diff --git a/src/arts/format/active-formats.svelte.ts b/src/arts/format/active-formats.svelte.ts
index 1be92bd..a020618 100644
--- a/src/arts/format/active-formats.svelte.ts
+++ b/src/arts/format/active-formats.svelte.ts
@@ -25,6 +25,13 @@ export interface ActiveFormat {
 	readonly dates: ActiveDates;
 	getLocale: () => string;
 	setLocale: (locale: string) => void;
+	/**
+	 * `true` once `dispose()` has been called. After dispose,
+	 * `setLocale()` is a silent no-op so a late event from a locale
+	 * source doesn't reach the already-disposed sub-engines.
+	 */
+	readonly disposed: boolean;
+	/** Idempotent. Disposes every sub-engine in stable order. */
 	dispose: () => void;
 }
 
@@ -36,8 +43,10 @@ export function createActiveFormat(options: ActiveFormatOptions = {}): ActiveFor
 	const currency = createActiveCurrency({ ...options.currency, localeSource, numbers });
 	const units = createActiveUnits({ ...options.units, localeSource, numbers });
 	const dates = createActiveDates({ ...options.dates, localeSource });
+	let disposed = false;
 
 	function setLocale(nextLocale: string): void {
+		if (disposed) return;
 		localeState.setLocale(nextLocale);
 		numbers.setLocale(nextLocale);
 		currency.setLocale(nextLocale);
@@ -52,7 +61,12 @@ export function createActiveFormat(options: ActiveFormatOptions = {}): ActiveFor
 		dates,
 		getLocale: () => numbers.getLocale(),
 		setLocale,
+		get disposed() {
+			return disposed;
+		},
 		dispose() {
+			if (disposed) return;
+			disposed = true;
 			numbers.dispose();
 			currency.dispose();
 			units.dispose();
diff --git a/src/arts/format/test/formats.test.ts b/src/arts/format/test/formats.test.ts
index bfe9bf9..d671ebc 100644
--- a/src/arts/format/test/formats.test.ts
+++ b/src/arts/format/test/formats.test.ts
@@ -45,4 +45,20 @@ describe('createActiveFormat()', () => {
 
 		formats.dispose();
 	});
+
+	it('exposes disposed flag, is idempotent, and ignores setLocale post-dispose', () => {
+		const formats = createActiveFormat({ locale: 'en-US' });
+
+		expect(formats.disposed).toBe(false);
+		formats.dispose();
+		expect(formats.disposed).toBe(true);
+
+		expect(() => formats.dispose()).not.toThrow();
+
+		// setLocale is a silent no-op after dispose; the cached values stay
+		// frozen at the last set value.
+		const lastLocale = formats.getLocale();
+		formats.setLocale('fr-FR');
+		expect(formats.getLocale()).toBe(lastLocale);
+	});
 });
diff --git a/src/arts/frontend/active-frontend.svelte.ts b/src/arts/frontend/active-frontend.svelte.ts
index 7f9070c..a92f7a7 100644
--- a/src/arts/frontend/active-frontend.svelte.ts
+++ b/src/arts/frontend/active-frontend.svelte.ts
@@ -63,6 +63,14 @@ export interface ActiveFrontend {
 	getDensity: () => FrontendDensity;
 	setDensity: (density: FrontendDensity) => void;
 	onPreferenceChange: (fn: () => void) => () => void;
+	/**
+	 * `true` once `dispose()` has been called. After dispose every
+	 * mutating setter is a silent no-op (so a UI tree being torn
+	 * down doesn't throw on a late event); read-only getters
+	 * continue to return the last applied value.
+	 */
+	readonly disposed: boolean;
+	/** Idempotent. Detaches media and locale subscriptions and clears listeners. */
 	dispose: () => void;
 }
 
@@ -127,6 +135,7 @@ export function createActiveFrontend(options: ActiveFrontendOptions = {}): Activ
 	}
 
 	function applyDom(): void {
+		if (disposed) return;
 		const target = resolveTarget(options.target);
 		if (dom === undefined || target === null) return;
 
@@ -143,12 +152,19 @@ export function createActiveFrontend(options: ActiveFrontendOptions = {}): Activ
 		});
 	}
 
