/**
 * IHeadRegistryDriver — pluggable per-key storage backend for head registries.
 *
 * Each (dbName, collectionName) pair maps to exactly one record. All operations
 * are O(1) — there is no global lock and no full-collection rewrite.
 *
 * Implementations:
 *  - InMemoryHeadRegistryDriver (brightchain-lib)  — Map-backed, browser-safe
 *  - FileHeadRegistryDriver (brightchain-db)        — one .json file per key
 *  - AzureBlobHeadRegistryDriver (brightchain-azure-store) — one blob per key
 *  - S3HeadRegistryDriver (brightchain-s3-store)    — one object per key
 */
/** The value stored for a single (dbName, collectionName) head pointer. */
export interface HeadRecord {
    blockId: string;
    /** ISO 8601 timestamp for last-writer-wins merge. */
    timestamp: string;
    /**
     * Block ID of the previous HeadRecord block written to the block store,
     * forming an immutable audit chain. Optional — set by callers that write
     * head record blocks. Enables conflict resolution via common-ancestor walk
     * (analogous to Git refs) and replicates for free with the block store.
     */
    prevHeadBlockId?: string;
}
export interface IHeadRegistryDriver {
    /**
     * Read the head record for the given composite key.
     * Returns null if no record exists.
     */
    readRecord(key: string): Promise<HeadRecord | null>;
    /**
     * Write (create or overwrite) the head record for the given key.
     */
    writeRecord(key: string, record: HeadRecord): Promise<void>;
    /**
     * Delete the head record for the given key.
     * Must not throw if the key does not exist.
     */
    deleteRecord(key: string): Promise<void>;
    /**
     * Return all stored keys.
     * Used by load() to hydrate the in-memory cache on startup.
     */
    listKeys(): Promise<string[]>;
}
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