Give every module an identity and ask once to keep a shared folder (hq ADR 0325, issue 575)

A module's containers that declare identity run as an identity the controller allocates once, mesh-wide,
from 50000-59999; each access names its users and whether its folder is taken; an access wait is excused
for a folder the mesh may not keep yet, and the operator is asked once per folder and machine, the folder
taken only on the warrant. All of it is sent only to an engine at contract 5. A placement for an access a
newer build brings is judged against that build (issue 575). mesh-host pinned to the ADR 0325 branch head.

testdata/beside/mesh-host/internal/apply/placement_guard.go.captured

@@ -523,6 +523,20 @@ func refusedPlaces(resources []declaration.Resource) map[string]error {
 		switch res := r.(type) {
 		case *declaration.Directory:
 			err = refusePath(res.Path, placingDirectory, moduleOfID(res.ID), res.Owner)
+			// And outside every home, the walk's judgement before anything is applied (novox/hq issue 358): a
+			// link another account could make in its path refuses it, and with it what is below it, whatever
+			// order they are declared in. The apply walks again at the moment of use. A directory handed over
+			// keeps its own, stricter walk (issue 356), which refuses any link at all.
+			if err == nil && meshDirsByDescriptor && homeAbove(res.Path) == "" &&
+				!HandedOver()[handOverKey(res.ID, res.Path)] {
+				if judged := judgeMeshDir(res.Path); judged != nil {
+					err = judged
+					var link *LinkInPathError
+					if errors.As(judged, &link) {
+						err = &PlacementRefusedError{Path: res.Path, Why: "it " + link.why()}
+					}
+				}
+			}
 		case *declaration.Access:
 			err = refusePath(res.Path, placingAccess, moduleOfID(res.ID), "")
 		default: