Web-only extensions with customEditors contribution silently fail to register (e.g. pomdtr.excalidraw-editor)

[medampudi]

Summary

Web-only VS Code extensions (extensions that declare browser but not main in package.json) that contribute a customEditor silently fail to register in code-server. The custom editor never appears in "Open With…" and files open in the default text editor. No error is surfaced to the user.

Repro

Environment:

• code-server 1.115.0 (commit 1c6fb2dc200eb57c5c7d612004e18a5e6ae8b0ed, x64)
• Host: Ubuntu 24.04 LTS, accessed via browser over Tailscale
• Fresh user install directory (no prior config)

Steps:

1. code-server --install-extension pomdtr.excalidraw-editor (v3.9.0)
2. sudo systemctl restart code-server
3. Hard-reload the browser tab
4. Open any *.excalidraw file

Expected: file opens in the Excalidraw canvas editor (as it does in VS Code Desktop and vscode.dev).

Actual: file opens in the plain-text JSON editor. "Open With…" does not list "Excalidraw Editor". No error in the extension host log. The extension is installed and listed via code-server --list-extensions.

Affected extensions (all web-only customEditor contributors)

Extension	Version	browser	main
pomdtr.excalidraw-editor	3.9.0	./dist/extension.js	(none)
lrstanley.excalidraw-editor	3.7.4	./dist/extension.js	(none)
telesoho.excalidraw-editor-cj	3.4.6	./dist/extension.js	(none)

Same pattern observed with other web-only customEditor extensions.

Expected behavior

Either:

1. Web-only extensions with customEditor contributions load correctly (they work in VS Code Desktop's webview and in vscode.dev), OR
2. code-server surfaces a clear error at install time or file-open time explaining that web-only custom editors are not supported in this environment, so users can choose an alternative.

Current silent failure is the worst of both worlds.

Verification that extension is installed

$ code-server --list-extensions --show-versions
pomdtr.excalidraw-editor@3.9.0

Extension directory structure is intact:

~/.local/share/code-server/extensions/pomdtr.excalidraw-editor-3.9.0-universal/
├── assets/
├── dist/extension.js
├── package.json
└── webview/

Happy to provide logs or test a patch if someone picks this up.

[code-asher]

I see vscode.dev and desktop work, but does this trigger in Codespaces or with native VS Code web (the serverful version, code serve-web)? I would imagine this needs to be resolved upstream in VS Code rather than maintaining a patch for it here.

[code-asher]

I tried on Codespaces but podmdtr.excalidraw-editor fails to even activate when I install it via command line.

If I install it via the U, or use the "install in browser" button, then it works (after reloading the page).

I think VS Code has an issue when web extensions are installed via the cli, they do not actually get loaded as web extensions until some explicit action from the UI?

But then I tried in code-server and the .excalidraw files actually load for me just fine after installing the extension via the command line (4.115.0 on Firefox). So I am not sure what is going on.