ROADMAP "Backend → more tests around endpoint probing and provider setup"
and the "Provider setup/probing audit" item. test_provider_endpoints.py
covers URL/header building; this adds the provider-identification and
degraded-state error reporting around it, against the real src.llm_core:
- _detect_provider: host-based (not substring) provider matching, with
look-alike-host and domain-in-path guards, and the OpenAI-compatible
fallback that xAI / DeepSeek / Gemini correctly use.
- _provider_label: human names used in error messages (incl. native vs
cloud Ollama and the generic local-endpoint case).
- _format_upstream_error: 401/403/404/429/5xx → provider-aware sentences,
with JSON / string / plain-text / bytes body detail extraction.
- _uses_max_completion_tokens: gpt-5 / o-series detection (gpt-4o stays
on plain max_tokens).
