diff --git a/package-lock.json b/package-lock.json
index f206cc1..c4b0600 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -3843,6 +3843,20 @@
         }
       }
     },
+    "node_modules/html-encoding-sniffer/node_modules/@noble/hashes": {
+      "version": "2.3.0",
+      "resolved": "https://registry.npmjs.org/@noble/hashes/-/hashes-2.3.0.tgz",
+      "integrity": "sha512-oN+QwyX7VSHotibwubG3kpzbwKrfnyR6OOO+3Nk/53ADL7FmgHHz4TgrbaYKvvOw09u6QTx0oiH1cNCIOuN0CQ==",
+      "dev": true,
+      "optional": true,
+      "peer": true,
+      "engines": {
+        "node": ">= 20.19.0"
+      },
+      "funding": {
+        "url": "https://paulmillr.com/funding/"
+      }
+    },
     "node_modules/https-proxy-agent": {
       "version": "5.0.1",
       "license": "MIT",
@@ -4041,6 +4055,20 @@
         }
       }
     },
+    "node_modules/jsdom/node_modules/@noble/hashes": {
+      "version": "2.3.0",
+      "resolved": "https://registry.npmjs.org/@noble/hashes/-/hashes-2.3.0.tgz",
+      "integrity": "sha512-oN+QwyX7VSHotibwubG3kpzbwKrfnyR6OOO+3Nk/53ADL7FmgHHz4TgrbaYKvvOw09u6QTx0oiH1cNCIOuN0CQ==",
+      "dev": true,
+      "optional": true,
+      "peer": true,
+      "engines": {
+        "node": ">= 20.19.0"
+      },
+      "funding": {
+        "url": "https://paulmillr.com/funding/"
+      }
+    },
     "node_modules/json-schema-traverse": {
       "version": "1.0.0",
       "resolved": "https://registry.npmjs.org/json-schema-traverse/-/json-schema-traverse-1.0.0.tgz",
@@ -6690,6 +6718,20 @@
         }
       }
     },
+    "node_modules/whatwg-url/node_modules/@noble/hashes": {
+      "version": "2.3.0",
+      "resolved": "https://registry.npmjs.org/@noble/hashes/-/hashes-2.3.0.tgz",
+      "integrity": "sha512-oN+QwyX7VSHotibwubG3kpzbwKrfnyR6OOO+3Nk/53ADL7FmgHHz4TgrbaYKvvOw09u6QTx0oiH1cNCIOuN0CQ==",
+      "dev": true,
+      "optional": true,
+      "peer": true,
+      "engines": {
+        "node": ">= 20.19.0"
+      },
+      "funding": {
+        "url": "https://paulmillr.com/funding/"
+      }
+    },
     "node_modules/which": {
       "version": "2.0.2",
       "dev": true,
diff --git a/src/cache.ts b/src/cache.ts
index e63e455..72ccb52 100644
--- a/src/cache.ts
+++ b/src/cache.ts
@@ -141,3 +141,107 @@ export class SimpleCache<T> {
     }
   }
 }
+
+/**
+ * A lightweight, generic in-memory cache with optional TTL-based entry expiry.
+ *
+ * When `ttlMs` is omitted entries never expire, preserving backward-compatible
+ * behaviour.  When supplied, `get()` and `has()` silently evict stale entries
+ * on access, and `purgeExpired()` sweeps the entire store in one pass.
+ *
+ * Usage:
+ *   const cache = new Cache<Invoice>(30_000); // 30-second TTL
+ *   cache.set("inv:1", invoice);
+ *   cache.get("inv:1"); // undefined after 30 s
+ */
+interface CacheEntry<V> {
+  value: V;
+  /** Unix ms timestamp recorded at write time. */
+  writtenAt: number;
+}
+
+export class Cache<V> {
+  private readonly store = new Map<string, CacheEntry<V>>();
+  private readonly ttlMs: number | undefined;
+
+  /**
+   * @param ttlMs  Time-to-live in milliseconds.  Omit (or pass `undefined`)
+   *               for no-expiry behaviour.
+   */
+  constructor(ttlMs?: number) {
+    this.ttlMs = ttlMs;
+  }
+
+  /**
+   * Store `value` under `key`, recording the current wall-clock time.
+   */
+  set(key: string, value: V): void {
+    this.store.set(key, { value, writtenAt: Date.now() });
+  }
+
+  /**
+   * Retrieve the value for `key`.
