Try to compose metaschema inline with togglable param.

test-suite/metaschema-xspec/json-schema-gen/json-schema-gen.xspec

@@ -6,9 +6,11 @@
    stylesheet="../../../toolchains/xslt-M4/schema-gen/make-json-schema-metamap.xsl"
    run-as="external" xmlns:ov="http://csrc.nist.gov/ns/oscal/test/variable">
 
+   <!--<x:param name="compose-metaschema-first">true()</x:param>-->
+
    <x:scenario label="When generating a JSON schema from composed Metaschema definitions">
       <x:scenario label="if it has a defined field with no constraint and no allowed-values">
-         <x:context href="json-value-testing-mini-metaschema-COMPOSED.xml"
+         <x:context href="json-value-testing-mini-metaschema.xml"
             select="/*/m:define-field[@name='unconstrained']"/>
          <x:expect label="the resulting JSON Schema should not have an enum to enforce it." xmlns="http://www.w3.org/2005/xpath-functions">
             <map key="oscal-value-testing-mini-oscal-value-testing-mini:unconstrained">
@@ -35,7 +37,7 @@
       </x:scenario>
 
       <x:scenario label="if it has a defined field with a constraint, allowed-values, strict enforcement of allow-other='no' and explicit target of '.'">
-         <x:context href="json-value-testing-mini-metaschema-COMPOSED.xml"
+         <x:context href="json-value-testing-mini-metaschema.xml"
             select="/*/m:define-field[@name='constrained-closed']"/>
          <x:expect label="the resulting JSON Schema should have an enum to enforce it." xmlns="http://www.w3.org/2005/xpath-functions">
             <map key="oscal-value-testing-mini-oscal-value-testing-mini:constrained-closed">
@@ -74,7 +76,7 @@
       </x:scenario>
 
       <x:scenario label="if it has a defined field with a constraint, allowed-values, no explicit target, and permissive enforcement of allow-other='yes'">
-         <x:context href="json-value-testing-mini-metaschema-COMPOSED.xml"
+         <x:context href="json-value-testing-mini-metaschema.xml"
             select="/*/m:define-field[@name='constrained-open']"/>
          <x:expect label="the resulting JSON Schema should not have an enum to enforce it." xmlns="http://www.w3.org/2005/xpath-functions">
             <map key="oscal-value-testing-mini-oscal-value-testing-mini:constrained-open">
@@ -113,7 +115,7 @@
       </x:scenario>
 
       <x:scenario label="if it has a defined field with a constraint, allowed-values, strict enforcement of allow-other='no' and explicit target other than '.'">
-         <x:context href="json-value-testing-mini-metaschema-COMPOSED.xml"
+         <x:context href="json-value-testing-mini-metaschema.xml"
             select="/*/m:define-field[@name='constrained-narrow']"/>
          <x:expect label="the resulting JSON Schema should not have an enum to enforce it." xmlns="http://www.w3.org/2005/xpath-functions">
             <map key="oscal-value-testing-mini-oscal-value-testing-mini:constrained-narrow">
@@ -140,7 +142,7 @@
       </x:scenario>
 
       <x:scenario label="if it has a defined field with a constraint, allowed-values, permissive enforcement of allow-other='yes' and explicit target other than '.'">
-         <x:context href="json-value-testing-mini-metaschema-COMPOSED.xml"
+         <x:context href="json-value-testing-mini-metaschema.xml"
             select="/*/m:define-field[@name='constrained-sortof']"/>
          <x:expect label="the resulting JSON Schema should not have an enum to enforce it." xmlns="http://www.w3.org/2005/xpath-functions">
             <map key="oscal-value-testing-mini-oscal-value-testing-mini:constrained-sortof">

toolchains/xslt-M4/schema-gen/make-json-schema-metamap.xsl

@@ -2,6 +2,7 @@
 <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
     xmlns:xs="http://www.w3.org/2001/XMLSchema"
     xmlns:math="http://www.w3.org/2005/xpath-functions/math" exclude-result-prefixes="xs math"
+    xmlns:nm="http://csrc.nist.gov/ns/metaschema"
     version="3.0" xmlns="http://www.w3.org/2005/xpath-functions"
     xpath-default-namespace="http://csrc.nist.gov/ns/oscal/metaschema/1.0" expand-text="true">
 
@@ -15,9 +16,23 @@
     <xsl:strip-space elements="METASCHEMA define-assembly define-field model"/>
 
     <xsl:output indent="yes" method="xml"/>
-
+
+    <!-- This parameter controls whether this transform will compose the source metaschema as part of running this
+         stylesheet in standalone mode for debugging. In the CI and CD pipelines for production, this is unusual and
+         not desired, so this parameter is not enabled by default and set to false(). For unit testing and local debug
+         scenarios, you will want this so you do not save intermediate "composed" metaschemas needed for JSON Schema
+         generation, so with Oxygen, Saxon on the CLI, or Saxon via API you would set this to `true()`. -->
+    <xsl:param name="compose-metaschema-first" select="true()"/>
+
     <xsl:template match="/" priority="2">
-        <xsl:apply-templates/>
+        <xsl:choose>
+            <xsl:when test="$compose-metaschema-first = true()">
+                <xsl:sequence select="nm:compose-metaschema(/)"/>
+            </xsl:when>
+            <xsl:otherwise>
+                <xsl:apply-templates/>
+            </xsl:otherwise>
+        </xsl:choose>
     </xsl:template>
 
     <xsl:variable name="home" select="/"/>
@@ -31,6 +46,7 @@
     <xsl:key name="flag-definition-by-name"     match="METASCHEMA/define-flag"     use="@_key-name"/>
 
     <xsl:import href="../nist-metaschema-COMPOSE.xsl"/>
+
     <xsl:variable name="composed-metaschema" select="/"/> 
 
     <xsl:template match="/METASCHEMA" expand-text="true">