Intermittent ModuleNotFoundError when upgrading a pure‑Python package via <py-env> in PyScript

Symptom

When the <py-env> tag is updated to request a newer version of a pure‑Python wheel, subsequent <py-script> blocks sometimes fail with ModuleNotFoundError or continue to use the old cached version.

Goal

Determine a reliable pattern that lets a small browser‑based application load a new package version without a full page reload while guaranteeing that the code that follows sees the updated module.

Constraints and uncertainty

• micropip.fetch (or the implicit load from <py-env>) runs asynchronously; the wheel extraction may not finish before the next script block executes.
• Already imported modules are not automatically reloaded, so stale references persist unless the page is reloaded or importlib.reload is used.
• There is no built‑in version‑gated loading mechanism; developers must manage aliases or manual reloads.

These factors make it unclear which approach—awaiting micropip.fetch, using an onload handler, or wrapping imports in a reload function—provides deterministic zero‑downtime migration for a pure‑Python dependency.

What is the recommended way to ensure the new package is fully extracted and available before dependent <py-script> blocks run? Can the onload attribute of <py-env> be relied upon to swap imports safely without a page reload? Is it necessary to re‑import the module via importlib.reload after the load completes, or are there alternative patterns that avoid manual reloading?