xAI Grok OAuth (and Spotify) use a loopback redirect to
``http://127.0.0.1:<port>/callback`` to capture the authorization
code. That works when the browser and Hermes run on the same
machine, and the SSH tunnel recipe handles the regular remote
case. It breaks completely on **browser-only remote consoles**
(GCP Cloud Shell, GitHub Codespaces, AWS EC2 Instance Connect,
Gitpod, Replit, …) where the user has a browser but no real SSH
client to forward a port — the redirect to 127.0.0.1 on the
remote VM simply isn't reachable from the laptop, and there's
nothing the existing flow can do about it (#26923).
This commit adds the foundation for a manual-paste fallback:
* ``_is_remote_session`` now also recognises Cloud Shell,
Codespaces, Gitpod, Replit, StackBlitz (in addition to SSH),
so the existing tunnel hint at least fires in those
environments.
* ``_parse_pasted_callback`` accepts any of: a full
``http(s)://...?code=...&state=...`` URL, a bare ``?code=...``
query string, a bare ``code=...&state=...`` fragment, or a
bare opaque code value. Returns the same dict shape the HTTP
callback handler produces, so the caller's state / error
validation works unchanged (no CSRF bypass).
* ``_prompt_manual_callback_paste`` reads stdin with a clear
multi-line explanation of what's happening and what to paste.
* ``_xai_oauth_loopback_login`` gains a ``manual_paste`` kwarg
that skips the HTTP listener entirely. The redirect_uri,
PKCE verifier, state, and nonce are byte-identical to the
loopback path so xAI's token endpoint can't tell the
difference at the protocol level.
* ``_print_loopback_ssh_hint`` now also mentions
``--manual-paste`` so users without a real SSH client see a
path forward instead of a dead-end tunnel recipe.
* ``_login_xai_oauth`` threads ``args.manual_paste`` into the
loopback helper.
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