Name the credential tool of a software-issued offer in the plan (issue 928)

internal/catalogue/handed.go

@@ -104,6 +104,9 @@ type PlanProvision struct {
 	Provider       string `json:"provider"`
 	ProviderModule string `json:"provider-module"`
 	CredentialForm string `json:"credential-form,omitempty"`
+	// CredentialTool is, for an offer whose credential the provider's software issues (issue 928), the provider's tool
+	// the vault asks for each holder's value; empty for any other form.
+	CredentialTool string `json:"credential-tool,omitempty"`
 	Path           string `json:"path,omitempty"`
 	// Contributes is what the consumer's manifest tells its provider for this provision (Manifest.Contributes: a
 	// database's name, its extensions), so the provider's helper learns it from the bus (issue 776). Nil where the
@@ -134,7 +137,7 @@ func provisionsOf(needs []Needed, module, as string, contributes map[string]map[
 			continue
 		}
 		p := PlanProvision{Provision: n.Name, Local: n.Local, Provider: n.From, ProviderModule: n.Module,
-			CredentialForm: n.CredentialForm, Contributes: maps.Clone(contributes[n.Name]),
+			CredentialForm: n.CredentialForm, CredentialTool: n.CredentialTool, Contributes: maps.Clone(contributes[n.Name]),
 			At: n.At, From: n.From, As: as}
 		// **A credential only a template names** (issue 788): named like a file's, so the client fills it from the
 		// vault's row for this holder.