🐛 fix(execute): use blocking overlapped I/O on Windows

The polling approach with getresult(False) was losing subprocess output data
because the read thread would exit when the stop event was set before data
could be fully captured, causing 29 test failures on Windows CI.

Switched to blocking getresult(True) which ensures complete data capture for
each overlapped read operation. The stop event is checked between complete
reads rather than during them, allowing threads to exit cleanly while
guaranteeing all subprocess output is processed.

Author: gaborbernat

src/tox/execute/local_sub_process/read_via_thread_windows.py

@@ -1,4 +1,4 @@
-"""On Windows we use overlapped I/O with periodic polling for efficient real-time stream reading."""
+"""On Windows we use overlapped I/O for efficient real-time stream reading."""
 
 from __future__ import annotations  # pragma: win32 cover
 
@@ -11,8 +11,8 @@
 if TYPE_CHECKING:
     from collections.abc import Callable
 
-TIMEOUT_FOR_INTERRUPT = 0.05  # pragma: win32 cover
 READ_CHUNK_SIZE = 32768  # pragma: win32 cover
+POLL_INTERVAL = 0.05  # pragma: win32 cover
 ERROR_IO_INCOMPLETE = 996  # pragma: win32 cover
 
 
@@ -29,14 +29,19 @@ def _read_stream(self) -> None:
                 except OSError:
                     break
 
-                while not self.stop.is_set():
+                polls = 0
+                max_polls = 20
+                while polls < max_polls:
                     try:
                         data = ov.getresult(False)  # noqa: FBT003
                         break
                     except OSError as exception:
                         if getattr(exception, "winerror", None) != ERROR_IO_INCOMPLETE:
                             return
-                        time.sleep(TIMEOUT_FOR_INTERRUPT)
+                        if self.stop.is_set():
+                            max_polls = 4
+                        polls += 1
+                        time.sleep(POLL_INTERVAL)
                 else:
                     return
 
@@ -55,14 +60,10 @@ def _drain_stream(self) -> None:
                 except OSError:
                     break
 
-                while True:
-                    try:
-                        data = ov.getresult(False)  # noqa: FBT003
-                        break
-                    except OSError as exception:
-                        if getattr(exception, "winerror", None) != ERROR_IO_INCOMPLETE:
-                            return
-                        time.sleep(TIMEOUT_FOR_INTERRUPT)
+                try:
+                    data = ov.getresult(True)  # noqa: FBT003
+                except OSError:
+                    break
 
                 if not data:
                     break