Fix Neutron backend API compatibility and multiprocessing fallback

backends/nxp/backend/neutron_converter_manager.py

@@ -78,23 +78,35 @@ def convert(self, tflite_model: bytes, target: str) -> bytes:
         cctx.compilationOpts.minNumOpsPerGraph = 1
         cctx.compilationOpts.excludeGraphPasses = "MergeTranspose"
 
-        logger = multiprocessing.log_to_stderr()
-        logger.setLevel(logging.WARNING)
-        queue = multiprocessing.Manager().Queue()
+        # Try to use multiprocessing for isolation, but fall back to direct execution
+        # if the environment doesn't support it (e.g., in sandcastle/build environments)
+        try:
+            logger = multiprocessing.log_to_stderr()
+            logger.setLevel(logging.WARNING)
+            queue = multiprocessing.Manager().Queue()
+
+            process = multiprocessing.Process(
+                target=convert_unsafe,
+                args=(self.neutron_converter, tflite_model, cctx, queue),
+            )
+            process.start()
+            process.join()  # waits until the subprocess is complete
 
-        process = multiprocessing.Process(
-            target=convert_unsafe,
-            args=(self.neutron_converter, tflite_model, cctx, queue),
-        )
-        process.start()
-        process.join()  # waits until the subprocess is complete
+            if queue.empty():  # signals the unsafe task did not run till the end
+                raise RuntimeError(
+                    f"Neutron converter module terminated unexpectedly with exit code {process.exitcode}"
+                )
 
-        if queue.empty():  # signals the unsafe task did not run till the end
-            raise RuntimeError(
-                f"Neutron converter module terminated unexpectedly with exit code {process.exitcode}"
+            model_converted = queue.get()
+            process.close()
+        except (EOFError, OSError) as e:
+            # Multiprocessing failed (likely due to environment restrictions)
+            # Fall back to direct execution
+            logging.warning(
+                f"Multiprocessing not available ({e}), running neutron converter directly"
+            )
+            model_converted = self.neutron_converter.convertModel(
+                list(tflite_model), cctx
             )
 
-        model_converted = queue.get()
-
-        process.close()
         return bytes(model_converted)