fix anthropic streaming tool index increment

[narengogi]

closes #1275

For multiple tool calls, the tool index was not getting updated

[matter-code-review]

Good fix for tool index initialization, but the increment logic could be more explicit and consistent.

[matter-code-review]

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[matter-code-review]

Description

Summary By MatterAI

🔄 What Changed

This pull request addresses an issue where the toolIndex was not correctly updated for multiple tool calls in streaming responses from Anthropic and Google Vertex AI providers. It introduces an initialization of streamState.toolIndex to -1 if it's undefined and simplifies the increment logic to streamState.toolIndex + 1 when a tool_use content block starts.

🔍 Impact of the Change

This ensures accurate and consistent indexing of tool calls during streaming, preventing off-by-one errors and improving the reliability of applications that process multiple tool calls from these streaming APIs.

📁 Total Files Changed

• src/providers/anthropic/chatComplete.ts: Modified AnthropicChatCompleteStreamChunkTransform to correctly initialize and increment streamState.toolIndex.
• src/providers/google-vertex-ai/chatComplete.ts: Modified VertexAnthropicChatCompleteStreamChunkTransform to correctly initialize and increment streamState.toolIndex.

🧪 Test Added

N/A

🔒Security Vulnerabilities

N/A

Motivation

This change is needed to correctly handle the toolIndex in streaming responses from Anthropic and Google Vertex AI, ensuring proper identification and sequencing of tool calls, specifically for multiple tool calls where the index was not getting updated.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)

How Has This Been Tested?

• Unit Tests
• Integration Tests
• Manual Testing

Screenshots (if applicable)

N/A

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Related Issues

closes #1275

Tip

Quality Recommendations

1. Add unit tests to verify the toolIndex increment logic for multiple tool calls in streaming scenarios for both Anthropic and Google Vertex AI transformers.

2. Consider adding a comment explaining the -1 initialization of toolIndex to clarify its purpose in the indexing sequence.

Tanka Poem ♫

Index now counts,
Tools in stream, a clear path.
No more lost numbers,
Science flows, precise and true,
Bug fixed, a small victory. 🔬✨

Sequence Diagram

sequenceDiagram
    participant T as StreamTransformer
    participant RC as ResponseChunk
    participant PC as ParsedChunk
    participant SS as StreamState

    RC->>T: processChunk(responseChunk, streamState)
    Note over T: AnthropicChatCompleteStreamChunkTransform / VertexAnthropicChatCompleteStreamChunkTransform

    alt streamState.toolIndex is undefined
        T->>SS: streamState.toolIndex = -1
    end

    T->>PC: parseChunk(responseChunk)
    Note over T: Check for 'content_block_start' and 'tool_use'

    alt isToolBlockStart (parsedChunk.type === 'content_block_start' && parsedChunk.content_block?.type === 'tool_use')
        T->>SS: streamState.toolIndex = streamState.toolIndex + 1
    end
    T-->>RC: transformedChunk

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