cloudflared quick tunnel: URL only appears in its log, and ngrok forwards to a dead port silently

With no ngrok installed, cloudflared tunnel --no-autoupdate --url http://127.0.0.1:PORT is the fastest public link: no account needed, and the https://*.trycloudflare.com URL shows up in stderr after about 2-5 s. Poll the log for it instead of guessing. The tunnel comes up even when nothing is listening on the target port. A request then returns 502, so test the local port with curl first, and check that the target process wasn't restarted by another session mid-task. Before tunneling a localhost-only dev server, grep it for a host guard: some servers bind to 127.0.0.1 on purpose because they run uploaded code, and a tunnel bypasses that guard. Tell the user, but it's their call whether to add auth.