/**
 * StorageBackend abstraction — pluggable blob storage.
 * FsBackend ships natively; S3 support via @backloghq/termlog-s3 (separate package).
 */
/**
 * Streaming write handle returned by `StorageBackend.createWriteStream`.
 * Chunks become visible at the target path only after `end()` resolves.
 * `abort()` discards the in-progress write and leaves nothing at the path.
 */
export interface BlobWriteStream {
    write(chunk: Buffer): Promise<void>;
    /** Atomically commits all written chunks to `path`. */
    end(): Promise<void>;
    /** Discards the in-progress write. */
    abort(): Promise<void>;
}
/** Thrown when a StorageBackend cannot open or complete a streaming write. */
export declare class WriteStreamError extends Error {
    constructor(message: string);
}
export interface StorageBackend {
    readBlob(path: string): Promise<Buffer>;
    writeBlob(path: string, data: Buffer): Promise<void>;
    listBlobs(prefix: string): Promise<string[]>;
    deleteBlob(path: string): Promise<void>;
    /**
     * Open a streaming write handle for `path`. Chunks written via `write()` are
     * buffered/streamed but not visible until `end()` commits atomically.
     * On error call `abort()` to clean up.
     */
    createWriteStream(path: string): Promise<BlobWriteStream>;
    /**
     * Append `data` to the end of `path`, creating it if absent.
     * Optional — callers fall back to read-modify-writeBlob on backends that omit this.
     * Implementations must fsync before returning so data survives a crash.
     */
    appendBlob?(path: string, data: Buffer): Promise<void>;
    /** Hint for concurrency caps — true when backed by the local filesystem. */
    isLocalFs?(): boolean;
}
/**
 * Local filesystem backend. Atomic writes use a `.tmp` sidecar + rename.
 * All paths are relative to the root directory supplied at construction.
 */
export declare class FsBackend implements StorageBackend {
    private readonly root;
    constructor(root: string);
    isLocalFs(): boolean;
    private abs;
    readBlob(path: string): Promise<Buffer>;
    /** Atomic write: write to a unique <path>.<nonce>.tmp, fsync it, rename over <path>, fsync the directory. */
    writeBlob(path: string, data: Buffer): Promise<void>;
    /**
     * List all blob paths (relative to root) whose basename starts with `prefix`.
     * Searches only the root directory (no recursive walk — all termlog files live flat).
     */
    listBlobs(prefix: string): Promise<string[]>;
    deleteBlob(path: string): Promise<void>;
    /**
     * Append `data` to `path` using O_APPEND (atomic at the kernel level for
     * writes <= PIPE_BUF on the same filesystem), then fsync for crash durability.
     */
    appendBlob(path: string, data: Buffer): Promise<void>;
    createWriteStream(path: string): Promise<BlobWriteStream>;
}
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