This is really interesting, in many ways it's similar to the system used for building golangnews - generators, asset pipeline, custom handlers, handlers returning an error, partials and layouts for templates, migrations, query builder. The type Context interface is pretty bloated though - this is the disadvantage of trying to stick everything into one param for handlers - it becomes a god object which knows and does too much.
Interesting to see a few solutions from different people converging, probably partly because of previous experience with other frameworks like Rails. To those who say you don't need a framework, I think it depends on the style of application you're building; if a service you'd probably be quite happy with just the stdlib, but if you're building a full web app which serves html, the stdlib is lacking in some areas. Trying to avoid using a framework will just mean reinventing your own solutions for authentication/authorisation, layouts, forms, persistence, assets etc - basically building your own ad-hoc framework instead. That's not always a bad thing but there are certain elements that almost every web app (as opposed to service) requires.