One runtime principal per node carries every assigned module's tools (hq ADR 0175, to-be 38 WP2.1)

Where the node-tools module is assigned, the machine's bus user list gains one principal of kind
node-tools in place of that module's own: it may subscribe every carried module's tool namespace
and every held seat's verbs on its node, read and follow every membership on its node, call any
tool anywhere, answer what it is asked — and consume nothing, because tools are what it runs.
Every other module keeps its own principal, so a module still serving tools from its container
holds its own credential until it moves.

Named exactly as the module it stands for, so `module issue` and `rollout mint` deliver its
credential through the path a module's already takes, into node-tools' own `broker` secret. The
runtime module's name is one constant in each of the broker and catalogue packages, held to one
string by the agreement test, because a rule turns on it.

internal/broker/users.go

@@ -62,13 +62,33 @@ func Users(r Records) ([]Principal, error) {
 
 	for _, node := range sortedCopy(r.Nodes) {
 		out = append(out, Principal{Kind: KindNode, Node: node})
+		// **Where the runtime is assigned, the machine gets one runtime principal in place of the
+		// runtime module's own** (novox/hq ADR 0175, to-be 38). It carries every module on the
+		// node: its serving grants are the union of theirs. Every other module keeps its own
+		// principal — a module still serving tools from its own container holds its own
+		// credential until it moves, and the two serve side by side in the meantime.
+		runtimeHere := false
 		for _, d := range r.Assigned[node] {
+			if d.Module == RuntimeModule {
+				runtimeHere = true
+			}
+		}
+		for _, d := range r.Assigned[node] {
+			if runtimeHere && d.Module == RuntimeModule {
+				continue
+			}
 			out = append(out, Principal{
 				Kind: KindModule, Node: node, Module: d.Module,
 				Emits: d.Emits, Consumes: d.Consumes, Serves: d.Serves,
 				Holds: d.Holds, Uses: d.Uses, Watches: d.Watches, Invokes: d.Invokes,
 			})
 		}
+		if runtimeHere {
+			out = append(out, Principal{
+				Kind: KindNodeTools, Node: node, Module: RuntimeModule,
+				Carries: append([]Declared(nil), r.Assigned[node]...),
+			})
+		}
 	}
 	for _, node := range sortedCopy(r.Enrolling) {
 		out = append(out, Principal{Kind: KindEnrolment, Node: node})