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packages/foundation/data/web-workers/src/base-manager/helpers.md

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+# `helpers`
+
+## Purpose
+
+`helpers.ts` co-locates the small utilities the base manager and the
+message bus both depend on: a default wall-clock implementation, a default
+id generator backed by `crypto.getRandomValues`, the transfer-list validator
+that raises `WEB_WORKERS.INVALID_TRANSFER`, and a one-shot abort-signal
+wiring helper that returns a cleanup closure.
+
+Extracting them avoids duplication between `BaseWorkerManager` and
+`MessageBus` (both need clock, id-generator, and abort wiring) and keeps
+the base manager's main file under the 300-line ceiling.
+
+## Features
+
+- `defaultClock` — wall-clock `Date.now()` Clock implementation.
+- `defaultIdGenerator` — cryptographically random 16-hex-character ids.
+- `validateTransfer(transfer)` — passes through `undefined` and arrays,
+  throws `WebWorkersError(INVALID_TRANSFER)` for anything else (string,
+  object, number).
+- `wireAbortSignal(signal, onAbort)` — registers a one-shot abort listener
+  and returns a cleanup function that removes it.
+
+## Usage: Basic Example
+
+```ts
+import {
+    defaultIdGenerator,
+    validateTransfer,
+} from "@suaveplan/web-workers/base-manager";
+
+const id = defaultIdGenerator();
+const transfer = validateTransfer(opts?.transfer);
+```
+
+## Usage: Advanced Example
+
+```ts
+import { wireAbortSignal } from "@suaveplan/web-workers/base-manager";
+
+function withAbort<T>(
+    signal: AbortSignal | undefined,
+    onTimeout: () => void,
+    promise: Promise<T>
+): Promise<T> {
+    const cleanup = wireAbortSignal(signal, onTimeout);
+    return promise.finally(() => {
+        cleanup?.();
+    });
+}
+```
+
+## API Reference
+
+- `defaultClock: Clock` — `() => Date.now()`.
+- `defaultIdGenerator: IdGenerator` — `() => string` returning 16
+  lowercase-hex chars (64 bits of entropy).
+- `validateTransfer(transfer: Transferable[] | undefined): Transferable[] | undefined`
+  — pass-through on undefined / array; throws on non-array.
+- `wireAbortSignal(signal: AbortSignal | undefined, onAbort: () => void): (() => void) | undefined`
+  — returns a cleanup closure or `undefined` when `signal` is undefined.
+
+## Implementation Notes
+
+`defaultIdGenerator` uses `crypto.getRandomValues(new Uint8Array(8))` and
+hex-encodes the bytes. 64 bits of entropy is sufficient for per-process
+RPC correlation (`birthday-paradox` collision probability is < 1e-9 for
+fewer than 10⁵ outstanding requests). `wireAbortSignal` uses
+`addEventListener('abort', listener, { once: true })` so the listener
+removes itself after firing — the returned cleanup is therefore safe to
+call any number of times. `validateTransfer` is intentionally permissive
+on the array's contents (it doesn't try to prove every element is actually
+`Transferable`); structured-clone will throw at `postMessage` time if a
+non-transferable slips in. Surfacing that error is the transport's job,
+not the validator's.