Fix Qwen3 content extraction breaking code formatting

[iSevenDays]

Summary

Fixes a bug in Qwen3 content extraction where aggressive whitespace cleanup was breaking proper code formatting in non-tool-call streaming output.

Problem

The qwen3::extract_content_during_parsing() function was using an aggressive regex pattern that collapsed multiple newlines:

content = std::regex_replace(content, std::regex(R"(\n\s*\n)"), "\n");

This broke:

• PEP 8 compliance: 2 empty lines between Python functions were collapsed to 1
• Code formatting: Any intentional whitespace structure was lost
• Streaming output: Users requesting properly formatted code received malformed results

Root Cause

The regex R"(\n\s*\n)" replaces any sequence of newline + whitespace + newline with a single newline, which is overly aggressive for content that should preserve formatting.

Solution

✅ Replace aggressive cleanup with gentle trimming

• Remove std::regex_replace(content, std::regex(R"(\n\s*\n)"), "\n")
• Replace with string_strip(content) following original llama.cpp patterns
• Only trim leading/trailing whitespace, preserve internal formatting

✅ Add proper include

• Add #include "../../common/common.h" for string_strip access

✅ Add regression test

• New test_qwen3_whitespace_preservation() validates PEP 8 compliance
• Ensures 2 empty lines between functions are preserved

Testing

• ✅ PEP 8 compliance: 2 empty lines between functions preserved
• ✅ Tool call parsing: All Qwen3 tests continue to pass
• ✅ No regressions: Existing functionality maintained
• ✅ Follows patterns: Matches original llama.cpp whitespace handling

Example

Before (broken):

def celsius_to_fahrenheit(celsius):
    return celsius * 9/5 + 32
def fahrenheit_to_celsius(fahrenheit):  # Missing empty lines\!
    return (fahrenheit - 32) * 5/9

After (fixed):

def celsius_to_fahrenheit(celsius):
    return celsius * 9/5 + 32


def fahrenheit_to_celsius(fahrenheit):  # Proper PEP 8 spacing preserved\!
    return (fahrenheit - 32) * 5/9

Files Changed

• examples/server/parsers/qwen3_parser.hpp - Fix whitespace handling
• tests/test-function-calls.cpp - Add regression test

Test Results

🧹 Testing Qwen3 Whitespace Preservation Fix:
✅ PASS: Qwen3: PEP 8 double empty lines preserved
✅ PASS: Qwen3: Content not empty after processing
✅ PASS: Qwen3: Function content preserved
✅ PASS: Qwen3: Second function preserved