@@ -32,6 +32,7 @@
 from helpers.constants import POOL_SIZE
 from helpers.memory import (
     BaselineMemoryResourceReleasedWarning,
+    MemoryResourceLeakTraceWarning,
     UnreleasedMemoryResourceWarning,
     skip_if_pinned_memory_unsupported,
 )
@@ -165,6 +166,29 @@ def _release_device_default_memory_resources():
         d._memory_resource = None
 
 
+# TEMPORARY DIAGNOSTIC -- drop this helper and its call site before merge.
+def _warn_mr_leak_trace(item, live_at_start, live_at_end, expected_live):
+    """Emit a warning naming any item whose live-MemoryResource count changed.
+
+    pytest always includes the warnings summary in its report output, so this
+    surfaces in the CI log without any workflow changes -- the goal is to pin
+    the Windows-only cross-test leaker (the non-init_cuda item that leaves
+    resources alive and later trips UnreleasedMemoryResourceWarning) to the
+    exact test. Only nonzero deltas are warned about; init_cuda items are
+    tagged so they can be told apart (they self-heal via the teardown gate).
+    """
+    delta = live_at_end - live_at_start
+    if delta == 0:
+        return
+    kind = "init_cuda" if _item_uses_init_cuda(item) else "plain"
+    warnings.warn(
+        f"[mr-leak-trace] {kind} {item.nodeid} live_delta={delta:+d} "
+        f"(start={live_at_start} end={live_at_end} expected={expected_live})",
+        MemoryResourceLeakTraceWarning,
+        stacklevel=2,
+    )
+
+
 @pytest.hookimpl(wrapper=True)
 def pytest_runtest_protocol(item, nextitem):
     # Leftover check: compare with the count after the previous init_cuda test,
@@ -183,6 +207,15 @@ def pytest_runtest_protocol(item, nextitem):
             # Only lower it: a released resource must not hide a later leak.
             _mr_expected_live = min(_mr_expected_live, live)
 
+        # TEMPORARY DIAGNOSTIC -- drop this whole block (and the commit it is
+        # in) before merge. It warns about any item whose live-MemoryResource
+        # count changed, so a Windows-only cross-test leaker (one that trips
+        # UnreleasedMemoryResourceWarning at a later init_cuda test) can be
+        # pinned to the exact non-init_cuda item that left resources alive.
+        # The warning always appears in the pytest warnings summary, so it
+        # surfaces in CI with no workflow changes.
+        _warn_mr_leak_trace(item, _mr_live_at_item_start, live, _mr_expected_live)
+
 
 class _CudaCoreParallelPlugin:
     """A mini pytest plugin used only for pytest-run-parallel testing.
 
@@ -17,6 +17,16 @@ class BaselineMemoryResourceReleasedWarning(Warning):
     """An ``init_cuda`` test released a resource that existed before it started."""
 
 
+# TEMPORARY DIAGNOSTIC -- drop this class and its uses before merge.
+class MemoryResourceLeakTraceWarning(Warning):
+    """Diagnostic: a test changed the live ``MemoryResource`` count.
+
+    Emitted by the ``pytest_runtest_protocol`` hook in ``conftest.py`` to pin
+    the Windows-only cross-test leaker. Not part of the gate; remove with its
+    commit.
+    """
+
+
 def skip_if_pinned_memory_unsupported(device):
     try:
         if not device.properties.host_memory_pools_supported: