compose: an offer of form none composes no credential and holds nothing

After the controller, nothing makes a pair row for a new consumer, so a need whose provider offers no credential
(form none) was composed with a stand-in on both ends and the node-engine held the consumer (issue 1126:
mesh-cli on ace, "stands in for the grant of mcp-endpoint"). The vault never mints for form none, so such a need
now composes with no credential: the consumer's need carries none, the provider's grant carries the consumer
and nothing sealed, neither is named foreseen, CredentialsNeeded asks the vault for neither, and no empty grant
file is written.

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

go/compose/credentials_needed.go

@@ -19,7 +19,8 @@ type CredentialKey struct {
 // as a consumer, each need of its resolution a provider's credential answers (a need answered by a record is a licence's,
 // not a pair's); as a provider, each credential it must carry a grant for (rowsFor). A node that composes its own asks the
 // vault for exactly these, sealed to its key, and composes with them; one it does not get is stood in for, which the
-// node's own apply refuses (CompositionsApplied).
+// node's own apply refuses (CompositionsApplied). A need whose provider offers it with no credential (form none) is
+// in neither list: the vault mints nothing for it (issue 1126).
 func CredentialsNeeded(in Input, node string) (asConsumer, asProvider []CredentialKey, err error) {
 	c := newComposer(in)
 	resolved, err := c.resolution(node)
@@ -27,7 +28,7 @@ func CredentialsNeeded(in Input, node string) (asConsumer, asProvider []Credenti
 		return nil, nil, err
 	}
 	for _, n := range resolved.Needs {
-		if n.ByRecord || n.From == "" {
+		if n.ByRecord || n.From == "" || credentialless(n) {
 			continue
 		}
 		asConsumer = append(asConsumer, CredentialKey{Provision: n.Name, Consumer: node, ConsumerModule: n.For,
@@ -38,6 +39,10 @@ func CredentialsNeeded(in Input, node string) (asConsumer, asProvider []Credenti
 		return nil, nil, fmt.Errorf("compose: the credentials %s provides: %w", node, err)
 	}
 	for _, r := range rows {
+		// A grant whose offer presents no credential (form none) has none to ask for (issue 1126).
+		if consumer, err := c.planFor(r.Consumer); err == nil && credentiallessRow(consumer.Plan, r, node) {
+			continue
+		}
 		asProvider = append(asProvider, CredentialKey{Provision: r.Provision, Consumer: r.Consumer,
 			ConsumerModule: r.ConsumerModule, Provider: node, Local: r.Local})
 	}