fix(flac): add FLAC frame-sync scan to getAlignedSegmentSize; extend IFormatDecoder rawData param

StreamDecoder peeks candidate bytes; FlacFormatDecoder scans backward for 0xFF/0xF8 sync. Fixes mid-stream decode failure where segments started mid-frame.

DeepDrftPublic/Interop/audio/StreamDecoder.ts

@@ -244,20 +244,31 @@ export class StreamDecoder {
 
         const segmentSize = 64 * 1024; // 64KB segments
         const availableBytes = this.totalRawBytes - this.processedBytes;
+
+        // Peek the candidate window first so the aligner can scan for a format-specific
+        // frame boundary (FLAC). extractAlignedData is non-destructive — it reads from
+        // rawChunks without advancing processedBytes — so reading before alignment is safe.
+        const peekSize = Math.min(segmentSize, availableBytes);
+        if (peekSize === 0) return null;
+        const peekBytes = this.extractAlignedData(peekSize);
+
         // Passing streamComplete lets the aligner relax the min-frame guard
         // for the final tail; otherwise residual <512-byte tails get dropped.
         const alignedSize = this.formatDecoder!.getAlignedSegmentSize(
             this.formatInfo,
             availableBytes,
             segmentSize,
-            this.streamComplete
+            this.streamComplete,
+            peekBytes
         );
 
         if (alignedSize <= 0) return null;
 
         const segmentOffset = this.processedBytes;
 
-        const rawSegment = this.extractAlignedData(alignedSize);
+        // alignedSize is always ≤ peekSize ≤ peekBytes.length, so subarray is in-bounds
+        // and zero-copy — no second extraction needed.
+        const rawSegment = peekBytes.subarray(0, alignedSize);
         const decodableSegment = this.formatDecoder!.wrapSegment(this.formatInfo, rawSegment);
 
         try {