Hold a joining module at the build it ran, own its directories by its own group, and take a library only when its act is done (hq ADR 0328 review, ADR 0334)

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.

internal/catalogue/declaration.go

@@ -261,9 +261,10 @@ type Rendering struct {
 	LibraryGroups  map[string]int
 	TakenLibraries map[string]bool
 	LibraryPaths   map[string][]string
-	// Held is, by module, the library a joining module that ran here before waits on: until every library it uses
-	// is taken its containers keep the user they ran as, so it is left out of the declaration (§8).
-	Held map[string]string
+	// RunnerJoinsOwnGroups says this machine's engine puts the tool runner's account in a joining module's own group
+	// (novox/hq ADR 0334 §2: its statement's contract is link.OwnGroupContract or later); to an older one the
+	// identity's runner is not sent.
+	RunnerJoinsOwnGroups bool
 }
 
 // RootField is a user resource's field saying the account must never become root without a person