+	/**
+	 * Drives every reactive setter. Guarded against post-dispose
+	 * activity so a late event from `localeSource` or a media query
+	 * teardown ordering quirk doesn't throw or rewrite the DOM.
+	 */
 	function notify(): void {
+		if (disposed) return;
 		applyDom();
 		for (const fn of listeners) fn();
 	}
 
 	function setLocale(locale: string): void {
+		if (disposed) return;
 		currentLocale = locale;
 		notify();
 	}
@@ -171,11 +187,13 @@ export function createActiveFrontend(options: ActiveFrontendOptions = {}): Activ
 
 		getDir,
 		setDir: (dir) => {
+			if (disposed) return;
 			dirOverride = dir === 'auto' ? null : dir;
 			notify();
 		},
 
 		clearDir: () => {
+			if (disposed) return;
 			dirOverride = null;
 			notify();
 		},
@@ -184,17 +202,20 @@ export function createActiveFrontend(options: ActiveFrontendOptions = {}): Activ
 
 		getTheme: () => theme,
 		setTheme: (nextTheme) => {
+			if (disposed) return;
 			theme = nextTheme;
 			notify();
 		},
 
 		getMode,
 		setMode: (mode) => {
+			if (disposed) return;
 			modeOverride = mode === 'auto' ? null : mode;
 			notify();
 		},
 
 		clearMode: () => {
+			if (disposed) return;
 			modeOverride = null;
 			notify();
 		},
@@ -203,11 +224,13 @@ export function createActiveFrontend(options: ActiveFrontendOptions = {}): Activ
 
 		getReducedMotion,
 		setReducedMotion: (reduced) => {
+			if (disposed) return;
 			reducedMotionOverride = reduced === 'auto' ? null : reduced;
 			notify();
 		},
 
 		clearReducedMotion: () => {
+			if (disposed) return;
 			reducedMotionOverride = null;
 			notify();
 		},
@@ -216,21 +239,28 @@ export function createActiveFrontend(options: ActiveFrontendOptions = {}): Activ
 
 		getReducedSound: () => reducedSound,
 		setReducedSound: (reduced) => {
+			if (disposed) return;
 			reducedSound = reduced;
 			notify();
 		},
 
 		getDensity: () => density,
 		setDensity: (nextDensity) => {
+			if (disposed) return;
 			density = nextDensity;
 			notify();
 		},
 
 		onPreferenceChange: (fn) => {
+			if (disposed) return () => {};
 			listeners.add(fn);
 			return () => listeners.delete(fn);
 		},
 
+		get disposed() {
+			return disposed;
+		},
+
 		dispose() {
 			if (disposed) return;
 			disposed = true;
diff --git a/src/arts/frontend/test/active-frontend.test.ts b/src/arts/frontend/test/active-frontend.test.ts
index d0414b9..e01d4e1 100644
--- a/src/arts/frontend/test/active-frontend.test.ts
+++ b/src/arts/frontend/test/active-frontend.test.ts
@@ -60,4 +60,35 @@ describe('createActiveFrontend()', () => {
 
 		frontend.dispose();
 	});
+
+	it('exposes disposed flag and silently ignores setters after dispose', () => {
+		const applied: StructuralChange[] = [];
+		const target = {} as HTMLElement;
+		const frontend = createActiveFrontend({
+			locale: 'es-ES',
+			theme: 'one',
+			target,
+			dom: { apply: (c) => applied.push(c) }
+		});
+
+		expect(frontend.disposed).toBe(false);
+		const beforeDispose = applied.length;
+		frontend.dispose();
+		expect(frontend.disposed).toBe(true);
+
+		// Re-dispose is idempotent.
+		expect(() => frontend.dispose()).not.toThrow();
+
+		// Setters after dispose are silent no-ops — neither apply DOM
+		// nor invoke listeners. Getters still read the last value.
+		frontend.setTheme('two');
+		frontend.setLocale('en-US');
+		frontend.setMode('dark');
+		expect(applied.length).toBe(beforeDispose);
+		expect(frontend.getTheme()).toBe('one');
+
+		// onPreferenceChange after dispose returns a no-op detacher.
+		const off = frontend.onPreferenceChange(() => {});
+		expect(() => off()).not.toThrow();
+	});
 });
diff --git a/src/arts/storage/engine-storage.ts b/src/arts/storage/engine-storage.ts
index bf4cd7c..701127a 100644
--- a/src/arts/storage/engine-storage.ts
+++ b/src/arts/storage/engine-storage.ts
@@ -10,6 +10,7 @@ import {
 import { createStorageDiagnostics, emitStorageDiagnostic } from './diagnostics';
 import { createEntryBus, type EntryBus } from './entry-bus';
 import { createStorageEntryRuntime } from './entry-runtime';
+import { StorageDisposedError } from './errors';
 import type {
 	EngineStorage,
 	EngineStorageOptions,
@@ -49,6 +50,8 @@ export function createEngineStorage(options: EngineStorageOptions = {}): EngineS
 		adapter: SyncStorageAdapter;
 	}>();
 
