test: consolidate duplicate backend contracts and strengthen stage checks

tests/unit_tests/plugin/test_connector_pure.py

@@ -147,13 +147,6 @@ class TestParsePluginId:
         assert author == 'myauthor'
         assert name == 'myplugin'
 
-    def test_parse_plugin_id_empty(self):
-        """Empty plugin ID is invalid."""
-        from langbot.pkg.plugin.connector import PluginRuntimeConnector
-
-        with pytest.raises(ValueError):
-            PluginRuntimeConnector._parse_plugin_id('')
-
 
 @pytest.mark.asyncio
 async def test_marketplace_response_reader_is_bounded():

tests/unit_tests/plugin/test_plugin_id_parsing.py

@@ -5,10 +5,6 @@ import pytest
 from langbot.pkg.plugin.connector import PluginRuntimeConnector
 
 
-def test_parse_plugin_id_accepts_author_name():
-    assert PluginRuntimeConnector._parse_plugin_id('langbot/rag-engine') == ('langbot', 'rag-engine')
-
-
 @pytest.mark.parametrize(
     'plugin_id',
     [