Fetch API ↔ Chromium networking stack abort signal handling in Opera

Goal: verify whether Opera’s Fetch API retains the AbortSignal.reason value in the resulting error object when a request is terminated by a timeout‑initiated abort compared with an explicit controller.abort() call.

Constraints: the behavior may differ between Opera Desktop and Opera Android builds due to differing Chromium upstream versions, and network‑modifying extensions can alter abort‑signal propagation, making consistent observation difficult.

Questions: Does Opera preserve the abort reason for timeout‑triggered cancellations? Is the reason preserved identically for explicit aborts? Are there observable differences between Desktop and Android builds?