fix: Claude stream block index/type transitions

[seefs001]

fix #2695
claude的vscode插件会依赖返回信息的index，在交错思考情况下不符合插件预期。
attach文件再请求即可复现，终端使用不受影响。
另外VsCode插件上传文件没有被读取到，原因为OpenAI转Claude没有兼容文件类型，在另外的PR(#2689
)中有处理。

tips：不建议在有条件用claude原生格式的情况下使用转换，并非所有模型都有同样的交错思考的概念，未必能完美兼容，对性能也或许有一定的损耗。

[coderabbitai]

Walkthrough

Two files are modified to improve tool-call indexing in Claude-to-OpenAI streaming conversion. New fields are added to the ClaudeConvertInfo struct to track tool-call indices, while service/convert.go implements helper functions and logic to properly manage content block state transitions and index propagation during tool-call streaming.

Changes

Cohort / File(s)	Summary
Struct State Tracking relay/common/relay_info.go	Added two integer fields (ToolCallBaseIndex, ToolCallMaxIndexOffset) to ClaudeConvertInfo struct for tracking tool-call indexing state.
Streaming Conversion Logic service/convert.go	Introduced stopOpenBlocks and stopOpenBlocksAndAdvance helpers to manage content block termination across text/thinking/tools transitions. Added tool-call tracking state initialization, replaced direct Index references with local variables for precise block positioning, and updated tool_call handling to compute and propagate correct block indices for nested tool_use blocks with corresponding content_block events.

Sequence Diagram

sequenceDiagram
    participant Stream as Streaming Handler
    participant State as ClaudeConvertInfo State
    participant Blocks as Content Block Manager
    participant Events as Event Emitter

    Stream->>State: Detect tool_call in stream
    Stream->>State: Initialize ToolCallBaseIndex & ToolCallMaxIndexOffset
    
    alt Open Block Exists
        Stream->>Blocks: stopOpenBlocks()
        Blocks->>Events: Emit content_block_stop (previous block)
    end
    
    Stream->>Blocks: Compute correct block index
    Blocks->>Events: Emit content_block_start (tool_use)
    
    loop For Each Tool Call Delta
        Stream->>Blocks: Emit content_block_delta with correct Index
        Blocks->>Events: Stream delta event
    end
    
    Stream->>Blocks: Finalize block state
    Blocks->>Events: Emit content_block_stop (tool_use)
    Events->>Events: Report usage + finish_reason

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~30 minutes

Possibly related PRs

• fix: try to fix tool call issues #2397: Modifies Claude-to-OpenRouter streaming conversion for tool-call and content_block event emission sequencing, directly related to content_block indexing changes.
• feat: 完善格式转换，修复gemini渠道和openai渠道在claude code中使用的问题 #1531: Enhances Claude-to-OpenAI stream conversion with improved tool-call tracking and handling, addressing similar content_block management concerns.

Poem

🐰 Hippity-hop through blocks we go,
Tool calls dancing to and fro,
Index tracking, state so true,
Content blocks in perfect queue! 🎯

🚥 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 accurately describes the main purpose of the changes: fixing how Claude handles stream block indices and type transitions during tool call processing.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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