Add base_directory to Python empty mode tests

Empty mode requires base_directory to avoid falling back to ~/.copilot.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: MackinnonBuck

python/test_client.py

@@ -1061,7 +1061,11 @@ class TestMcpOAuthTokenStorage:
     async def test_create_session_defaults_mcp_oauth_token_storage_to_in_memory_in_empty_mode(
         self,
     ):
-        client = CopilotClient(connection=RuntimeConnection.for_stdio(path=CLI_PATH), mode="empty")
+        client = CopilotClient(
+            connection=RuntimeConnection.for_stdio(path=CLI_PATH),
+            mode="empty",
+            base_directory="/tmp/copilot-test",
+        )
         await client.start()
 
         try:
@@ -1106,7 +1110,11 @@ async def mock_request(method, params, **kwargs):
 
     @pytest.mark.asyncio
     async def test_create_session_forwards_explicit_mcp_oauth_token_storage(self):
-        client = CopilotClient(connection=RuntimeConnection.for_stdio(path=CLI_PATH), mode="empty")
+        client = CopilotClient(
+            connection=RuntimeConnection.for_stdio(path=CLI_PATH),
+            mode="empty",
+            base_directory="/tmp/copilot-test",
+        )
         await client.start()
 
         try:
@@ -1131,7 +1139,11 @@ async def mock_request(method, params, **kwargs):
     async def test_resume_session_defaults_mcp_oauth_token_storage_to_in_memory_in_empty_mode(
         self,
     ):
-        client = CopilotClient(connection=RuntimeConnection.for_stdio(path=CLI_PATH), mode="empty")
+        client = CopilotClient(
+            connection=RuntimeConnection.for_stdio(path=CLI_PATH),
+            mode="empty",
+            base_directory="/tmp/copilot-test",
+        )
         await client.start()
 
         try:
@@ -1161,7 +1173,11 @@ async def mock_request(method, params, **kwargs):
 
     @pytest.mark.asyncio
     async def test_resume_session_forwards_explicit_mcp_oauth_token_storage(self):
-        client = CopilotClient(connection=RuntimeConnection.for_stdio(path=CLI_PATH), mode="empty")
+        client = CopilotClient(
+            connection=RuntimeConnection.for_stdio(path=CLI_PATH),
+            mode="empty",
+            base_directory="/tmp/copilot-test",
+        )
         await client.start()
 
         try: