resolver generates invalid/incompatible trees on update

[zkat]

When dependencies are updated in package.json to a version incompatible with previously-installed dependents, the dependents don't re-evaluate their dependencies, and the tree ends up in an invalid state.

The repro is pretty easy:

1. npx create-react-app react-app && cd react-app && rm -rf node_modules package-lock.json
2. cargo run -- add lodash@3

Using cargo run here in debug mode is important, because it's the debug_assertions for validating trees that caught this.