cuda.core: treat the NULL stream as a default-stream token

cuda_core/cuda/core/_stream.pyx

@@ -522,13 +522,14 @@ cdef inline bint Stream_handle_is_default_token(cydriver.CUstream s) noexcept no
 
     These tokens carry no context of their own; they refer to whatever context
     is current, so nothing resolved from one may be cached on the object.
+    The NULL stream (handle 0) is such a token too.
     """
     cdef uintptr_t h = <uintptr_t>s
-    return h == <uintptr_t>cydriver.CU_STREAM_LEGACY or h == <uintptr_t>cydriver.CU_STREAM_PER_THREAD
+    return h == 0 or h == <uintptr_t>cydriver.CU_STREAM_LEGACY or h == <uintptr_t>cydriver.CU_STREAM_PER_THREAD
 
 
 cdef inline bint Stream_is_default_token(Stream self) noexcept nogil:
-    """Return True when this stream is CU_STREAM_LEGACY or CU_STREAM_PER_THREAD."""
+    """Return True when this stream is the NULL stream, CU_STREAM_LEGACY or CU_STREAM_PER_THREAD."""
     return Stream_handle_is_default_token(as_cu(self._h_stream))
 
 

cuda_core/docs/source/release/1.3.0-notes.rst

@@ -321,6 +321,13 @@ Fixes and enhancements
   ``repr`` now shows ``U`` for unified operands.
   (`#2649 <https://github.com/NVIDIA/cuda-python/issues/2649>`__)
 
+- A :class:`Stream` over the NULL stream (handle 0), such as
+  ``Stream.from_handle(0)``, no longer caches the first context and device it
+  observes. Like ``LEGACY_DEFAULT_STREAM`` and ``PER_THREAD_DEFAULT_STREAM``
+  since 1.2.0, it now resolves ``Stream.context``, ``Stream.device``,
+  ``Stream.resources`` and ``Stream.record()`` against the current context.
+  (`#3242 <https://github.com/NVIDIA/cuda-python/issues/3242>`__)
+
 Deprecations
 ------------
 

cuda_core/tests/test_green_context.py

@@ -15,6 +15,7 @@
     ProgramOptions,
     SMResource,
     SMResourceOptions,
+    Stream,
     WorkqueueResource,
     WorkqueueResourceOptions,
     launch,
@@ -560,6 +561,17 @@ def test_stream_and_event_track_green_context(self, green_ctx):
         stream.sync()
         event.sync()
 
+    @pytest.mark.agent_authored(model="claude-opus-5-5")
+    def test_null_stream_follows_current_context(self, init_cuda, green_ctx):
+        stream = Stream.from_handle(0)
+        assert stream.context == init_cuda.context
+
+        with use_context(init_cuda, green_ctx):
+            assert stream.context == green_ctx
+            assert stream.record().context == green_ctx
+
+        assert stream.context == init_cuda.context
+
     @pytest.mark.agent_authored(model="gpt-5.6")
     def test_device_receiver_targets_stored_green_context(self, init_cuda, green_ctx):
         primary_ctx = init_cuda.context