fix: 移除 fcIdx -1 偏移，修复并发工具调用撞键问题

[learner-i]

当 Claude 直接以多个 tool_use 块起始（无文本前导，index=0）时，
-1 偏移导致 index=0 和 index=1 同时映射到 fcIdx=0：

• index=0 的工具 args 先流完，发出一次合法调用 ✓
• index=1 的 args 追加到同一 map 槽位，污染后为非法 JSON，该工具丢失 ✗
• index=2 以后的工具各自独占唯一 fcIdx，正常发出 ✓

结果：每轮并发调用中第 2 个工具必然丢失，
模型收不到对应的工具结果后重试剩余工具，
产生雪球效应（10个→9个→8个...逐轮收缩）。

修复：直接使用 Claude 的 block index 作为 fcIdx，不做偏移。
fcIdx 仅作为本地 map 的 key，只需保证唯一性，无需从 0 开始。

⚠️ 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

(简述：做了什么？为什么这样改能生效？请基于你对代码逻辑的理解来写，避免粘贴未经整理的内容)

🚀 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

(请在此粘贴截图、关键日志或测试报告，以证明变更生效)

修复前（fcIdx -1 偏移，撞键）：
场景 2：并发工具调用（同时写两个文件）
模型: aws.claude-opus-4.6
收到 SSE chunk 共 2 个
其中包含 functionCall 的 chunk: 1 个
✅ functionCall[0]: name=write_file args={'content': 'AAA', 'path': 'a.txt'}
⚠️ 预期 2 个并发调用，实际只收到 1 个

修复后（直接映射，无撞键）：
场景 2：并发工具调用（同时写两个文件）
模型: aws.claude-opus-4.6
收到 SSE chunk 共 3 个
其中包含 functionCall 的 chunk: 2 个
✅ functionCall[0]: name=write_file args={'content': 'AAA', 'path': 'a.txt'}
✅ functionCall[1]: name=write_file args={'content': 'BBB', 'path': 'b.txt'}
✅ 全部通过

复现环境：

• 渠道：Anthropic(14) / AWS Bedrock
• 模型：aws.claude-opus-4.6（该模型倾向于直接 tool_use 起始，无文本前导）
• 请求：Gemini 客户端格式，并发调用 ≥ 2 个工具

验证方法：
发送 streamGenerateContent 请求，要求模型同时调用两次 write_file，
统计收到的 functionCall 数量。
修复前：2 个并发工具调用只收到 1 个（index=1 工具丢失）。
修复后：2 个均正确到达。

Summary by CodeRabbit

• Bug Fixes
  • Fixed tool call indexing in streaming responses to ensure proper index assignment.

[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: a6ce6460-3417-47b1-bf23-d4bacfa1a3cc

📥 Commits

Reviewing files that changed from the base of the PR and between 583da45 and 3682539.

📒 Files selected for processing (1)

• relay/channel/claude/relay-claude.go

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Walkthrough

The PR fixes a tool call index collision bug in Claude streaming responses where concurrent tool calls at index 0 would collide with clamped negative indices, causing arguments to be overwritten in the index map and tool calls to be filtered out.

Changes

Claude Tool Call Index Fix

Layer / File(s)	Summary
Tool call index calculation simplification relay/channel/claude/relay-claude.go	fcIdx now uses claudeResponse.Index directly as a map key instead of subtracting 1 and clamping to 0, eliminating collisions when models respond with tool calls starting at index 0 without text prefix.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Possibly related PRs

• QuantumNous/new-api#3080: Adjusts streaming tool-call state and indexing logic in the same StreamResponseClaude2OpenAI function.
• QuantumNous/new-api#2397: Related fix to Claude streaming tool-call block indexing and emission logic.

Suggested reviewers

• Calcium-Ion

Poem

A rabbit hops through indexes bright,
Where tools collided in the night,
No more the -1 clamp that erred—
Direct the path, the call is heard! 🐰

🚥 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
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	Title is in Chinese and clearly describes the main change: removing the -1 offset for fcIdx to fix concurrent tool call collision issues, which directly aligns with the code change and PR objectives.
Linked Issues check	✅ Passed	Code changes directly address issue #5018 by removing the -1 offset logic and using claudeResponse.Index directly as fcIdx, exactly matching the specified repair objective.
Out of Scope Changes check	✅ Passed	The single change in relay-claude.go (removing -1 offset and clamping logic) is directly scoped to the linked issue; no out-of-scope modifications are present.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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