/**
* Shared `localStorage` persistence for components that expose a `storage-key` attribute.
*
* Every access is guarded twice: once around the `localStorage` call itself (the whole API throws,
* not just returns null, in Safari private browsing, in a sandboxed iframe without
* `allow-same-origin`, and when a site-data policy blocks storage), and once around
* `JSON.parse`/`JSON.stringify`. Persistence is a convenience, never a correctness requirement, so
* both functions fail silently rather than surfacing an error into a Lit lifecycle callback --
* throwing out of `willUpdate()`/`updated()` would break rendering over a storage quota.
*/
/**
* Reads a JSON value previously written by `writePersistedState()` for `key`, or `null` if the key
* is unset, storage is unavailable, the key is missing, the stored text is malformed, or the parsed
* value fails `isValid`.
*
* `isValid` is a type guard, so callers get a typed result with no separate cast, and a stored value
* whose shape has drifted (an older release's format, or another script writing the same key) is
* rejected instead of being trusted.
*/
export declare function readPersistedState<T>(key:string|undefined,isValid:(parsed:unknown)=>parsed is T):T|null;
/**
* Writes `value` as JSON under `key`. A no-op for an unset key -- persistence is opt-in, so a
* component with no `storage-key` must not touch storage at all. Any failure (quota exceeded,
* private browsing, sandboxed iframe, a value that cannot be serialized) is silently ignored.
*/
export declare function writePersistedState(key:string|undefined,value:unknown):void;