A held module is composed exactly as before it joined, at the build its machine runs, so its port, resources and
contributions stay. A joining module's directories belong to its user and its own group, and its tools' directories
are refused closed to that group; the runner joins it where the engine can say so. A take records the root and is
taken only when the engine states the act done. Libraries' paths and verdicts count modules pulled in by a
requirement, and a unit takes the identity.
jschoubben