fix(rust): make ChatCompletionChunk a transparent Value passthrough

[AnthonyRonning]

Problem

Streaming chat completions with multiple tool calls fail with:

Failed to parse chunk: invalid type: null, expected a string at line 1 column 230

The OpenAI streaming spec sends null for id, type, and function.name in subsequent tool_call delta chunks after the first. The SDK's ToolCall struct had these as required String fields, causing deserialization failures.

Fix

Replace the typed streaming structs (ChatCompletionChunk, ChatChoiceDelta, ChatMessageDelta) with a single transparent serde_json::Value wrapper:

#[derive(Debug, Clone, Serialize, Deserialize)]
#[serde(transparent)]
pub struct ChatCompletionChunk(pub Value);

This makes the streaming path a full JSON passthrough -- any valid JSON from the backend flows through without the SDK ever failing on null, absent, or new fields.

Also

• Fixes kimi-k2-thinking -> kimi-k2-5 model name in tests (old model no longer available)
• Adds test_streaming_multi_tool_calls integration test that verifies parallel tool call streaming works end-to-end

Testing

Verified against the dev instance (enclave.secretgpt.ai) with glm-5 model via maple-proxy:

• Non-streaming tool calls: pass
• Streaming single tool call: pass
• Streaming multi-tool calls (previously broken): pass
• All existing SDK unit tests: pass

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Summary by CodeRabbit

• New Features

  • Function and Tool types are now publicly available and can be imported directly.
  • Streaming responses with multiple tool calls are now supported.

• Refactor

  • Streaming response structure has been updated to a unified wrapper format.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

---

📝 Walkthrough

Walkthrough

The pull request replaces three fixed streaming delta types (ChatCompletionChunk, ChatChoiceDelta, ChatMessageDelta) with a single transparent wrapper ChatCompletionChunk that encapsulates a generic Value. This enables passthrough of raw backend JSON without deserialization constraints. Tests are updated to access chunk data via JSON navigation rather than structured field access, and a new streaming test for multiple tool calls is added.

Changes

Cohort / File(s)	Summary
Type Definitions rust/src/types.rs	Removed three structured streaming delta types; added transparent ChatCompletionChunk(pub Value) wrapper to allow direct JSON passthrough and accommodate evolving backend fields.
Integration Tests rust/tests/ai_integration.rs	Updated imports to export Function and Tool; refactored chunk field access throughout tests from structured paths (e.g., chunk.choices[0].delta.content) to JSON value paths (e.g., chunk.0["choices"][0]["delta"]["content"]); added new test_streaming_multi_tool_calls test for verifying multiple tool calls in streaming responses.
API Integration Tests rust/tests/api_keys.rs	Updated streaming response parsing to extract content via JSON value traversal (chunk.0["choices"].as_array()...["delta"]["content"]) instead of structured field access.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• feat: make ChatMessage content field flexible to support multiple for… #47: Modifies streaming chat types to use serde_json::Value for delta/content passthrough, achieving similar compatibility goal through different mechanism.
• feat: add tool calling types to Rust SDK #53: Directly overlaps by modifying ChatMessageDelta and related delta structs; this PR removes them while the related PR adds tool-calling fields to them.
• feat(rust): add reasoning_content field to ChatMessage types #62: Directly modifies streaming message types in rust/src/types.rs; this PR removes ChatMessageDelta while the related PR adds reasoning_content field to it.

Poem

🐰 Whiskers twitching with delight,
Types shed their rigid chains so tight,
A transparent wrapper born to be free,
JSON streams through—wild and carefree!
No more fretting over unknown fields,
Our schema's heart forever yields! ✨

🚥 Pre-merge checks | ✅ 2

✅ 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 clearly and specifically describes the main change: converting ChatCompletionChunk to a transparent Value wrapper for JSON passthrough.

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✨ Finishing Touches

• 📝 Generate docstrings (stacked PR)
• 📝 Generate docstrings (commit on current branch)

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/streaming-tool-call-passthrough

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 4 additional findings.