Your product's Edit button opens a real desktop app

Your SaaS stores users' images. They keep asking for "basic editing": which, scoped honestly, means rebuilding a fraction of GIMP in JavaScript over six months.

So don't. Each user's container runs GIMP with their files. Your "Advanced edit" button opens an iframe whose src is that container's display URL with ?decorations=false&toolbar=false: no window chrome, no menus, just the application filling the modal. The user crops, masks, exports. The file lands back in their container's storage, where your app already reads it.

Per-user containers sound expensive until the substrate does its work: every clone shares the same GIMP binary blocks on disk, the kernel caches them once, and idle sessions cost nearly nothing.