test(plugins): add runner-level regression for plugin failure during on_run_error_callback

Adds end-to-end test through Runner.run_async() verifying that a crashing
on_run_error_callback plugin does not mask the original application exception.
Symmetric with the existing agent-level test.

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

Author: caohy1988

tests/unittests/plugins/test_error_callbacks.py

@@ -569,3 +569,46 @@ async def on_agent_error_callback(self, **kwargs):
     # NOT the plugin's ValueError.
     with pytest.raises(RuntimeError, match="agent crashed"):
       _ = [e async for e in agent.run_async(ctx)]
+
+  @pytest.mark.asyncio
+  async def test_original_exception_propagates_despite_run_plugin_failure(
+      self,
+  ):
+    """End-to-end: a crashing plugin on_run_error_callback does not mask
+    the original agent exception seen by the runner caller."""
+    from google.adk.runners import Runner
+
+    class _FailingRunPlugin(BasePlugin):
+      __test__ = False
+
+      def __init__(self, name):
+        super().__init__(name)
+
+      async def on_run_error_callback(self, **kwargs):
+        raise ValueError("plugin internal error")
+
+    plugin = _FailingRunPlugin(name="bad_plugin")
+    agent = _CrashingAgent(name="crash_agent")
+    runner = Runner(
+        agent=agent,
+        app_name="test_app",
+        session_service=InMemorySessionService(),
+        plugins=[plugin],
+    )
+    session = await runner.session_service.create_session(
+        app_name="test_app", user_id="test_user"
+    )
+
+    # The caller must see the original RuntimeError("agent crashed"),
+    # NOT the plugin's ValueError.
+    with pytest.raises(RuntimeError, match="agent crashed"):
+      _ = [
+          e
+          async for e in runner.run_async(
+              user_id="test_user",
+              session_id=session.id,
+              new_message=types.Content(
+                  parts=[types.Part(text="hello")]
+              ),
+          )
+      ]