Ask over mesh-sdk's composition: a question makes no pair credential and reads the mesh once (issue 1387)

The callers that only ask (status, the doctor's probes, facts, bindings, data, acts, nodes show, images, release, recorded push, consumers) resolve through resolveNode and compose through composeQuestion, over one Input read per operation (withInputCache). A question composes with Reading or Foreseeing and never calls PairCredential's maker: the credential a send would make is named, and perform makes it on a send.

cmd/mesh-controller/acts.go

@@ -314,7 +314,7 @@ type afterAct struct {
 // after the write, which can only find more unmet than the closure would: a seat said held there is
 // held in the closure too.
 func resolvedAfter(ctx context.Context, open *stores, shelf map[string]catalogue.Manifest, node string) afterAct {
-	plan, _, err := planFor(ctx, open, node)
+	plan, _, err := resolveNode(ctx, open, node)
 	if err == nil {
 		out := afterAct{plan: plan, unheld: plan.Unheld}
 		for _, m := range plan.Modules {
@@ -355,6 +355,8 @@ func splitModules(field string) []string {
 // Nothing here can fail the act it reports on. A mesh that cannot be read is worth saying and is
 // not a reason to claim the assignment did not happen — it did.
 func blockedElsewhere(ctx context.Context, open *stores, except string) string {
+	// One reading of the mesh for every machine this looks at.
+	ctx = withInputCache(ctx)
 	nodes, err := open.inventory.Nodes(ctx)
 	if err != nil {
 		return "\n\nThe rest of the mesh could not be checked: " + err.Error()
@@ -364,7 +366,7 @@ func blockedElsewhere(ctx context.Context, open *stores, except string) string {
 		if n.Name == except {
 			continue
 		}
-		if _, _, err := planFor(ctx, open, n.Name); err != nil {
+		if _, _, err := resolveNode(ctx, open, n.Name); err != nil {
 			blocked[n.Name] = err.Error()
 		}
 	}