fix: only use manual SelectorEventLoop on Windows

The hand-constructed SelectorEventLoop path was incompatible with older
uvicorn on Python 3.14 (lowest-direct CI matrix). On non-Windows, defer
to uvicorn's own server.run() which handles loop setup portably. The
selector-loop workaround is only needed on Windows where the default
ProactorEventLoop leaves transports unclosed at thread teardown.

Author: maxisbey

tests/test_helpers.py

@@ -18,19 +18,24 @@
 
 
 def _run_server_in_loop(server: uvicorn.Server) -> None:
-    """Thread target: run uvicorn on a fresh event loop, ensuring clean teardown.
+    """Thread target: run uvicorn with a clean-teardown event loop.
 
     On Windows the default ProactorEventLoop can leave pipe transports alive
     when the loop is destroyed in a background thread — their ``__del__`` fires
     later and pytest's unraisable-exception hook attributes it to the next test.
-    The selector loop shuts down cleanly, so we use it here instead of letting
-    ``server.run()`` call ``asyncio.run()`` with whatever the platform default is.
+    The selector loop shuts down cleanly, so we use it there. On other platforms
+    we defer to ``server.run()`` — uvicorn's own loop setup is more portable
+    across versions than a hand-constructed loop.
     """
-    loop = asyncio.SelectorEventLoop()
-    try:
-        loop.run_until_complete(server.serve())
-    finally:
-        loop.close()
+    if sys.platform == "win32":  # pragma: no cover
+        # Force selector loop without touching process-global policy
+        loop = asyncio.SelectorEventLoop()
+        try:
+            loop.run_until_complete(server.serve())
+        finally:
+            loop.close()
+    else:
+        server.run()
 
 
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