/**
 * Namespaced key/value store for app and middleware metadata.
 *
 * `(namespace, key)` is the composite identity. Keep both values separate;
 * joining them with a delimiter can create collisions.
 */
export interface MetadataStore {
    /** Return the value for `(namespace, key)`, or `null` when it is absent. */
    get: (namespace: string, key: string) => Promise<unknown | null>;
    /** Insert or replace the value for `(namespace, key)`. */
    set: (namespace: string, key: string, value: unknown) => Promise<void>;
    /** Delete `(namespace, key)`. Do nothing when it is absent. */
    delete: (namespace: string, key: string) => Promise<void>;
    /**
     * Optional. The value with a revision, or `null` when it is absent. Pair it
     * with `setIf` for compare-and-set writes: implement both or neither.
     * Every write (also a plain `set`) gives the key a new revision, and a
     * revision does not come back after a `delete`.
     */
    getVersioned?: (namespace: string, key: string) => Promise<{
        value: unknown;
        revision: string;
    } | null>;
    /**
     * Optional. Write only when the current revision is `expectedRevision`
     * (`null` means the key is absent). Success is `{ ok: true, revision }`.
     * A different revision returns `{ ok: false, reason: 'conflict' }`.
     */
    setIf?: (namespace: string, key: string, value: unknown, expectedRevision: string | null) => Promise<{
        ok: true;
        revision: string;
    } | {
        ok: false;
        reason: 'conflict';
    }>;
}
export declare const MetadataCapability: import('./capabilities.js').Capability<MetadataStore, "metadata">;
export declare const getMetadata: import('./capabilities.js').CapabilityGetter<MetadataStore>, provideMetadata: import('./capabilities.js').CapabilityProvider<MetadataStore>;