Fix 15-second close delay after dialog tests

Dialog subprocesses were forked from TestProcess, inheriting its
multiprocessing Queue objects and their process-shared POSIX semaphores
(_wlock). If a fork happened while the feeder thread held _wlock, the
child exited without releasing it, permanently blocking the feeder
thread on the next wacquire() and stalling Python's atexit _finalize_join
— causing test_proc.join() (no timeout) to hang the app for ~15 seconds.

Fix: use multiprocessing.get_context('spawn') for dialog subprocesses so
they start with a clean interpreter and inherit no semaphores or Queue
state. Also add a terminate/kill fallback timeout to test_proc.join() as
a safety net, and fix the missing return in JsonRpcConnection.is_alive().

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/lib/jrpc.py

@@ -228,7 +228,7 @@ class JsonRpcConnection:
         self.recv_thread.join()
 
     def is_alive(self):
-        self.recv_thread.is_alive()
+        return self.recv_thread.is_alive()
 
     def wait_ready(self, timeout=None):
         return self._event_ready.wait(timeout)

src/testium/interpreter/test_items/test_item_dialog_base.py

@@ -1,7 +1,9 @@
-from multiprocessing import Process, Pipe
+import multiprocessing
 
 from interpreter.test_items.test_item import TestItem
 
+_spawn_ctx = multiprocessing.get_context('spawn')
+
 
 class TestItemDialogBase(TestItem):
     """Base class for test items that launch a Qt dialog in a subprocess."""
@@ -19,7 +21,7 @@ class TestItemDialogBase(TestItem):
 
         Returns the subprocess exit code.
         """
-        p = Process(target=target, args=(args,))
+        p = _spawn_ctx.Process(target=target, args=(args,))
         p.start()
         while p.is_alive() and not self._is_stopped:
             p.join(timeout=0.5)
@@ -31,9 +33,10 @@ class TestItemDialogBase(TestItem):
 
         Returns the received value, or None if stopped or if the subprocess crashed.
         """
-        parent_conn, child_conn = Pipe()
+        parent_conn, child_conn = _spawn_ctx.Pipe()
-        p = Process(target=target, args=(args, child_conn))
+        p = _spawn_ctx.Process(target=target, args=(args, child_conn))
         p.start()
+        child_conn.close()
         result = None
         while p.is_alive() and not self._is_stopped:
             if parent_conn.poll(0.5):

src/testium/main_win/test_file_manager.py

@@ -30,7 +30,13 @@ class TestFileManager:
         ):
             w.test_service.stop()
             w.test_service.close()
-            w.test_proc.join()
+            w.test_proc.join(timeout=5)
+            if w.test_proc.is_alive():
+                w.test_proc.terminate()
+                w.test_proc.join(timeout=2)
+            if w.test_proc.is_alive():
+                w.test_proc.kill()
+                w.test_proc.join()
             del w.test_proc
             w.test_proc = None
             del w.test_service