xAI's consent page renders the authorization code in-page rather than
redirecting through the 127.0.0.1 callback, so on remote/headless setups
(GCP Cloud Shell, Codespaces, container consoles, headless VPS) the only
value the user can paste is the opaque code with no `code=`/`state=`
query parameters. `_parse_pasted_callback` correctly returns
`state=None` for that input, but `_xai_oauth_loopback_login` then
validated state unconditionally and raised `xai_state_mismatch`,
making the documented bare-code paste path unreachable.
PKCE (code_verifier) still binds the token exchange to this client,
so the local state-equality check is redundant when there is no state
to compare. On the manual-paste path only, substitute the locally
generated state when the callback returned none — the rest of the
validation chain (code presence, error field, token exchange) is
unchanged. The loopback HTTP-server path still requires a matching
state (a real browser redirect always carries one).
Also: clarify the manual-paste prompt to mention xAI's in-page code
rendering so users know pasting the bare code on its own is expected.
Root-cause analysis from #26923 comment by @AccursedGalaxy (2026-05-20).
Tests
-----
* test_xai_loopback_login_manual_paste_bare_code_succeeds — positive
end-to-end through the token exchange with state=None.
* test_xai_loopback_login_loopback_path_rejects_missing_state — the
HTTP-server path still rejects state=None as a regression guard
(the bare-code relaxation must NOT widen the loopback path).
* Existing test_xai_loopback_login_manual_paste_state_mismatch_raises
continues to verify wrong (non-None) state is rejected on manual-paste.
Closes#26923.
a82c88bac0