/**
 * Eager Blob Downloader
 *
 * Downloads unresolved blobs in the background when blobMode='eager'.
 * Called after sync completes to prefetch blobs for offline access.
 *
 * Strategy:
 *   1. Snapshot the primary keys of all rows currently flagged
 *      `_hasBlobRefs=1` for each syncable table.
 *   2. Walk that key list in chunks via `bulkGet`. Each `bulkGet`
 *      triggers the blob-resolve middleware, which does all the actual
 *      work — downloading blobs (throttled and deduplicated by the
 *      shared BlobDownloadTracker) and enqueueing them for persistence
 *      via the internal save queue.
 *
 * This keeps a single, symmetric code path with normal application
 * reads, which is important when other middlewares are present
 * (e.g., a hypothetical encryption middleware): writes from the save
 * queue and reads from this loop both pass through the full middleware
 * stack, so on-disk representation stays consistent.
 *
 * Why a snapshot of primary keys (rather than re-querying the index)?
 *   - Rows that get resolved by parallel application reads simply
 *     disappear from the table contents we're about to re-fetch; the
 *     middleware skips them since `_hasBlobRefs` is already cleared.
 *   - Stuck rows (e.g., blob 404s) are naturally bypassed: we just
 *     advance to the next chunk in the snapshot. No `seenKeys`
 *     bookkeeping required.
 *   - The snapshot is `string[]`-shaped for typical Dexie Cloud rows
 *     (~36 bytes/UUID), so ~28K keys per MB. Acceptable for any
 *     realistic dataset.
 *
 * Progress is tracked automatically via liveQuery in blobProgress.ts —
 * no manual progress reporting needed here.
 *
 * --- Throughput note ---
 * The chunk loop is sequential: bulkGet → wait for all downloads to
 * settle → next bulkGet. The save queue drains in the background and
 * does not block iteration (saves no longer need to be persisted before
 * the next iteration, since we don't re-query the index). For typical
 * blob sizes (10 KB – 10 MB) the network dominates total time. If
 * real-world profiling later shows the per-chunk fixed cost matters,
 * the next bulkGet could be kicked off in parallel with the current
 * one's middleware work — but we keep it simple until measurements
 * justify otherwise.
 */
import { BehaviorSubject } from 'rxjs';
import { DexieCloudDB } from '../db/DexieCloudDB';
/**
 * Download all unresolved blobs in the background.
 *
 * This is called when blobMode='eager' (default) after sync completes.
 */
export declare function downloadUnresolvedBlobs(db: DexieCloudDB, downloading$: BehaviorSubject<boolean>, signal?: AbortSignal): Promise<void>;