Set .base to self for reference returns, verify in tests

Fixed the .base attribute handling as requested:
- For reference returns: Explicitly set (<numpy.ndarray>arr).base = self to keep owner alive
- For value returns: ArrayWrapper automatically set as .base by buffer protocol (already working)
- Updated test to verify .base is the owner object (not memoryview)

This ensures proper lifetime management - the numpy array keeps the C++ object alive to prevent premature garbage collection.

Commit addresses comment 3679292583

Co-authored-by: jpfeuffer <8102638+jpfeuffer@users.noreply.github.com>

Author: Copilot

autowrap/ConversionProvider.py

@@ -2248,8 +2248,7 @@ def output_conversion(
             if cpp_type.is_ref:
                 # Reference return: Use Cython memory view for zero-copy access
                 # For const references: set readonly flag
-                # The memory view object automatically becomes the base when we call numpy.asarray()
-                # We need to ensure 'self' (the owner) is kept alive by the memory view
+                # Explicitly set .base to self to keep the owner alive (not the memory view)
                 if cpp_type.is_const:
                     code = Code().add(
                         """
@@ -2258,6 +2257,7 @@ def output_conversion(
                         |cdef $ctype[:] _view_$output_py_var = <$ctype[:_size_$output_py_var]>$input_cpp_var.data()
                         |cdef object $output_py_var = numpy.asarray(_view_$output_py_var)
                         |$output_py_var.setflags(write=False)
+                        |(<numpy.ndarray>$output_py_var).base = self
                         """,
                         dict(
                             input_cpp_var=input_cpp_var,
@@ -2272,6 +2272,7 @@ def output_conversion(
                         |cdef size_t _size_$output_py_var = $input_cpp_var.size()
                         |cdef $ctype[:] _view_$output_py_var = <$ctype[:_size_$output_py_var]>$input_cpp_var.data()
                         |cdef object $output_py_var = numpy.asarray(_view_$output_py_var)
+                        |(<numpy.ndarray>$output_py_var).base = self
                         """,
                         dict(
                             input_cpp_var=input_cpp_var,

tests/test_files/numpy_vector/numpy_vector_wrapper.pyx

@@ -743,6 +743,7 @@ cdef class NumpyVectorTest:
         cdef double[:] _view_py_result = <double[:_size_py_result]>_r.data()
         cdef object py_result = numpy.asarray(_view_py_result)
         py_result.setflags(write=False)
+        (<numpy.ndarray>py_result).base = self
         return py_result
 
     def getMutableRefVector(self):
@@ -754,6 +755,7 @@ cdef class NumpyVectorTest:
         cdef size_t _size_py_result = _r.size()
         cdef double[:] _view_py_result = <double[:_size_py_result]>_r.data()
         cdef object py_result = numpy.asarray(_view_py_result)
+        (<numpy.ndarray>py_result).base = self
         return py_result
 
     def getValueVector(self,  size ):

tests/test_numpy_vector_converter.py

@@ -74,9 +74,10 @@ def test_const_ref_output_is_readonly_view(self, numpy_vector_module):
         with pytest.raises(ValueError, match="read-only"):
             result[0] = 999.0
 
-        # Check base attribute - should be the C++ object or a memory view wrapper
-        # Memory views keep a reference to the owner to prevent garbage collection
+        # Check base attribute - should be the C++ object (NumpyVectorTest instance)
+        # This keeps the owner alive to prevent garbage collection
         assert result.base is not None
+        assert result.base is t, f"Expected .base to be the NumpyVectorTest instance, got {type(result.base).__name__}"
 
     @pytest.mark.skip(reason="Mutable ref views require ensuring C++ object lifetime exceeds view lifetime - needs investigation of reference handling")
     def test_mutable_ref_output_is_view(self, numpy_vector_module):