+   *
+   * Returns `undefined` and **deletes the entry** when the entry is expired
+   * (i.e. `Date.now() - writtenAt > ttlMs`).  Returns `undefined` for
+   * missing keys regardless of TTL configuration.
+   */
+  get(key: string): V | undefined {
+    const entry = this.store.get(key);
+    if (!entry) return undefined;
+    if (this.isExpired(entry)) {
+      this.store.delete(key);
+      return undefined;
+    }
+    return entry.value;
+  }
+
+  /**
+   * Returns `true` only when the key exists **and** is not expired.
+   * Expired entries are deleted as a side-effect.
+   */
+  has(key: string): boolean {
+    const entry = this.store.get(key);
+    if (!entry) return false;
+    if (this.isExpired(entry)) {
+      this.store.delete(key);
+      return false;
+    }
+    return true;
+  }
+
+  /**
+   * Remove all entries whose TTL has elapsed in a single sweep.
+   * No-op when no TTL is configured.
+   */
+  purgeExpired(): void {
+    if (this.ttlMs === undefined) return;
+    for (const [key, entry] of this.store) {
+      if (this.isExpired(entry)) {
+        this.store.delete(key);
+      }
+    }
+  }
+
+  /** Remove a specific entry by key. */
+  delete(key: string): void {
+    this.store.delete(key);
+  }
+
+  /** Remove all entries. */
+  clear(): void {
+    this.store.clear();
+  }
+
+  /** Number of entries currently in the store (including not-yet-evicted expired ones). */
+  get size(): number {
+    return this.store.size;
+  }
+
+  // ── private helpers ──────────────────────────────────────────────────────
+
+  private isExpired(entry: CacheEntry<V>): boolean {
+    if (this.ttlMs === undefined) return false;
+    return Date.now() - entry.writtenAt > this.ttlMs;
+  }
+}
diff --git a/src/index.ts b/src/index.ts
index 2fe2b4a..d3438cd 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -379,7 +379,7 @@ export type { PathQuery, PathQueryResult, StrictSendPathQuery, StrictReceivePath
 export { OfferTracker } from "./offerTracker.js";
 export type { OfferTrackerConfig, OfferTrackerEventMap } from "./offerTracker.js";
 
-export { SimpleCache } from "./cache.js";
+export { SimpleCache, Cache } from "./cache.js";
 export { Recorder, createRecorder } from "./recorder.js";
 export type { SessionRecording, RecordingEntry, ReplayResult } from "./recorder.js";
 
diff --git a/test/cache.test.ts b/test/cache.test.ts
index 839ed90..ff0872f 100644
--- a/test/cache.test.ts
+++ b/test/cache.test.ts
@@ -1,5 +1,5 @@
-import { describe, it, expect, vi } from "vitest";
-import { SimpleCache } from "../src/cache.js";
+import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
+import { SimpleCache, Cache } from "../src/cache.js";
 
 describe("SimpleCache LRU", () => {
   it("evicts the oldest entry when maxEntries is exceeded", () => {
@@ -71,3 +71,154 @@ describe("SimpleCache LRU", () => {
     expect(stats.evictions).toBe(0);
   });
 });
+
+describe("Cache – TTL-based expiry", () => {
+  beforeEach(() => {
+    vi.useFakeTimers();
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  // ── construction ──────────────────────────────────────────────────────────
+
+  it("accepts an optional ttlMs constructor argument", () => {
+    const withTtl = new Cache<string>(1000);
+    const withoutTtl = new Cache<string>();
+    expect(withTtl).toBeDefined();
+    expect(withoutTtl).toBeDefined();
+  });
+
+  // ── set / get ─────────────────────────────────────────────────────────────
+
+  it("get() returns the value before TTL elapses", () => {
+    const cache = new Cache<string>(1000);
+    cache.set("key", "value");
+    vi.advanceTimersByTime(999);
+    expect(cache.get("key")).toBe("value");
+  });
+
+  it("get() returns undefined and removes the entry after TTL elapses", () => {
+    const cache = new Cache<string>(1000);
+    cache.set("key", "value");
+    vi.advanceTimersByTime(1001);
+    expect(cache.get("key")).toBeUndefined();
+    // Entry must have been deleted
