A config left with `provider: anthropic` but a leftover
`base_url: https://openrouter.ai/api/v1` (e.g. after a provider switch)
would route Anthropic OAuth/setup-token traffic to OpenRouter and 404.
Add `_anthropic_base_url_override_ok()` and gate the three native-Anthropic
resolution branches (pool, explicit, native) on it. The guard honors a
configured `model.base_url` only when it plausibly speaks the Anthropic
Messages protocol — official `*.anthropic.com` / `*.claude.com` hosts, Azure
Foundry endpoints, and `/anthropic`-suffixed or Kimi `/coding` proxies — and
falls back to `https://api.anthropic.com` otherwise. Aggregator URLs like
openrouter.ai / api.openai.com are treated as stale.
Reconstructed from @clovericbot's PR #3661 onto current main: the original
patched one branch with an anthropic-only allow-list, which would have broken
Azure-via-anthropic; widened to all three sites and made Azure/proxy-safe.
奥森木
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