[Bugfix] Robust Qwen3 Coder streaming: fragmented tags, speculative decoding fixes, and content tracking

[ExtReMLapin]

Purpose

This PR addresses several reliability issues in the qwen3_coder tool parser during streaming. Similar to the reasoning parser fix, it handles cases where tool call tags are output as raw text fragments rather than special tokens. It also ensures data integrity during high-speed generation (speculative decoding) where multiple parts of a tool call (or content + tool call) arrive in a single delta.

Key Changes

• Fragmented Tag Detection: Switched from delta_text to current_text analysis to reliably detect <tool_call> and other tags even when they are split across multiple small deltas (e.g., < then tool then _call>).
• Content Tracking with _sent_content_idx: Introduced a cursor to track exactly which parts of the stream have been emitted as content. This prevents duplicate content delivery and ensures that raw text tags don't "leak" into the user-visible content before being parsed.
• Combined Content & Tool Calls: Refactored extract_tool_calls_streaming to allow a single DeltaMessage to contain both plain text content and tool call fragments. This is essential when a model transitions from speaking to calling a tool in the middle of a streaming chunk.
• Speculative Decoding Robustness: Fixed a race condition where arguments could be lost if the parameter value and the closing </function> tag arrived in the same delta. The parser now guarantees that all accumulated arguments are emitted before closing the JSON object.
• Inter-tool Call Whitespace: Improved handling of whitespace and transitions between multiple tool calls in a single stream.

Test Plan

• Added test_extract_tool_calls_streaming_split_tag to verify fragmented tag handling.
• Added test_extract_tool_calls_streaming_speculative_decode_loss to verify no data loss during fast generation.
• Added test_extract_tool_calls_streaming_various_chunk_sizes using the exact Qwen 3.6 template to ensure stability across different streaming behaviors.

[claude]

Claude Code Review

This pull request is from a fork — automated review is disabled. A repository maintainer can comment @claude review to run a one-time review.

[gemini-code-assist]

Code Review

This pull request improves the Qwen3CoderToolParser streaming logic by using current_text and a tracking index (_sent_content_idx) to prevent leaking tool call tags into the content stream, supported by a new test case for split tags. Review feedback identifies a missing initialization for current_tool_index which would cause an AttributeError, suggests using find instead of rfind for more reliable tag detection, and notes that the logic for skipping content between tool calls is currently fragile.

[ExtReMLapin]

/gemini review

[gemini-code-assist]

Code Review

This pull request improves the Qwen3 tool parser's handling of streaming tool calls by using current text tracking and partial tag overlap detection to prevent tag fragments from leaking into the content. It also adds a test case for split tags. A review comment identifies a redundant variable initialization in the streaming state reset logic.

[ExtReMLapin]

oh boy I found more bugs with param parsing in streamed mode, fucking hell, MTP is guilty there

[ExtReMLapin]

superseded by #40861