Stop hearing mesh.assignment: a process follows its membership from the grants part's state alone

ADR 0571 clause 10: the grants part publishes memberships on mesh.assignment until the lease write and stops
then. FollowMembership now reads and watches its own key of the state memberships and nothing else, and refuses
to follow, naming the state, when it cannot read it (there is nothing else to follow, and a silent follow of
nothing is the fault). A module's principal and the runtime lose their subscribe on mesh.assignment; the grants
part's publish grant stays until the write (S21 stops the publishing).

Tests: TestFollowMembershipHearsWhatIsIssuedToTheAccount (integration) edited: no state is a refusal, a
membership put in the state is applied, one published on the subject is not; run locally against its
embedded bus. Rows added to TestTheCopiedComposerComposesAsTheControllers: nobody subscribes mesh.assignment,
and the controller's golden grant of it is the one row the copy now lacks. No new test function.

(issue 774, 774/S5)

Claude-Session: https://claude.ai/code/session_01NcbgfJ9Gum47zkFKWRaovL

go/buscompose/buscompose_test.go

@@ -161,8 +161,11 @@ func grantsAsTheControllers(t *testing.T, got, want string) {
 		intended := beyondTheControllers(user)
 		for g := range was {
 			// A runtime's direct get of its membership from the assignments stream went with the stream (research 072
-			// row 33): it reads the grants part's state memberships instead (ADR 0571 clause 7).
-			if !now[g] && !strings.HasPrefix(g, "$JS.API.DIRECT.GET."+AssignmentsStream+".mesh.assignment."+strings.SplitN(user, ".", 2)[0]+".") {
+			// row 33): it reads the grants part's state memberships instead (ADR 0571 clause 7). And it no longer hears
+			// the subject, where the grants part stops publishing at the lease write (ADR 0571 clause 10, issue 774).
+			node := strings.SplitN(user, ".", 2)[0]
+			if !now[g] && !strings.HasPrefix(g, "$JS.API.DIRECT.GET."+AssignmentsStream+".mesh.assignment."+node+".") &&
+				!strings.HasPrefix(g, "mesh.assignment."+node+".") {
 				t.Errorf("%s: the copy does not grant %s, which the controller's does", user, g)
 			}
 		}
@@ -880,6 +883,17 @@ func healthChecks(t *testing.T) {
 		if u.Kind == KindModule && MayPublish(perms, "$KV.mesh-delivery-assigner_policies.x") {
 			t.Errorf("%s writes the assigner's policies", u.Username())
 		}
+		// ADR 0571 clause 10 (issue 774, 774/S5/AC2): nobody hears memberships on mesh.assignment; they are read from
+		// the grants part's state.
+		if MaySubscribe(perms, "mesh.assignment.a.restic") {
+			t.Errorf("%s hears mesh.assignment", u.Username())
+		}
+	}
+	// Nor the runtime carrying the node's modules, which reads each one's membership from the state.
+	if perms, err := PermissionsFor(Principal{Kind: KindNodeTools, Node: "a", Module: RuntimeModule,
+		Carries: []Declared{{Module: "restic"}}}); err != nil || MaySubscribe(perms, "mesh.assignment.a.restic") ||
+		!MayPublish(perms, "$JS.API.DIRECT.GET.KV_mesh-grants_memberships.$KV.mesh-grants_memberships.a.restic") {
+		t.Errorf("the runtime hears mesh.assignment or reads no membership: %v", err)
 	}
 	// 1953 S-age (ADR 0565 §10): a log that says an age keeps its entries that long and no longer; one that says none, as
 	// long as the log (ADR 0297).