fix(tui): harden themes and platform coverage

tests/cli/test_commands.py

@@ -1565,6 +1565,15 @@ def test_agent_help_shows_workspace_and_config_options():
     assert "-w" in stripped_output
     assert "--config" in stripped_output
     assert "-c" in stripped_output
+    assert "--theme" in stripped_output
+
+
+def test_agent_rejects_unknown_tui_theme(mock_agent_runtime):
+    result = runner.invoke(app, ["agent", "-m", "hello", "--theme", "sepia"])
+
+    assert result.exit_code != 0
+    assert "must be auto, dark, or light" in result.output
+    mock_agent_runtime["from_config"].assert_not_called()
 
 
 def test_agent_uses_default_config_when_no_workspace_or_config_flags(mock_agent_runtime):

tests/cli/test_tui_launcher.py

@@ -73,6 +73,7 @@ def test_interactive_agent_uses_native_tui(
         markdown=True,
         logs=False,
         classic=False,
+        theme="light",
     )
 
     assert launched["args"] == (config,)
@@ -80,6 +81,7 @@ def test_interactive_agent_uses_native_tui(
         "config_path": config_path,
         "workspace_override": None,
         "session_id": "websocket:terminal-chat",
+        "theme": "light",
     }