--version printed "dev" for any binary not built with make build, so a
user running a go install build could not say what version they had.
resolveVersion now falls back to the module version from
runtime/debug.ReadBuildInfo() when the build-time stamp is absent,
ignoring the "(devel)" of a local build. The stamped value still wins
when present. It takes the build info as an argument, so a test covers
the choice without a real build.
Model: opus-4-8
