Local dev: No "main" config key or "index.js" file found for plugin

[samwinslow]

Bug description

When locally developing a plugin, after adding it via Advanced > Install Local Plugin, sometimes the plugin errors out with No "main" config key or "index.js" file found for plugin, even though plugin.json is valid and index.js exists.

Sometimes restarting the plugin server seems to fix this, sometimes not.

A current workaround is just to code in the source editor rather than load local plugins, but it's a sharp UX papercut.

Expected behavior

Reads config file and index.js correctly

How to reproduce

1. Create or clone a known working plugin
2. Install via file path