  }
+
+  const lines = raw.split('\n');
+  let updatedAt: Date | null = null;
+  let expiresAt: Date | null = null;
+  let contentStartLine = 0;
+
+  for (let i = 1; i < lines.length; i++) {
+    const line = lines[i];
+    if (line.startsWith('Updated: ')) {
+      updatedAt = new Date(line.slice('Updated: '.length));
+    } else if (line.startsWith('Expires: ')) {
+      expiresAt = new Date(line.slice('Expires: '.length));
+    } else if (line === '' && expiresAt !== null) {
+      contentStartLine = i + 1;
+      break;
+    }
+  }
+
+  if (!updatedAt || !expiresAt || isNaN(expiresAt.getTime())) {
+    return null;
+  }
+
+  if (expiresAt.getTime() <= Date.now()) {
+    console.debug('[Flynn:working-memory] Working memory expired, skipping injection');
+    return null;
+  }
+
+  const content = lines.slice(contentStartLine).join('\n').trim();
+
+  return { content, updatedAt, expiresAt };
+}