Take the suffix of internal names from the Input and never the environment: Input.InternalSuffix and a local internal-name helper, so the package doc is true (review round 1, finding 5). The test failed first; the suite is 1257 tests in 1.04 s

go/compose/input.go

@@ -12,6 +12,7 @@
 // same refusals in the same words, so that a comparison node for node is a fair one.
 //
 // It imports the standard library and mesh-sdk's own packages only.
+// It reads no environment variable: the range the mesh allocates from and the suffix of its internal names are fields of Input.
 package compose
 
 import (
@@ -42,6 +43,9 @@ type Input struct {
 	// OverlayCIDR is the range the mesh allocates from when no tunnel was adopted, as genesis was told it (the
 	// controller's OverlayCIDRVar); empty means DefaultOverlayCIDR. The package reads no environment.
 	OverlayCIDR string
+	// InternalSuffix is what the mesh's internal names end in (the controller's MESH_INTERNAL_SUFFIX), with or without a leading
+	// dot; empty means overlay.DefaultSuffix. A fact of the whole mesh, so it is in the Input and never read from the environment.
+	InternalSuffix string
 	// Tunnels is, by node name, the found tunnel whose key is the node's overlay key (inv.Tunnels).
 	Tunnels map[string]FoundTunnel
 	// Adopted is the hub's found tunnel and the hub's name, whether or not the hub took it (inv.AdoptedTunnel); nil