Let villa's pyramid step start its worker pool inside the ZeroGPU worker

lasfield.py

@@ -437,6 +437,29 @@ def predict3d_argv(p, ct_input, out_json, checkpoint, device):
             "--device", device, "--no-download", "--flush-workers", "0", "--accumulator-workers", "0"]
 
 
+POOL_CPUS = 8                # pyramid processes predict3d may start (its default is every CPU of the host)
+
+
+@__import__("contextlib").contextmanager
+def _pool_friendly():
+    """Let predict3d's OME-Zarr pyramid step start its process pool when it runs inside a daemon process (ZeroGPU
+    runs a GPU call in one, and Python refuses children there), and cap that pool at POOL_CPUS. The pool's processes
+    only downsample chunks on the CPU. Restored on exit."""
+    import multiprocessing as mp
+    proc = mp.current_process()
+    was_daemon = proc._config.get("daemon")
+    real = mp.cpu_count
+    mp.cpu_count = lambda: max(1, min(POOL_CPUS, real()))
+    if was_daemon:
+        proc._config["daemon"] = False
+    try:
+        yield
+    finally:
+        mp.cpu_count = real
+        if was_daemon:
+            proc._config["daemon"] = was_daemon
+
+
 def run_villa_lasagna(p, ct_input, out_dir, device, checkpoint):
     """villa's predict3d in this process. Returns its exit code, wall seconds and the tail of its log."""
     import contextlib
@@ -456,7 +479,7 @@ def run_villa_lasagna(p, ct_input, out_dir, device, checkpoint):
             return len(s)
 
     try:
-        with contextlib.redirect_stdout(Tee()), contextlib.redirect_stderr(Tee()):
+        with contextlib.redirect_stdout(Tee()), contextlib.redirect_stderr(Tee()), _pool_friendly():
             rc = pco.cli_main(argv)
     except SystemExit as exc:
         rc = exc.code if isinstance(exc.code, int) else 1