lib.App: Restore previous event loop in run()

When run() creates an event loop, it installs it with
set_event_loop() but never restores the thread's previous loop, so
after run() returns, the thread is left with the now-closed loop
created by run(). Any code that calls get_event_loop() afterwards
gets a closed loop, and on Python 3.13+ a thread that had no loop at
all starts emitting or raising deprecation errors that run() caused.

Capture the thread's current loop with _get_current_event_loop()
before installing a new one, and restore it in the finally block. If
there was no previous loop, unset the loop with set_event_loop(None)
so that the thread is left without a loop instead of with the closed
one.

Assisted-by: unsloth/Qwen3.8-27B-GGUF:Q4_K_M with pi.dev v0.84.2
Signed-off-by: Jan Lindemann <jan@janware.com>

src/python/jw/pkg/lib/App.py

@@ -4,6 +4,7 @@ import asyncio
 import cProfile
 import os
 import sys
+import warnings
 
 from argparse import ArgumentDefaultsHelpFormatter, ArgumentParser, Namespace
 from typing import TYPE_CHECKING, Any, cast, override
@@ -31,6 +32,17 @@ if TYPE_CHECKING:
     from typing import TypeVar
     T = TypeVar('T')
 
+def _get_current_event_loop() -> asyncio.AbstractEventLoop | None:
+    """Return the current event loop of this thread, or None if there is
+    none, without creating one implicitly or emitting a deprecation
+    warning."""
+    with warnings.catch_warnings():
+        warnings.simplefilter('error', DeprecationWarning)
+        try:
+            return asyncio.get_event_loop()
+        except (RuntimeError, DeprecationWarning):
+            return None
+
 class App:  # export
 
     def _add_arguments(self, parser: ArgumentParser) -> None:
@@ -341,7 +353,9 @@ class App:  # export
         return self.__parser
 
     def run(self, argv: list[str] | None = None) -> None:
+        previous_eloop: asyncio.AbstractEventLoop | None = None
         if self.__eloop is None:
+            previous_eloop = _get_current_event_loop()
             eloop = asyncio.new_event_loop()
             asyncio.set_event_loop(eloop)
             self.__eloop = eloop
@@ -350,6 +364,12 @@ class App:  # export
             ret = self.eloop.run_until_complete(self.__run(argv))
         finally:
             self.close()
+            # -- Restore the event loop the thread had before run(), or
+            # unset the loop if there was none.
+            if previous_eloop is not None:
+                asyncio.set_event_loop(previous_eloop)
+            else:
+                asyncio.set_event_loop(None)
         return ret