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packages/devtools/tooling/sandbox/src/worker-engine/worker-engine.md

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+# WorkerEngine
+
+<!-- begin:auto-docs -->
+_(no submodules)_
+<!-- end:auto-docs -->
+
+## Purpose
+
+`WorkerEngine` uses real `node:worker_threads` for true OS-thread isolation. Each `execute` call spawns a fresh `Worker` constructed from an inline source string (`eval: true`), posts the code + context + modules over the structured-clone message channel, and awaits the structured reply. Intrinsics are NOT shared with the host realm — the worker has its own V8 isolate, its own heap, and its own event loop. Timeouts are enforced by calling `worker.terminate()`, which is a hard stop the running script cannot intercept.
+
+Use `WorkerEngine` when the code being sandboxed may be adversarial: a true OS-thread boundary defeats the prototype-chain escapes that compromise `vm-engine`. The cost is per-call worker startup, which is non-trivial; pair with `SandboxPool` when latency matters.
+
+## Features
+
+- Real `node:worker_threads` execution — OS-thread isolation.
+- Worker spawned per call, terminated after every result.
+- `worker.terminate()` enforces timeout — script cannot intercept.
+- Structured-clone passes context + modules.
+- Output-size cap applied inside the worker before postMessage.
+- OTel `recordExecution` + `recordDuration` per call.
+
+## Usage: Basic
+
+```ts
+import { WorkerEngine } from "@suaveplan/sandbox/worker-engine";
+
+const e = new WorkerEngine({
+    timeout: 5000,
+    maxOutputSize: 1024,
+    memoryLimit: 50 * 1024 * 1024,
+});
+const r = await e.execute("2 + 2");
+e.destroy();
+```
+
+## Usage: Advanced
+
+Wrap the engine in a pool to amortise startup:
+
+```ts
+import { SandboxPool } from "@suaveplan/sandbox/pool";
+import { WorkerEngine } from "@suaveplan/sandbox/worker-engine";
+
+const pool = new SandboxPool({
+    minSize: 2,
+    maxSize: 8,
+    engineConfig: { timeout: 5000, maxOutputSize: 1024, memoryLimit: 5e7 },
+    factory: (cfg) => new WorkerEngine(cfg),
+});
+```
+
+## API Reference
+
+- `new WorkerEngine(config: SandboxEngineConfig)`.
+- `execute(code, context?, options?): Promise<SandboxResult>`.
+- `registerModule(mod): void`.
+- `unregisterModule(name): boolean`.
+- `reset(): void`.
+- `destroy(): void`.
+
+## Implementation Notes
+
+The inline worker source is a single string literal. The worker uses a
+runtime `Reflect.construct(Function, [...keys, source])` to wrap the user
+code in an isolated function scope — this is acceptable inside the worker
+because the worker IS the security boundary. Outside the worker, in the host,
+no dynamic code construction happens. The post-message channel uses
+structured clone, which copies primitives + plain objects + typed arrays but
+not functions or symbols — module exports must therefore be data, not host
+references; for host bridges use `spawn-engine` plus an IPC channel.