+    expect(cache.size).toBe(0);
+  });
+
+  it("get() returns undefined for a missing key", () => {
+    const cache = new Cache<string>(1000);
+    expect(cache.get("nonexistent")).toBeUndefined();
+  });
+
+  it("records the write timestamp at the moment of set()", () => {
+    const cache = new Cache<number>(500);
+    vi.advanceTimersByTime(200);
+    cache.set("k", 42); // written at t=200
+    vi.advanceTimersByTime(400); // now t=600; 400 ms after write > 500 ms TTL? no: 400 < 500
+    expect(cache.get("k")).toBe(42);
+    vi.advanceTimersByTime(101); // now t=701; 501 ms after write — expired
+    expect(cache.get("k")).toBeUndefined();
+  });
+
+  // ── has() ─────────────────────────────────────────────────────────────────
+
+  it("has() returns true for an entry that has not expired", () => {
+    const cache = new Cache<string>(1000);
+    cache.set("key", "value");
+    vi.advanceTimersByTime(500);
+    expect(cache.has("key")).toBe(true);
+  });
+
+  it("has() returns false for an expired entry and removes it", () => {
+    const cache = new Cache<string>(1000);
+    cache.set("key", "value");
+    vi.advanceTimersByTime(1001);
+    expect(cache.has("key")).toBe(false);
+    expect(cache.size).toBe(0);
+  });
+
+  it("has() returns false for a missing key", () => {
+    const cache = new Cache<string>(1000);
+    expect(cache.has("ghost")).toBe(false);
+  });
+
+  // ── purgeExpired() ────────────────────────────────────────────────────────
+
+  it("purgeExpired() removes only expired entries", () => {
+    const cache = new Cache<string>(1000);
+    cache.set("fresh", "a");
+    vi.advanceTimersByTime(500);
+    cache.set("also-fresh", "b");
+    vi.advanceTimersByTime(600); // "fresh" is now 1100 ms old (expired); "also-fresh" is 600 ms old (not expired)
+    cache.purgeExpired();
+    expect(cache.get("fresh")).toBeUndefined();
+    expect(cache.get("also-fresh")).toBe("b");
+    expect(cache.size).toBe(1);
+  });
+
+  it("purgeExpired() removes all entries when all are expired", () => {
+    const cache = new Cache<number>(500);
+    cache.set("a", 1);
+    cache.set("b", 2);
+    cache.set("c", 3);
+    vi.advanceTimersByTime(600);
+    cache.purgeExpired();
+    expect(cache.size).toBe(0);
+  });
+
+  it("purgeExpired() is a no-op when no TTL is configured", () => {
+    const cache = new Cache<string>(); // no TTL
+    cache.set("x", "1");
+    cache.set("y", "2");
+    vi.advanceTimersByTime(999999);
+    cache.purgeExpired();
+    // entries should still be present
+    expect(cache.get("x")).toBe("1");
+    expect(cache.get("y")).toBe("2");
+  });
+
+  // ── no-expiry (backward compatibility) ───────────────────────────────────
+
+  it("entries never expire when ttlMs is not provided", () => {
+    const cache = new Cache<string>();
+    cache.set("forever", "value");
+    vi.advanceTimersByTime(Number.MAX_SAFE_INTEGER / 2);
+    expect(cache.get("forever")).toBe("value");
+    expect(cache.has("forever")).toBe(true);
+  });
+
+  // ── delete / clear ────────────────────────────────────────────────────────
+
+  it("delete() removes a specific entry", () => {
+    const cache = new Cache<string>(5000);
+    cache.set("a", "1");
+    cache.set("b", "2");
+    cache.delete("a");
+    expect(cache.get("a")).toBeUndefined();
+    expect(cache.get("b")).toBe("2");
+  });
+
+  it("clear() removes all entries", () => {
+    const cache = new Cache<string>(5000);
+    cache.set("a", "1");
+    cache.set("b", "2");
+    cache.clear();
+    expect(cache.size).toBe(0);
+  });
+
+  // ── size ──────────────────────────────────────────────────────────────────
+
+  it("size reflects the number of stored entries", () => {
+    const cache = new Cache<number>(5000);
+    expect(cache.size).toBe(0);
+    cache.set("x", 1);
+    expect(cache.size).toBe(1);
+    cache.set("y", 2);
+    expect(cache.size).toBe(2);
+    cache.delete("x");
+    expect(cache.size).toBe(1);
+  });
+});