fix: preserve Claude tool block indexes

[lxil520]

⚠️ 提交说明 / PR Notice

Important

• 请提供人工撰写的简洁摘要，避免直接粘贴未经整理的 AI 输出。

📝 变更描述 / Description

Anthropic content block indexes identify which stream block a tool_use or input_json_delta belongs to. The OpenAI-compatible stream response previously subtracted one and clamped to zero, so Claude tool blocks with indexes 0 and 1 could both be emitted as OpenAI tool call index 0. This keeps Claude's original block index when emitting tool calls and adds a regression test for two sequential tool blocks.

🚀 变更类型 / Type of change

• 🐛 Bug 修复 (Bug fix) - 请关联对应 Issue，避免将设计取舍、理解偏差或预期不一致直接归类为 bug
• ✨ 新功能 (New feature) - 重大特性建议先通过 Issue 沟通
• ⚡ 性能优化 / 重构 (Refactor)
• 📝 文档更新 (Documentation)

🔗 关联任务 / Related Issue

• Closes Bug: StreamResponseClaude2OpenAI fcIdx 撞键导致并发工具调用丢失 #5018

✅ 提交前检查项 / Checklist

• 人工确认: 我已亲自整理并撰写此描述，没有直接粘贴未经处理的 AI 输出。
• 非重复提交: 我已搜索现有的 Issues 与 PRs，确认不是重复提交。
• Bug fix 说明: 若此 PR 标记为 Bug fix，我已提交或关联对应 Issue，且不会将设计取舍、预期不一致或理解偏差直接归类为 bug。
• 变更理解: 我已理解这些更改的工作原理及可能影响。
• 范围聚焦: 本 PR 未包含任何与当前任务无关的代码改动。
• 本地验证: 已在本地运行并通过测试或手动验证，维护者可以据此复核结果。
• 安全合规: 代码中无敏感凭据，且符合项目代码规范。

📸 运行证明 / Proof of Work

GOCACHE=/private/tmp/new-api-go-cache GOMODCACHE=/private/tmp/new-api-go-mod go test ./relay/channel/claude -run 'TestStreamResponseClaude2OpenAIUsesClaudeBlockIndexForToolCalls' -count=1

Result:

ok   github.com/QuantumNous/new-api/relay/channel/claude   0.820s

[coderabbitai]

Walkthrough

The PR fixes an off-by-one index calculation bug in Claude-to-OpenAI streaming response translation. The fcIdx value now uses Claude's content-block index directly instead of subtracting 1 and clamping to 0, eliminating index collisions that corrupted concurrent tool-call arguments.

Changes

Claude tool call indexing fix

Layer / File(s)	Summary
Tool index calculation and validation relay/channel/claude/relay-claude.go, relay/channel/claude/relay_claude_test.go	The fcIdx calculation in StreamResponseClaude2OpenAI now uses claudeResponse.Index directly, removing the previous -1 offset. A new test validates that tool-call indices are preserved from Claude's content_block_start index values without collisions.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• QuantumNous/new-api#2854: Both PRs adjust Claude→OpenAI streaming tool-call Index mapping to derive tool call ordering directly from Claude content-block indices (including new base/max index tracking and corrected transition/index handling), so the main PR's fcIdx change is part of the same tool-call indexing behavior.
• QuantumNous/new-api#3080: Both PRs modify StreamResponseClaude2OpenAI's tool-call Index mapping logic in relay/channel/claude/relay-claude.go to derive the OpenAI-style tool call ordering from Claude content_block_start indices (including the exact off-by-one/index selection).

Suggested reviewers

• seefs001
• Calcium-Ion

Poem

🐰 A bunny hops through tool calls true,
No more collisions blocking through!
Index by index, clear and bright,
Concurrent tools now work just right! 🎉

🚥 Pre-merge checks | ✅ 4 | ❌ 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 (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'fix: preserve Claude tool block indexes' directly relates to the main change—removing the -1 offset to preserve Claude's block index as fcIdx.
Linked Issues check	✅ Passed	The code changes directly address issue #5018: removing the -1 offset and clamping logic from fcIdx computation, and adding a test verifying the new behavior.
Out of Scope Changes check	✅ Passed	All changes are scoped to the reported issue: fcIdx fix in relay-claude.go and corresponding test in relay_claude_test.go.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[seefs001]

issue创建者提交的PR已经合并 #5095