fix: Kimi /coding/v1 — api_mode detection, API key fallback, User-Agent header

[xiaoqiang243]

Summary

Adds User-Agent claude-code/0.1.0 header for Kimi /coding endpoint requests.

Problem

Kimi's /coding/v1/messages endpoint returns 403 unless the User-Agent header is set to claude-code/0.1.0. The existing _requires_bearer_auth() check matches api.kimi.com/coding before our User-Agent injection code is reached, causing kimi-2.5 and kimi-for-coding models to fail with 404/403 errors.

Solution

• Add _is_kimi_coding_endpoint() function to detect Kimi coding API base URLs
• Place Kimi check BEFORE _requires_bearer_auth() in build_anthropic_client() so the User-Agent header is correctly injected
• kimi-2.5, kimi-for-coding, and kimi-k2.6-code-preview all verified working via SDK

Testing

All three Kimi coding models tested and confirmed working:

• kimi-2.5: ~0.9s response
• kimi-for-coding: ~1.0s response
• kimi-k2.6-code-preview: ~1.7s response

[teknium1]

Merged via #13782 — your commits were cherry-picked onto current main with your authorship preserved in git log (commits de181df, fd40385, bad5471, 46d6801, 2a026eb, 6caf8bd).

Thanks for the fix @xiaoqiang243! I added two follow-up commits on top:

• KIMI_CODE_BASE_URL needed to drop its /v1 suffix — the Anthropic SDK appends /v1/messages internally, so /coding/v1 + SDK suffix produced /coding/v1/v1/messages (404). Using /coding yields the correct /coding/v1/messages.
• Preserved the kimi-coding default inference_base_url as api.moonshot.ai/v1 so legacy Moonshot keys still authenticate — only sk-kimi- prefixed keys get redirected (via the existing _resolve_kimi_base_url).

E2E verified both sk-kimi- and legacy sk- paths with real imports and httpx MockTransport.

[alt-glitch]

Likely superseded by #13782 (merged) — same Kimi Coding endpoint fix with broader scope.