Keep the mesh's trust anchors at the terminal, refuse containerd's tree, and read a found directory as a wait

The review of #170: step-ca's root, roots and path and the identity
provider's issuer are what every consumer trusts, and any caller of the
settings verb could replace them; they are now terminal keys like places and
accesses (hq issue 339). /var/lib/containerd joins the runtimes' data. And a
directory the node-engine uses as found failed its module's gate and rolled
its builds back; found before the send, it is now a wait for a person the
gate passes with, as a relogin is (ADR 0254), and only one the send itself
found holds the module.

internal/link/protocol.go

@@ -446,6 +446,14 @@ const KindUnit = "unit"
 // starting ReasonRelogin when only a new login is missing.
 const KindAccount = "account"
 
+// KindDirectory is a directory of a module that the node-engine uses as found (novox/hq issue 339): there before
+// the mesh, with another owner or mode than declared, and left so until a person hands it over at the machine
+// (`mesh-host hand-over`). Stated unhealthy with a reason that starts ReasonUsedAsFound.
+const KindDirectory = "directory"
+
+// ReasonUsedAsFound starts the reason of a directory used as found.
+const ReasonUsedAsFound = "used as found:"
+
 // ReasonRelogin starts the reason of an account whose running session began before it was put in a group
 // (ADR 0252): the build did what it should, and a person has one step left (novox/hq ADR 0254).
 const ReasonRelogin = "relogin needed"