The generic /v1/models probe in validate_requested_model() sent a plain
'Authorization: Bearer <key>' header, which works for OpenAI-compatible
endpoints but results in a 401 Unauthorized from Anthropic's API.
Anthropic requires x-api-key + anthropic-version headers (or Bearer for
OAuth tokens from Claude Code).
Add a provider-specific branch for normalized == 'anthropic' that calls
the existing _fetch_anthropic_models() helper, which already handles
both regular API keys and Claude Code OAuth tokens correctly. This
mirrors the pattern already used for openai-codex, copilot, and bedrock.
The branch also includes:
- fuzzy auto-correct (cutoff 0.9) for near-exact model ID typos
- fuzzy suggestions (cutoff 0.5) when the model is not listed
- graceful fall-through when the token cannot be resolved or the
network is unreachable (accepts with a warning rather than hard-fail)
- a note that newer/preview/snapshot model IDs can be gate-listed
and may still work even if not returned by /v1/models
Fixes Anthropic provider users seeing 'service unreachable' errors
when running /model <claude-model> because every probe 401'd.
2303dd8686