V42+V42A: fix seam click khi loop master FX — worklet wrap crossfade (tail->head) + native WebAudio loop cho bypass (het click beat 0); dip bypass 5ms; PDC playhead freeze/snap

app/api/v1/plugins.py

@@ -1123,6 +1123,16 @@ async def ws_fx_realtime(websocket: WebSocket, session_id: str):
         # tới worklet kịp khi main-thread stall chặn cả 2 hướng (fade nằm trong
         # browser queue, tới sau khi worklet đã cạn buffer → click vẫn còn), và
         # fade-in sau stall tạo dip âm lượng định kỳ = vibrato/wow&flutter.
+        # V34 diag: pump gap log - bridge khong san xuat block (SHM rong) > 30ms
+        # => fxrt_pump.log (phan biet bridge stall vs Python pump stall).
+        _plog = os.environ.get("FXRT_PUMP_LOG")
+        if not _plog:
+            _ad = os.environ.get("APPDATA")
+            _plog = os.path.join(_ad, "SonicForgeDAW", "logs", "fxrt_pump.log") if _ad else ""
+        _pf = open(_plog, "a", buffering=1) if _plog else None
+        _pump_last = None
+        if _pf is not None:
+            _pf.write("%d pump_start\n" % int(_time.time() * 1000))
         _last_lat = None
         try:
             while True:
@@ -1147,6 +1157,13 @@ async def ws_fx_realtime(websocket: WebSocket, session_id: str):
                     # time.sleep dùng high-res waitable timer -> poll đúng 2ms.
                     await asyncio.to_thread(_time.sleep, 0.002)
                     continue
+                if _pf is not None:
+                    _now = _time.time()
+                    if _pump_last is not None:
+                        _gap = (_now - _pump_last) * 1000.0
+                        if _gap > 30.0:
+                            _pf.write("%d pump_gap %.0f n=%d\n" % (int(_now * 1000), _gap, len(blks)))
+                    _pump_last = _now
                 for _blk in blks:
                     await websocket.send_bytes(_blk)
         except Exception: