Update Ableton export to use dedicated arrangement time signature ID generation

src/lib/exporters/ableton/builders.ts

@@ -1102,22 +1102,40 @@ function getTimeSignatureId(timeSignature: { numerator: number; denominator: num
   );
 }
 
+function getArrangementTimeSignatureId(timeSignature: {
+  numerator: number;
+  denominator: number;
+}) {
+  const signature = `${timeSignature.numerator}/${timeSignature.denominator}`;
+  const timeSignatureId = TIME_SIGNATURES[signature];
+  if (timeSignatureId === undefined) {
+    throw new Error(
+      `Arrangement export has no verified Ableton Live time-signature ID for ${signature}`,
+    );
+  }
+  return timeSignatureId;
+}
+
 function buildArrangementTimeSignatureEvents(
   sections: AblArrangementSection[],
   fallbackTimeSignature: { numerator: number; denominator: number },
 ) {
   const initialTimeSignature = sections[0]?.timeSignature || fallbackTimeSignature;
+  const initialTimeSignatureId =
+    sections.length > 0
+      ? getArrangementTimeSignatureId(initialTimeSignature)
+      : getTimeSignatureId(initialTimeSignature);
   const events = [
     {
       '@Id': 0,
       '@Time': -63072000,
-      '@Value': getTimeSignatureId(initialTimeSignature),
+      '@Value': initialTimeSignatureId,
     },
   ];
-  let previousTimeSignatureId = getTimeSignatureId(initialTimeSignature);
+  let previousTimeSignatureId = initialTimeSignatureId;
 
   sections.forEach((section, index) => {
-    const timeSignatureId = getTimeSignatureId(section.timeSignature);
+    const timeSignatureId = getArrangementTimeSignatureId(section.timeSignature);
     if (index === 0 || timeSignatureId === previousTimeSignatureId) {
       previousTimeSignatureId = timeSignatureId;
       return;
@@ -1162,7 +1180,9 @@ export async function buildProject(projectData: ProjectRawData, exporterParams:
     transformedData.arrangementSections[0]?.timeSignature ||
     projectData.scenesSettings.timeSignature;
   (project.Ableton.LiveSet.MasterTrack.DeviceChain.Mixer as any).TimeSignature.Manual['@Value'] =
-    getTimeSignatureId(initialTimeSignature);
+    transformedData.arrangementSections.length > 0
+      ? getArrangementTimeSignatureId(initialTimeSignature)
+      : getTimeSignatureId(initialTimeSignature);
   project.Ableton.LiveSet.MasterTrack.AutomationEnvelopes.Envelopes.AutomationEnvelope[0].Automation.Events.EnumEvent =
     buildArrangementTimeSignatureEvents(
       transformedData.arrangementSections,