Keep the builds of the grants step's machine alone, not of every machine its composition resolves (repo-check of #230)

Composing the bus's machine resolves the others on the same context, and
a machine never recorded as sent refused the whole composition.

cmd/mesh-controller/recorded_kept.go

@@ -63,19 +63,24 @@ func keptExcept(ctx context.Context) (map[string]bool, bool) {
 
 type keepEveryBuildKey struct{}
 
-// keepingEveryBuild is a context whose sends compose every module — recorded or rolling out — at the build
-// its machine was last sent (novox/hq issue 490): the grants step, which sends the machine holding the bus
-// its new user list and nothing of any module's new code. That code waits there for a gate like any other
-// move; the list must not, or the first machine's gate is judged against a bus that refuses what the change
-// newly grants.
-func keepingEveryBuild(ctx context.Context) context.Context {
-	return context.WithValue(ctx, keepEveryBuildKey{}, true)
+// keepingEveryBuild is a context whose sends compose every module of one machine — recorded or rolling out —
+// at the build that machine was last sent (novox/hq issue 490): the grants step, which sends the machine
+// holding the bus its new user list and nothing of any module's new code. That code waits there for a gate
+// like any other move; the list must not, or the first machine's gate is judged against a bus that refuses
+// what the change newly grants.
+//
+// **That machine alone.** Composing one machine resolves the others too — who is on the private network,
+// who answers a requirement — on the same context, and those are no part of the step's send: they are
+// composed as any send composes them. Kept for every machine, a machine whose last send is not known
+// refused the bus's machine's composition.
+func keepingEveryBuild(ctx context.Context, node string) context.Context {
+	return context.WithValue(ctx, keepEveryBuildKey{}, node)
 }
 
-// everyBuildKept is whether this context keeps every module at the build its machine runs.
-func everyBuildKept(ctx context.Context) bool {
-	on, _ := ctx.Value(keepEveryBuildKey{}).(bool)
-	return on
+// everyBuildKept is whether this context keeps every module of this machine at the build it runs.
+func everyBuildKept(ctx context.Context, node string) bool {
+	on, _ := ctx.Value(keepEveryBuildKey{}).(string)
+	return on != "" && on == node
 }
 
 // recordedKept is, for a send under keepingRecorded, every recorded module the machine was last sent a
@@ -87,7 +92,7 @@ func everyBuildKept(ctx context.Context) bool {
 // 490), and a machine whose last send is not known refuses the send: there is nothing to keep it at, and
 // composing the mesh's builds would be the very move the grants step must not make.
 func recordedKept(ctx context.Context, open *stores, node string) (map[string]string, error) {
-	every := everyBuildKept(ctx)
+	every := everyBuildKept(ctx, node)
 	skip, on := keptExcept(ctx)
 	if !on && !every {
 		return nil, nil
@@ -150,7 +155,7 @@ func keepRecorded(ctx context.Context, open *stores, node string, shelf map[stri
 		if err != nil {
 			return nil, err
 		}
-		if !found && everyBuildKept(ctx) {
+		if !found && everyBuildKept(ctx, node) {
 			return nil, fmt.Errorf("%s runs %s's build %s, which the build records no longer hold: the bus's user "+
 				"list cannot be sent there alone with it kept (novox/hq issue 490)", node, m, short(kept[m]))
 		}