/**
 * One-shot boot migration of the pre-schema preference keys (`___viewer_mode`
 * / `___preview_mode` / `___ui-scale`) to their schema-typed `efp-*`
 * equivalents — the keys the debug panel edits and `UIState` prefers. Runs
 * before anything reads the keys (`load()` calls it ahead of `loadConfig`).
 *
 * Copy, not move: the legacy keys stay in place for a release or two so a
 * rollback to an older SDK still sees them (their readers keep a fallback);
 * only an explicit disable/reset seed removes both generations. An existing
 * `efp-*` value always wins — a stale legacy key must not clobber it.
 *
 * `storage` is injectable for tests; the default is the real `localStorage`
 * when it is usable.
 */
export declare function migrateLegacyStorageKeys(storage?: Pick<Storage, 'getItem' | 'setItem'> | undefined): void;
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