+	let disposed = false;
+
 	function report(ctx: Omit<StorageErrorContext, 'adapter'>, entryAdapterName: string): void {
 		const errorContext = { ...ctx, adapter: entryAdapterName };
 		emitStorageDiagnostic(diagnostics, STORAGE_DIAGNOSTIC_EVENTS.ERROR, errorContext);
@@ -64,6 +67,7 @@ export function createEngineStorage(options: EngineStorageOptions = {}): EngineS
 		defaults: T | (() => T),
 		entryOptions: StorageEntryOptions<T> = {}
 	): StorageEntry<T> {
+		if (disposed) throw new StorageDisposedError('entry');
 		const entryAdapter: SyncStorageAdapter = entryOptions.adapter ?? adapter;
 		const entryNamespace =
 			entryOptions.namespace === false ? undefined : (entryOptions.namespace ?? namespace);
@@ -142,6 +146,7 @@ export function createEngineStorage(options: EngineStorageOptions = {}): EngineS
 	}
 
 	function entriesSnapshot(): ReadonlyArray<{ key: string; fullKey: string; adapter: string }> {
+		if (disposed) throw new StorageDisposedError('entries');
 		return [...registeredEntries].map((r) => ({
 			key: r.key,
 			fullKey: r.fullKey,
@@ -150,6 +155,7 @@ export function createEngineStorage(options: EngineStorageOptions = {}): EngineS
 	}
 
 	function clear(): void {
+		if (disposed) throw new StorageDisposedError('clear');
 		// Snapshot first — `removeItem` does not mutate the registry, but
 		// future iterations of the design might, so this is defensive.
 		const snapshot = [...registeredEntries];
@@ -164,7 +170,6 @@ export function createEngineStorage(options: EngineStorageOptions = {}): EngineS
 		}
 	}
 
-	let disposed = false;
 	const handle: EngineStorage = {
 		adapter,
 		namespace,
diff --git a/src/arts/storage/errors.ts b/src/arts/storage/errors.ts
index 0f0535f..67d8d93 100644
--- a/src/arts/storage/errors.ts
+++ b/src/arts/storage/errors.ts
@@ -53,6 +53,14 @@ export const STORAGE_ERR_ENVELOPE_INVALID_VERSION: ErrCode = errCode(
 	'envelope_invalid_version'
 );
 
+/**
+ * `entry()`, `clear()`, `entries()` or any other public surface was
+ * invoked after `dispose()`. The engine's bus and adapter
+ * subscriptions are already torn down at that point — re-creating
+ * entries would silently leak.
+ */
+export const STORAGE_ERR_DISPOSED: ErrCode = errCode(STORAGE_ERR, 'disposed');
+
 /**
  * Human-readable messages for every error declared by `arts/stor`.
  * Indexed by `ErrCode` so the link to identity is direct. Each entry
@@ -72,7 +80,9 @@ export const STORAGE_ERROR_MESSAGES: ErrorMessages = {
 		`[${STORAGE_MODULE}] entry("${key}", ...) was called more than once with different defaults. The first registration wins; the second default is ignored.`,
 	[STORAGE_ERR_COOKIE_SERVER_REQUIRED]:
 		`[${STORAGE_MODULE}] cookieAdapter() runs in the browser only. For SSR use cookieAdapter.fromCookies(event.cookies, options).`,
-	[STORAGE_ERR_ENVELOPE_INVALID_VERSION]: `[${STORAGE_MODULE}] envelope.v not a number`
+	[STORAGE_ERR_ENVELOPE_INVALID_VERSION]: `[${STORAGE_MODULE}] envelope.v not a number`,
+	[STORAGE_ERR_DISPOSED]: (op: string): string =>
+		`[${STORAGE_MODULE}] ${op}() called on disposed storage`
 };
 
