docs(provider): clarify MiniMax dual-endpoint auto-switch + regression test

Issue #141 (upstream PR #188) reports that MiniMax China Token Plan
users get 401 authorized_error because the international endpoint is
hit with a Token Plan key. Upstream's fix flips the default
`api_base` from `api.minimax.io` to `api.minimaxi.com`.

Our fork already handles this differently and better: the resolver
(`apply_profile_key_based_endpoint_overrides`) auto-routes any
`sk-cp-*` API key to the China base URL (`MINIMAX_CHINA_API_BASE`)
without changing the default for international users. Mechanically
porting upstream's flip would regress everyone whose key does not
start with `sk-cp-`.

This change:
- Updates OAUTH.md MiniMax section to document the dual-endpoint
  behavior so users see exactly which base URL their key resolves to,
  and explicitly calls out that `sk-cp-...` keys auto-route to
  `api.minimaxi.com`.
- Adds a regression test
  `minimax_token_plan_keys_route_to_china_even_when_openai_api_key_env_is_international`
  that pins down the exact 401 scenario from the issue: an unrelated
  international `OPENAI_API_KEY` exported in env must NOT pull the
  resolution back to `.io` when a real `sk-cp-*` key is the one
  actually being used.

Defaults in `MINIMAX_PROFILE` are intentionally left unchanged.

Refs #141

Author: quangdang46

OAUTH.md

@@ -266,9 +266,19 @@ Two notable presets are:
 - Login: `jcode login --provider minimax`
 - Stored env file: `~/.config/jcode/minimax.env`
 - API key env var: `OPENAI_API_KEY`
-- Base URL: `https://api.minimax.io/v1`
+- Endpoint auto-selection by API key:
+  - **International** (default): `https://api.minimax.io/v1`
+    - Docs: <https://platform.minimax.io/docs/guides/text-generation>
+  - **China Token Plan** (auto-selected when the key starts with `sk-cp-`):
+    `https://api.minimaxi.com/v1`
+    - Docs: <https://platform.minimaxi.com/docs/llms.txt>
 - Default model hint: `MiniMax-M2.7`
-- Docs: <https://platform.minimax.io/docs/guides/text-generation>
+
+> jcode resolves the MiniMax base URL from the API key prefix. China
+> Token Plan keys (`sk-cp-...`) automatically route to
+> `api.minimaxi.com`, so users on the China platform should not see
+> the upstream `401 / authorized_error` reported when the international
+> endpoint is hit with a Token Plan key.
 
 These are first-class jcode provider presets, not just manual custom endpoint examples.
 You can still use `openai-compatible` for arbitrary custom providers when there is not a built-in preset.

src/provider_catalog_tests.rs

@@ -129,6 +129,31 @@ fn minimax_token_plan_keys_resolve_to_china_endpoint_without_changing_internatio
     assert_eq!(china.setup_url, MINIMAX_CHINA_SETUP_URL);
 }
 
+#[test]
+fn minimax_token_plan_keys_route_to_china_even_when_openai_api_key_env_is_international() {
+    // Regression for issue #141 (upstream PR #188): users on the MiniMax
+    // China Token Plan reported a `401 authorized_error` because their
+    // `sk-cp-...` keys were being sent to `api.minimax.io`. Our fork
+    // resolves the base URL from the *hint* (the actual key being used to
+    // call the API), not from a stale `OPENAI_API_KEY` env value, so the
+    // auto-switch must still kick in even when an unrelated international
+    // OpenAI key is exported in the shell.
+    let _lock = crate::storage::lock_test_env();
+    let _guard = EnvGuard::save(&["OPENAI_API_KEY"]);
+    crate::env::set_var("OPENAI_API_KEY", "sk-international-not-china");
+
+    let resolved = resolve_openai_compatible_profile_with_api_key_hint(
+        MINIMAX_PROFILE,
+        Some("sk-cp-real-china-token"),
+    );
+    assert_eq!(
+        resolved.api_base, MINIMAX_CHINA_API_BASE,
+        "sk-cp-* keys must route to api.minimaxi.com regardless of an \
+         unrelated international OPENAI_API_KEY in env"
+    );
+    assert_eq!(resolved.setup_url, MINIMAX_CHINA_SETUP_URL);
+}
+
 #[test]
 fn auth_issue_lan_openai_compatible_bases_are_valid_for_local_model_servers() {
     assert_eq!(