fix: pre-roll metronome ticks are missing

src/core/audio-interface/KGAudioInterface.ts

@@ -42,6 +42,10 @@ export class KGAudioInterface {
   private isPlaying: boolean = false;
   private masterVolume: number = AUDIO_INTERFACE_CONSTANTS.DEFAULT_MASTER_VOLUME;
   private scheduledEvents: Set<number> = new Set(); // Tone event IDs
+  private delayedTransportStartTimeoutId: number | null = null;
+  private delayedTransportStartMs: number = 0;
+  private virtualPrerollStartBeat: number | null = null;
+  private virtualPrerollStartTimeMs: number | null = null;
 
   // Master volume control
   private masterGain: Tone.Gain | null = null;
@@ -390,6 +394,7 @@ export class KGAudioInterface {
   public preparePlayback(project: KGProject, startPosition: number): void {
     // Clear any existing scheduled events
     this.clearScheduledEvents();
+    this.clearDelayedTransportStart();
 
     console.log("Preparing playback");
 
@@ -440,8 +445,18 @@ export class KGAudioInterface {
         console.log("Loop mode disabled");
       }
 
+      if (startPosition < 0) {
+        this.delayedTransportStartMs = Math.abs(startPosition) * secondsPerBeat * 1000;
+        this.virtualPrerollStartBeat = startPosition;
+        this.virtualPrerollStartTimeMs = null;
+      } else {
+        this.delayedTransportStartMs = 0;
+        this.virtualPrerollStartBeat = null;
+        this.virtualPrerollStartTimeMs = null;
+      }
+
       // Set transport position (convert beats to Tone.js format)
-      this.setTransportPosition(startPosition);
+      this.setTransportPosition(Math.max(0, startPosition));
 
       // Start metronome if enabled
       if (this.isMetronomeEnabled) {
@@ -646,8 +661,19 @@ export class KGAudioInterface {
       if (!this.isAudioContextStarted) {
         throw new Error('Audio context not started');
       }
-      
-      Tone.Transport.start();
+
+      if (this.delayedTransportStartMs > 0 && this.virtualPrerollStartBeat !== null) {
+        this.virtualPrerollStartTimeMs = performance.now();
+        this.delayedTransportStartTimeoutId = window.setTimeout(() => {
+          this.delayedTransportStartTimeoutId = null;
+          this.virtualPrerollStartBeat = null;
+          this.virtualPrerollStartTimeMs = null;
+          Tone.Transport.start();
+        }, this.delayedTransportStartMs);
+      } else {
+        Tone.Transport.start();
+      }
+
       this.isPlaying = true;
       
       console.log('Audio playback started');
@@ -662,6 +688,7 @@ export class KGAudioInterface {
    */
   public stopPlayback(): void {
     try {
+      this.clearDelayedTransportStart();
       Tone.Transport.stop();
       this.metronome.stop();
 
@@ -789,7 +816,8 @@ export class KGAudioInterface {
   public setTransportPosition(position: number): void {
     try {
       // Convert beats to Tone.js time format
-      const toneTime = this.beatsToToneTime(position);
+      const safePosition = Math.max(0, position);
+      const toneTime = this.beatsToToneTime(safePosition);
       Tone.Transport.position = toneTime;
       console.log(`Set transport position to ${position} beats (${toneTime})`);
     } catch (error) {
@@ -802,6 +830,14 @@ export class KGAudioInterface {
    */
   public getTransportPosition(): number {
     try {
+      if (this.virtualPrerollStartBeat !== null && this.virtualPrerollStartTimeMs !== null) {
+        const project = KGCore.instance().getCurrentProject();
+        const secondsPerBeat = 60 / project.getBpm();
+        const elapsedSeconds = (performance.now() - this.virtualPrerollStartTimeMs) / 1000;
+        const elapsedBeats = elapsedSeconds / secondsPerBeat;
+        return Math.min(0, this.virtualPrerollStartBeat + elapsedBeats);
+      }
+
       const position = Tone.Transport.position;
       return this.toneTimeToBeats(position);
     } catch (error) {
@@ -973,6 +1009,17 @@ export class KGAudioInterface {
     return this.captureStream;
   }
 
+  private clearDelayedTransportStart(): void {
+    if (this.delayedTransportStartTimeoutId !== null) {
+      window.clearTimeout(this.delayedTransportStartTimeoutId);
+      this.delayedTransportStartTimeoutId = null;
+    }
+
+    this.delayedTransportStartMs = 0;
+    this.virtualPrerollStartBeat = null;
+    this.virtualPrerollStartTimeMs = null;
+  }
+
   // ===== PRIVATE UTILITY METHODS =====
 
   /**