`go get -u` takes the highest semver the proxy offers: a fork's stray tag
sorting above its real branch, or a module that has moved and kept
tagging under the old path. Resolving first refuses both, and names the
compare link for every version that does move.
Keeps the interlocked pins current and reports what it could not move.
Areas apply, gate and commit one at a time, so a dependency that breaks
the build costs one commit rather than the whole pull request.