/**
 * Content-addressed store for attachment bytes.
 *
 * Attachment content is immutable for a given (UIDVALIDITY, UID, part) — IMAP
 * guarantees it — so it is addressed by the SHA-256 of its bytes rather than
 * by message coordinates. Three properties fall out of that:
 *
 * - **Dedup is free.** The same PDF forwarded across threads and accounts is
 *   stored once.
 * - **Reads are verified.** Every read re-hashes; corrupted or tampered
 *   content is removed and reported as a miss rather than handed to a caller.
 *   This is why writes need no fsync discipline — a torn file cannot match
 *   its own name, so it is unreachable garbage the next read cleans up.
 * - **Writes are atomic.** Content lands in a temp file in its final
 *   directory, created 0600, then renamed into place.
 *
 * Paths shard on the first two hex characters of the digest, the layout git
 * and npm's cacache both use, to keep directory entry counts bounded.
 *
 * The index that maps messages to digests lives in SQLite (`attachment`
 * table); this class knows nothing about mail. Everything here is safe to
 * delete at any time, per the XDG cache contract.
 */
export interface StoredBlob {
    sha256: string;
    size: number;
}
export default class BlobStore {
    private readonly root;
    constructor(root: string);
    private static digest;
    /** `<root>/ab/abcdef…` — sharded to bound directory size. */
    private pathFor;
    /**
     * Store content, returning its address. Writing content that is already
     * held is a no-op beyond the hash.
     */
    put(content: Buffer): Promise<StoredBlob>;
    /**
     * Read content back, verifying it against its address.
     *
     * @returns the bytes, or undefined when absent or corrupt.
     */
    get(sha256: string): Promise<Buffer | undefined>;
    /** Remove content. Absent content is not an error. */
    delete(sha256: string): Promise<void>;
    /** Every digest currently held, for orphan reconciliation against the index. */
    list(): string[];
    /** Total bytes held, counted toward the shared cache budget. */
    sizeBytes(): number;
}
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