test(companion): Add control command tests

Wire ControlServer.handle_line to a real CompanionManager.handle_command and
assert the full decode/dispatch/encode round trip: status returns the companion
list, start routes through and reports a message, and unknown command, missing
name, and reread without a loader each return an error envelope.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/design/companion-process-manager.md

@@ -697,7 +697,7 @@ No per-companion logic in Arbiter.
 - [x] Add lifecycle logs.
 - [x] Add tests for config validation.
 - [x] Add tests for state transitions.
-- [ ] Add tests for control commands.
+- [x] Add tests for control commands.
 - [ ] Add tests for transactional reread.
 - [ ] Add tests that HTTP worker behavior is unchanged.
 

tests/test_companion_control.py

@@ -7,12 +7,23 @@ from unittest import mock
 
 import pytest
 
+from gunicorn.companion.config import CompanionConfig
 from gunicorn.companion.control import (
     CommandError,
     ControlServer,
     decode_command,
     encode_response,
 )
+from gunicorn.companion.manager import CompanionManager
+
+
+def make_manager(*names):
+    configs = [CompanionConfig(name=name, target=lambda: None) for name in names]
+    return CompanionManager(configs, log=mock.Mock())
+
+
+def server_for(manager):
+    return ControlServer(dispatch=manager.handle_command, path="/tmp/x.sock")
 
 
 def test_decode_command_valid():
@@ -85,3 +96,41 @@ def test_close_unlinks():
         server.close()
     unlink.assert_called_once_with("/tmp/x.sock")
     assert server.listener is None
+
+
+def test_control_status_command_end_to_end():
+    manager = make_manager("rq")
+    response = json.loads(server_for(manager).handle_line('{"cmd": "status"}'))
+    assert response["ok"] is True
+    assert response["companions"][0]["name"] == "rq"
+
+
+def test_control_start_command_end_to_end():
+    manager = make_manager("rq")
+    with mock.patch("os.fork", return_value=10):
+        response = json.loads(
+            server_for(manager).handle_line('{"cmd": "start", "name": "rq"}'))
+    assert response["ok"] is True
+    assert "rq" in response["message"]
+
+
+def test_control_unknown_command_error_envelope():
+    manager = make_manager("rq")
+    response = json.loads(
+        server_for(manager).handle_line('{"cmd": "bogus", "name": "rq"}'))
+    assert response["ok"] is False
+    assert "unknown" in response["error"]
+
+
+def test_control_missing_name_error_envelope():
+    manager = make_manager("rq")
+    response = json.loads(server_for(manager).handle_line('{"cmd": "start"}'))
+    assert response["ok"] is False
+    assert "name" in response["error"]
+
+
+def test_control_reread_without_loader_error_envelope():
+    manager = make_manager("rq")
+    response = json.loads(server_for(manager).handle_line('{"cmd": "reread"}'))
+    assert response["ok"] is False
+    assert "reread" in response["error"]