fix(vertex): convert Claude format request for Gemini models in Verte…

[togawa-sakiko]

Problem

When routing a Claude-format request (/v1/messages) through a Vertex channel with a Gemini model, the request was sent to the Gemini endpoint still in Anthropic format, causing an error.

Root Cause

ConvertClaudeRequest in the Vertex adaptor always returned the request as Anthropic format (via copyRequest), regardless of RequestMode. It lacked the RequestModeGemini branch that ConvertOpenAIRequest already handles correctly.

Fix

Add a RequestModeGemini branch in ConvertClaudeRequest that delegates to gemini.Adaptor.ConvertClaudeRequest, which performs the correct Claude → (OpenAI →) Gemini conversion.

if a.RequestMode == RequestModeGemini {
    geminiAdaptor := gemini.Adaptor{}
    return geminiAdaptor.ConvertClaudeRequest(c, info, request)
}

Summary by CodeRabbit

Release Notes

• Improvements
  • Enhanced request processing with intelligent adaptive routing capabilities. The adapter now intelligently routes requests to the appropriate handler based on the active model mode configuration. This improvement enhances flexibility and support for multiple model types while preserving backward compatibility with existing request handling behavior.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 1f724622-5e5b-4ae5-b739-1aebede6c1e3

📥 Commits

Reviewing files that changed from the base of the PR and between 9ae9040 and 298e8e4.

📒 Files selected for processing (1)

• relay/channel/vertex/adaptor.go

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Walkthrough

The ConvertClaudeRequest method in the Vertex adaptor now conditionally routes Claude request conversion: if the request mode is Gemini, it delegates to a Gemini adaptor; otherwise, it uses the existing Claude-specific conversion logic.

Changes

Cohort / File(s)	Summary
Vertex Adaptor Conditional Routing relay/channel/vertex/adaptor.go	Added conditional logic to ConvertClaudeRequest that delegates to Gemini adaptor when RequestModeGemini, otherwise preserves existing Claude request handling behavior.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~15 minutes

Possibly related PRs

• fix: kimi claude code #1831: Modifies ConvertClaudeRequest's adaptor instantiation to switch which adaptor type is created/delegated to.
• fix(adaptor): fix reasoning suffix not processing in vertex adapter #2388: Routes Claude-to-Gemini conversion through the Gemini adaptor when RequestModeGemini is set.

Suggested reviewers

• seefs001

Poem

🐰 A clever fork in the road appears,
Where Claude meets Gemini's frontier,
The adaptor now knows which way to go—
Routing requests with a thoughtful flow!
✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main change: adding support for converting Claude-format requests to Gemini format in the Vertex adaptor, which directly addresses the root cause of the bug described in the PR objectives.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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