translator: handle numeric OpenAI error.code in Anthropic→OpenAI error translation

[Copilot]

Description

Anthropic→OpenAI error translation could fail with an internal 500 when an OpenAI-compatible upstream returned a structured JSON error where error.code was numeric (e.g. 400) instead of string. This change makes the error model tolerant to both representations so upstream 4xx diagnostics can still be translated and surfaced to Anthropic clients.

• Schema decoding hardening (internal/apischema/openai/openai.go)

  • Added UnmarshalJSON for openai.ErrorType.
  • error.code now accepts:
    • JSON string ("code":"400")
    • JSON number ("code":400)
    • null / omitted
  • Numeric values are normalized to the existing internal *string field.

• Translator regression coverage (internal/translator/anthropic_openai_test.go)

  • Extended TestAnthropicToOpenAITranslator_ResponseError with a JSON error fixture containing numeric code.
  • Confirms response still maps to Anthropic error envelope with expected type and message.

{
  "type": "error",
  "error": {
    "type": "invalid_request_error",
    "message": "Bad request",
    "param": null,
    "code": 400
  }
}

Related Issues/PRs (if applicable)

Fixes #2151

Special notes for reviewers (if applicable)

N/A

[nacx]

@copilot fix the failing checks by setting a proper PR title and description according to the check requirements.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 70.37037% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.71%. Comparing base (2bb3904) to head (bd4b5bc).

Files with missing lines	Patch %	Lines
internal/apischema/openai/openai.go	70.37%	7 Missing and 1 partial ⚠️

❌ Your patch status has failed because the patch coverage (70.37%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2161      +/-   ##
==========================================
- Coverage   84.73%   84.71%   -0.02%     
==========================================
  Files         144      144              
  Lines       21134    21161      +27     
==========================================
+ Hits        17908    17927      +19     
- Misses       2145     2152       +7     
- Partials     1081     1082       +1     

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[Copilot]

@copilot fix the failing checks by setting a proper PR title and description according to the check requirements.

I checked the failing PR Style jobs: they require a Conventional Commit PR title and a PR description whose first line is exactly **Description**. I can’t directly edit PR metadata from this environment. Please update the PR title to something like fix(translator): handle numeric OpenAI error.code in Anthropic→OpenAI error translation and update the description to start with **Description** (with no template comments).

[nacx]

/retest