Useless interfaces and interface distillation https://ane.github.io/2017/03/23/useless-interfaces.html (only factor out an interface when you have multiple classes!)
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An interesting feature of the Grok TiddlyWiki interface: it has the sidebar on the right.
I see a sidebar on the left way more often, but arguably it makes more sense on the right for a wiki? The content is effectively more prominent.
https://groktiddlywiki.com/read/
It is remarkably hard to escape command line arguments safely on Windows, and the standard libraries of multiple languages have needed patching: https://flatt.tech/research/posts/batbadbut-you-cant-securely-execute-commands-on-windows/
It feels like a mature software project is one where bugs require multiple commits to fix.
You've hammered out the basic issues, so the remaining issues are often weird interactions between components.