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docs/foundation/flow/streams-chunk-queue/src/storage-adapter/persister.md

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+# storage-adapter / persister
+
+<!-- begin:auto-docs -->
+_(no submodules)_
+<!-- end:auto-docs -->
+
+## Purpose
+
+Bridges `@suaveplan/storage` `AbstractStorage` onto the queue's
+`ChunkPersister` contract. Persistence enables resuming an interrupted
+transfer: every received chunk is written through to a key-value
+backend (IndexedDB in browsers, file-backed stores on the server)
+keyed by `file:<fileId>:chunk:<chunkId>` so a fresh queue with the
+same `fileId` can hydrate via `loadAllChunks`.
+
+## Features
+
+- Deterministic key layout (`chunkStorageKey`, `chunkStoragePrefix`).
+- Persists chunk bytes alongside the metadata via the storage backend's
+  optional `metadata` slot.
+- Loads a single chunk or lists every persisted chunk id for the
+  configured `fileId`, in ascending order.
+- Structural `ChunkStorageLike` view so tests can substitute a Map.
+
+## Usage: Basic
+
+```ts
+import { MemoryStorage } from "@suaveplan/storage";
+import { StorageChunkPersister } from "@suaveplan/streams-chunk-queue";
+
+const storage = new MemoryStorage();
+const persister = new StorageChunkPersister({ storage, fileId: 12345n });
+```
+
+## Usage: Advanced
+
+```ts
+import { IndexedDBStorage } from "@suaveplan/storage";
+
+const storage = await IndexedDBStorage.open("downloads", "chunks");
+const persister = new StorageChunkPersister({
+    storage,
+    fileId: 12345n,
+});
+const queue = new StreamingChunkQueue({
+    fileId: 12345n,
+    totalChunks: 100n,
+    persister,
+});
+await queue.loadAllChunks();
+```
+
+## API Reference
+
+### `chunkStorageKey(fileId, chunkId)` → `string`
+
+`file:<fileId>:chunk:<chunkId>`.
+
+### `chunkStoragePrefix(fileId)` → `string`
+
+`file:<fileId>:chunk:`.
+
+### `ChunkPersister`
+
+```ts
+interface ChunkPersister {
+    persist(chunk: StoredChunk): Promise<void>;
+    load(chunkId: bigint): Promise<Uint8Array | undefined>;
+    listChunkIds(): Promise<bigint[]>;
+}
+```
+
+### `StorageChunkPersister`
+
+```ts
+new StorageChunkPersister({ storage, fileId });
+```
+
+Implements `ChunkPersister` over any `ChunkStorageLike`. `listChunkIds`
+filters by prefix, parses the trailing segment as `bigint`, and sorts
+ascending — the ordering means
+`StreamingChunkQueue.loadAllChunks` ingests in the canonical chunk
+order.
+
+## Implementation Notes
+
+`BigInt` is converted to `string` before being stored in storage
+metadata so the JSON wire form is portable. The persister does NOT
+attempt to delete entries — chunks are durable until the consumer
+explicitly clears the underlying storage. Keys with an empty trailing
+segment (`file:7:chunk:`) are silently dropped from `listChunkIds`
+because they cannot be parsed as a bigint.