Invalidate a server cache the instant a config flips

You memoize an expensive render — a navigation tree, a pricing table, a derived config object — and key it off a flag or dynamic config. It's fast, but now it's stale: someone flips the config in the dashboard and your long-lived server keeps serving the cached version until the next deploy. Flag reads are fresh on every poll; your derived cache isn't.

onChange closes the gap: it fires the moment a background poll picks up new rules, so you can drop the derived cache exactly when — and only when — something actually changed.

import { Engine } from "@shipeasy/sdk/server";

const engine = new Engine({ apiKey: process.env.SHIPEASY_SERVER_KEY! });
await engine.init();

const unsubscribe = engine.onChange(() => {
  rebuildRenderCache(); // drop the memoized render / derived config
});

// on shutdown
unsubscribe();

In the browser the equivalent is engine.subscribe(), which fires after each identify() and after any override change — exactly when a re-render is warranted:

import { Engine } from "@shipeasy/sdk/client";

const engine = new Engine({ clientKey: process.env.NEXT_PUBLIC_SHIPEASY_CLIENT_KEY! });

const unsubscribe = engine.subscribe(() => {
  renderFlags();
});

Rollout & measurement plan

• Invalidate, don't poll your cache. Don't re-derive on every request "just in case" — subscribe once and rebuild only on the change event.
• Latency is the poll interval. A config flip lands within one poll (30s on Free, 60s on Team), not instantly — that's the freshness contract, and it's plenty for cache busting.
• Serverless has nothing to subscribe to. A one-shot request reads the latest blob and exits; onChange is for long-lived servers, background jobs, and live dashboards.