fix(plugins): bound async plugin command await with 30s timeout

Follow-up to #17963. The threaded branch of resolve_plugin_command_result
previously called Event.wait() with no timeout — a hung async plugin
handler would wedge the terminal indefinitely. Cap the wait at 30s and
raise TimeoutError instead. Added a regression test covering the hung
handler path.

tests/hermes_cli/test_plugins.py

@@ -1082,6 +1082,24 @@ class TestPluginCommandResultResolution:
         monkeypatch.setattr("hermes_cli.plugins.asyncio.get_running_loop", lambda: _Loop())
         assert resolve_plugin_command_result(_handler()) == "threaded-ok"
 
+    def test_running_loop_timeout_does_not_hang_forever(self, monkeypatch):
+        """Threaded path must abort a hung async handler instead of blocking the caller."""
+        import asyncio as _asyncio
+
+        class _Loop:
+            pass
+
+        async def _slow_handler():
+            await _asyncio.sleep(10)
+            return "should-not-reach"
+
+        monkeypatch.setattr("hermes_cli.plugins.asyncio.get_running_loop", lambda: _Loop())
+        monkeypatch.setattr("hermes_cli.plugins._PLUGIN_COMMAND_AWAIT_TIMEOUT_SECS", 0.1)
+
+        import pytest
+        with pytest.raises(TimeoutError):
+            resolve_plugin_command_result(_slow_handler())
+
 
 # ── TestPluginDispatchTool ────────────────────────────────────────────────