Key provisions by one rule the plan, the seat and the assigner share (issue 774)

The assigner's rule 8 waited for a key for every `requires`, while the plans named only the needs of handed modules:
every new build of grafana, dnsmasq, mesh-knowledge, mesh-mail and the builders waited for a key nobody would make,
and grafana, not handed, had no plan, so no route key and no route on route-proxy.

catalogue.Keyed is the rule (a need a module answers is keyed when its consumer is handed or the provider's helper
answers it), catalogue.Awaited the same rule from manifests for the assigner, and a module not handed now has a plan
for what a helper answers of it. Handed modules' plans are unchanged.

Quick fix: drop the missing-key check from rule 8. Thorough fix (chosen): one rule in mesh-sdk all three parts use,
since the kind (three parts deciding the same set apart) already drifted once and hid failures as waits.

go/compose/resolve.go

@@ -54,6 +54,7 @@ func (c *composer) planFor(nodeName string) (Resolved, error) {
 		// Issued for this holder alone and kept by the vault (issue 757).
 		resolved.Needs[i].IssuedToHolder = issuedToHolder(shelf, n)
 		resolved.Needs[i].ProviderMoved = providerMoved(shelf, n)
+		resolved.Needs[i].AnsweredByHelper = answeredByHelper(shelf, n)
 		if n.ByRecord {
 			// Answered by something the mesh holds, so there is no pair-wise secret between two machines.
 			licence, _ := c.licence(n.From)
@@ -189,6 +190,16 @@ func providerMoved(shelf map[string]catalogue.Manifest, n catalogue.Needed) bool
 	return known && (movedProvider(provider) || provider.AnsweredByHelperFor(n.Name))
 }
 
+// answeredByHelper is whether a need's provider offers it answered by the provider helper (issue 792): keyed by the seat
+// mesh-provisioner for every consumer, handed or not (catalogue.Keyed, issue 774).
+func answeredByHelper(shelf map[string]catalogue.Manifest, n catalogue.Needed) bool {
+	if n.ByRecord || n.Module == "" {
+		return false
+	}
+	provider, known := shelf[n.Module]
+	return known && provider.AnsweredByHelperFor(n.Name)
+}
+
 // movedProvider is whether a provider's credentials are the vault's: the module is marked moved, or it holds the
 // mesh-vault seat (issue 793).
 func movedProvider(m catalogue.Manifest) bool {