fix: calls to multiple tools in gemini all return index=0

[seefs001]

Maintain the state when converting the gemini tool to openai

Summary by CodeRabbit

• Bug Fixes
  • Improved consistency and stability of tool call handling in Gemini streaming responses.

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[coderabbitai]

Walkthrough

Per-choice tool call indexing is added to Gemini streaming responses. Two maps track stable local indices for tool calls: toolCallIndexByChoice maps choice indices to tool-ID-to-index mappings, and nextToolCallIndexByChoice tracks the next available index per choice. During streaming callbacks, each tool call with a non-empty ID receives a deterministic index via SetIndex.

Changes

Cohort / File(s)	Summary
Gemini Tool Call Indexing relay/channel/gemini/relay-gemini.go	Introduces toolCallIndexByChoice and nextToolCallIndexByChoice maps to assign stable per-choice indices to tool calls in streaming responses. Adds indexing logic during callback processing to ensure deterministic ordering and identification of tool calls for each candidate.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Poem

🐰 In streams of Gemini's cosmic flow,
Tool calls now get indices to show,
Per choice, per ID, stable and true,
Order emerges from chaos—who knew? ✨

🚥 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 directly and clearly describes the specific bug being fixed: tool calls in Gemini responses incorrectly all returning index=0, which matches the summary's solution of adding per-choice indexing.

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✨ Finishing touches

• 📝 Generate docstrings

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