 /**
@@ -153,6 +163,15 @@ export class StorageEnvelopeInvalidVersionError extends CodeError {
 	}
 }
 
+export class StorageDisposedError extends CodeError {
+	readonly op: string;
+	constructor(op: string) {
+		const message = STORAGE_ERROR_MESSAGES[STORAGE_ERR_DISPOSED] as (op: string) => string;
+		super(STORAGE_ERR_DISPOSED, { message: message(op) });
+		this.op = op;
+	}
+}
+
 // ── Type guards ─────────────────────────────────────────────────────────
 
 export function isStorageInvalidTypeError(value: unknown): value is StorageInvalidTypeError {
@@ -194,3 +213,7 @@ export function isStorageEnvelopeInvalidVersionError(
 ): value is StorageEnvelopeInvalidVersionError {
 	return value instanceof StorageEnvelopeInvalidVersionError;
 }
+
+export function isStorageDisposedError(value: unknown): value is StorageDisposedError {
+	return value instanceof StorageDisposedError;
+}
diff --git a/src/arts/storage/index.ts b/src/arts/storage/index.ts
index b6678c6..b59509f 100644
--- a/src/arts/storage/index.ts
+++ b/src/arts/storage/index.ts
@@ -14,6 +14,7 @@ export {
 	STORAGE_ERR,
 	STORAGE_ERR_ASYNC_VALIDATE_UNSUPPORTED,
 	STORAGE_ERR_COOKIE_SERVER_REQUIRED,
+	STORAGE_ERR_DISPOSED,
 	STORAGE_ERR_ENTRY_DEFAULTS_MISMATCH,
 	STORAGE_ERR_ENVELOPE_INVALID_VERSION,
 	STORAGE_ERR_INVALID_TYPE,
@@ -22,6 +23,7 @@ export {
 	STORAGE_ERROR_MESSAGES,
 	StorageAsyncValidateUnsupportedError,
 	StorageCookieServerRequiredError,
+	StorageDisposedError,
 	StorageEntryDefaultsMismatchError,
 	StorageEnvelopeInvalidVersionError,
 	StorageInvalidTypeError,
@@ -29,6 +31,7 @@ export {
 	StorageValidationFailedError,
 	isStorageAsyncValidateUnsupportedError,
 	isStorageCookieServerRequiredError,
+	isStorageDisposedError,
 	isStorageEntryDefaultsMismatchError,
 	isStorageEnvelopeInvalidVersionError,
 	isStorageInvalidTypeError,
diff --git a/src/arts/storage/test/engine-storage.test.ts b/src/arts/storage/test/engine-storage.test.ts
index abd5c3e..0f6c6de 100644
--- a/src/arts/storage/test/engine-storage.test.ts
+++ b/src/arts/storage/test/engine-storage.test.ts
@@ -1,6 +1,7 @@
 import { describe, it, expect, vi } from 'vitest';
 import { createEngineStorage } from '../engine-storage';
 import { createMemoryAdapter } from '../adapters/memory';
+import { isStorageDisposedError, StorageDisposedError } from '../errors';
 import type { StorageErrorContext, SyncStorageAdapter } from '../types';
 
 function track(): {
@@ -548,4 +549,20 @@ describe('createEngineStorage — dispose', () => {
 		s.dispose();
 		expect(() => s.dispose()).not.toThrow();
 	});
+
+	it('throws StorageDisposedError on entry/clear/entries after dispose', () => {
+		const s = createEngineStorage({ adapter: createMemoryAdapter() });
+		s.dispose();
+
+		expect(() => s.entry('late', 'value')).toThrow(StorageDisposedError);
+		expect(() => s.clear()).toThrow(StorageDisposedError);
+		expect(() => s.entries()).toThrow(StorageDisposedError);
+
+		try {
+			s.entry('late', 'value');
+		} catch (err) {
+			expect(isStorageDisposedError(err)).toBe(true);
+			expect((err as StorageDisposedError).op).toBe('entry');
+		}
+	});
 });