The CLI hangs on a long request, or retries again and again with no clear error.
What it actually was
Gemini CLI gave a response 60 seconds to start sending headers. Hard Gemini 4 Argon requests can take longer, so it gave up and retried: UND_ERR_HEADERS_TIMEOUT.
What to do
Look for UND_ERR_HEADERS_TIMEOUT in the console before you blame quota, an outage or prompt size. Raising the allowance to 15 minutes for Argon requests fixed the session.