# ADR 0001: Run Piper in an ES module worker

## Decision

Bundle the Piper worker as an ES module and start it with `new Worker(url, { type: 'module' })`.

## Context

Piper loads ONNX Runtime Web and its WebAssembly loader dynamically. The current IIFE/classic worker bundle reports `TypeError: "undefined" cannot be parsed as a URL` during WASM backend initialization, even though the pinned same-origin ONNX loader and binary are available. This is consistent with module-relative URL metadata being lost in the classic bundle.

## Consequences

The browser must support module workers. Current supported browser targets already require modern WebAssembly and worker support. CI asserts that the worker is built and started in module mode; production acceptance remains the real deployed browser flow.