Previously only base64 data: URLs were handled in the OpenAI-to-Claude
and OpenAI-to-Gemini request translators. HTTP/HTTPS image URLs were
silently dropped, causing vision-capable models to respond with
"I don't see any image."
Change Codex test from token-expiry-only check to probing the real
Codex API endpoint. Sends a minimal request body that triggers a fast
400 without consuming quota. A 400 confirms auth works; only 401/403
indicates a bad token.
Also adds generic acceptStatuses support to the OAuth test framework
so other providers can define non-200 success statuses.
When a provider has credentials but all are disabled, return 404 (NOT_FOUND)
instead of 400 (BAD_REQUEST). The combo handler already treats 404 as a
fallbackable error, so it will skip to the next model in the chain.
Previously, the 400 status caused the combo to stop with a hard error,
killing the client (e.g., Claude Code) even though other models in the
combo chain were available.
Also changed log level from error to warn since disabled credentials
are an expected configuration state, not an error.
Fixes#334
Ryan