control: both real servers answering, empty isolated state
{"host": "B", "status": 200, "projects": 0, "threads": 0, "elapsed_ms": 35}
{"host": "A", "status": 200, "projects": 0, "threads": 0, "elapsed_ms": 38}
passive B: TCP listener accepts connections but sends no HTTP response
{"host": "A", "status": 200, "projects": 0, "threads": 0, "elapsed_ms": 8}
{"host": "B", "error": "TimeoutError", "elapsed_ms": 6008}
passive B: port closed (connection refused)
{"host": "B", "error": "URLError", "elapsed_ms": 1}
{"host": "A", "status": 200, "projects": 0, "threads": 0, "elapsed_ms": 6}