fix: "Download as .py" in WASM run-mode exports

[moble]

📝 Summary

(I got a lot of help writing the test from Claude.)

When a notebook is exported with marimo export html-wasm --mode run, the resulting HTML embeds the notebook source in a <marimo-code> element, but the "Download as .py" menu item fails with "Failed to read code / Not implemented".

The reason is that PyodideBridge.readCode() calls this.saveRpc.readNotebook(). In read mode, getSaveWorker() returns a stub where every method is throwNotImplemented, which is what causes that failure.

This PR fixes the problem by checking in readCode if the app mode is "read", and if so it just reads the file from domElementFileStore.

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Project	Deployment	Actions	Updated (UTC)
marimo-docs	Ready	Preview, Comment	Apr 20, 2026 1:09pm

[Copilot]

Pull request overview

Fixes “Download as .py” for marimo export html-wasm --mode run by making the WASM bridge read notebook source from the embedded <marimo-code> element when running in read-mode, avoiding the read-mode SaveWorker stub that throws “Not implemented”.

Changes:

• Import and use domElementFileStore in PyodideBridge.readCode() when getInitialAppMode() === "read".
• Keep existing SaveWorker-based readNotebook() path for non-read modes.

[Copilot]

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[vercel]

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[Copilot]

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[Light2Dark]

Thanks @moble.
Not sure why we disabled it before, deferring to @dmadisetti or @mscolnick .

On the implementation, is it possible to implement this in the readNotebook path? Instead of throwNotImplemented?

[moble]

On the implementation, is it possible to implement this in the readNotebook path? Instead of throwNotImplemented?

Yeah, I wasn't sure that it wouldn't mess up something else. But I've switched to that now. Thanks.