fix: include closing brace in tool call arguments substring extraction

[AshtonVaughan]

Bug

std::string::substr(pos, count) takes length as the second argument, not end position. The current extraction in 7 places drops the closing brace:

size_t brace_start = json_str.find("{", args_pos);
size_t brace_end = json_str.rfind("}");
if (brace_start != std::string::npos && brace_end != std::string::npos && brace_end > brace_start) {
    arguments = json_str.substr(brace_start, brace_end - brace_start);
}

For input "arguments": {"limit": 6} where brace_start=13 and brace_end=23, this returns 10 characters starting at index 13, which gives {"limit": 6 instead of {"limit": 6}. The closing brace at position 23 is excluded.

Fix

Add + 1 to the length argument so the closing brace is included.

Affected files

7 occurrences across 5 model parsers:

• src/common/AutoModel/modeling_qwen2.cpp:136
• src/common/AutoModel/modeling_qwen3.cpp:151
• src/common/AutoModel/modeling_qwen3.cpp:296
• src/common/AutoModel/modeling_qwen3.cpp:500
• src/common/AutoModel/modeling_qwen3vl.cpp:248
• src/common/AutoModel/modeling_qwen3_5vl.cpp:258
• src/common/AutoModel/modeling_nanbeige.cpp:298

Verification

C++ standard says substr(pos, count) returns a substring of length up to count starting at position pos. Last character is at pos + count - 1, so the original code excludes the character at brace_end. After the fix, last character is at brace_end, which is the closing brace.

The streaming parsers (parse_stream_content) use nlohmann::json::parse and were not affected by this bug. Only the non-streaming substring path was missing the closing brace.

Possible related issue

This may explain part of #483 (tool call arguments serialization). When the closing brace is missing, downstream JSON parsers either fail or attempt error recovery, which could plausibly produce the int-as-string behaviour reported there. Recommend testing against #483's reproduction after this fix lands.

[Copilot]

Pull request overview

This PR aims to fix non-stream tool-call argument extraction by adjusting std::string::substr(pos, count) length calculations so the closing brace is included.

Changes:

• Update 7 tool-call argument substring extractions to use brace_end - brace_start + 1.
• Apply the same fix across Qwen2, Qwen3 (and variants), Qwen3VL, Qwen3.5VL, and Nanbeige non-stream parsers.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
src/common/AutoModel/modeling_qwen3vl.cpp	Adjusts non-stream tool-call arguments substring length.
src/common/AutoModel/modeling_qwen3_5vl.cpp	Adjusts non-stream tool-call arguments substring length.
src/common/AutoModel/modeling_qwen3.cpp	Adjusts non-stream tool-call arguments substring length in 3 parsers.
src/common/AutoModel/modeling_qwen2.cpp	Adjusts non-stream tool-call arguments substring length.
src/common/AutoModel/modeling_nanbeige.cpp	Adjusts non-stream tool-call arguments substring length.

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