# manager-helpers

## Purpose

Small free helpers extracted from `manager.ts` to keep the class file
under CLAUDE.md §3's 300-line hard cap. Both helpers (`deriveCacheKey`
and `checkAbortedSignal`) are exercised through the manager's tests;
they have no state and can be reused by any future internal collaborator
that needs the same primitives.

## Features

- `deriveCacheKey(url, verifyKey?)` — stable cache key derivation that
  appends the first 8 bytes (hex) of the verify-key as a suffix so
  two loads against the same URL with different verify-keys live in
  separate cache slots.
- `checkAbortedSignal(signal, resolver, key?)` — throw
  `PackerBrowserError(ABORTED)` when the supplied signal is already
  aborted; tolerates `undefined` for both `signal` and `resolver` so
  it works at every call site.

## Usage: Basic Example

```ts
import { checkAbortedSignal, deriveCacheKey } from "./manager-helpers.js";

const key = deriveCacheKey("/asset.packed");
const keyed = deriveCacheKey("/asset.packed", new Uint8Array(64));
checkAbortedSignal(new AbortController().signal, undefined);
```

## Usage: Advanced Example

```ts
import { checkAbortedSignal, deriveCacheKey } from "./manager-helpers.js";
import { defaultPackerBrowserResolver } from "../i18n/messages.js";

const ac = new AbortController();
ac.abort();
try {
    checkAbortedSignal(
        ac.signal,
        defaultPackerBrowserResolver,
        "packer-browser.error.ABORTED.preload"
    );
} catch (err) {
    console.error("preload aborted", err);
}
```

## API Reference

- `deriveCacheKey(url: string, verifyKey?: Uint8Array): string`.
- `checkAbortedSignal(signal: AbortSignal | undefined, resolver?: MessageResolver, key?: string): void`.

## Implementation Notes

- The 8-byte cap on the verify-key prefix balances key uniqueness
  against cache-key memory cost. A full key would be 32 bytes hex-
  encoded (64 chars) per entry; the 8-byte prefix is enough to
  discriminate adversarially-distinct keys.
- `checkAbortedSignal` accepts a custom message key so the same helper
  works for `manager.load`, `manager.preload`, `manager.loadStream`,
  and future async surfaces.
- These helpers are NOT part of the public barrel — they're internal
  implementation details of the manager. Direct imports from outside
  the manager module are discouraged.