Go 1.27 looks the zero version of a workspace member up once a build loads the module graph; a versioned replace is the form it takes with no lookup. workspaceOf writes the use list and those replaces, and a unit case loads such a graph with GOPROXY=off. The only go.work the build path writes is this fixture's: the build module itself places requirements by replaces in its modfile (pins.go), which are unversioned and not in a workspace, so they are untouched. Claude-Session: https://claude.ai/code/session_01NcbgfFSnn24M3GcqttoU7i