/**
 * Per-instance idempotency guard for extension activation.
 *
 * pix-core (the meta-package) invokes this package's factory, and a standalone
 * install makes Pi invoke it again — sometimes against the SAME `pi`. We must
 * dedupe that. But Pi rebuilds the extension runtime on /new, /resume, /fork,
 * and /reload, handing the factory a BRAND-NEW `pi`; that must re-register.
 *
 * Keying the registry on the `pi` instance satisfies both: same instance =>
 * skip, new instance => run. The registry lives on globalThis because jiti
 * (`moduleCache: false`) re-evaluates this module on every load pass, so a
 * module-scoped WeakMap would not be shared between the aggregator pass and the
 * standalone pass within a single session.
 */
export function once(pi: object, key: string, fn: () => void): void {
	const g = globalThis as { __pixOnce?: WeakMap<object, Set<string>> };
	if (!g.__pixOnce) g.__pixOnce = new WeakMap<object, Set<string>>();
	const registry = g.__pixOnce;
	let loaded = registry.get(pi);
	if (!loaded) {
		loaded = new Set<string>();
		registry.set(pi, loaded);
	}
	if (loaded.has(key)) return;
	loaded.add(key);
	fn();
}