BugFix-Bench

# Agentic Coding Challenge: "The Phantom Content Bug"
## Commit: 2f6267ba7d8fed021415711191307d5efedadc05
## Context
You're working on a proxy service that translates between two API formats (Claude ↔ OpenAI). The service has two execution modes:
- **Enhanced mode**: Runs preprocessing, then main execution  
- **Direct mode**: Skips preprocessing, goes straight to execution

## The Problem
Users report that responses show "(no content)" in their client, but only under specific conditions:
- ✅ Enhanced mode always works perfectly
- ✅ Simple direct requests work fine  
- ❌ Complex direct requests show "(no content)"
- ❌ Issue affects non-"haiku" models more than "haiku" models

## Key Clues
1. Server logs show successful response generation in ALL cases
2. HTTP responses return 200 OK with proper JSON structure
3. The client expects Server-Sent Events (SSE) format
4. Complex requests often involve tool definitions
5. Curl tests work fine, but the specific client application fails

## Your Task
1. **Deep Investigation**: Analyze the codebase to understand why this pattern exists
2. **Root Cause**: Identify the exact mechanism causing content to disappear  
3. **Fix Recommendation**: Propose a specific code solution

## Challenge Elements
- The bug is NOT where the symptoms point (direct vs enhanced flow)
- Multiple code layers are involved in the request pipeline
- The issue lies in a fallback mechanism most developers wouldn't suspect
- Requires tracing through format conversion and streaming logic

## Success Criteria
An effective agent should:
- Resist obvious but wrong conclusions
- Trace through the complete request lifecycle  
- Identify the missing component in response generation
- Provide a concrete code fix with proper event structure

**Difficulty Level**: Intermediate-Advanced (requires systematic code analysis + understanding of SSE streaming protocols)

---

## Testing Instructions for Agents

### Reproduction Steps
1. Make a direct request (no preprocessing) with many tool definitions (>10 tools)
2. Observe that server processes successfully but client shows "(no content)"
3. Compare with enhanced mode requests (with preprocessing) - these work fine
4. Compare with simple direct requests (few/no tools) - these also work fine

### Investigation Areas
- Request routing and mode determination logic
- Tool handling and processing thresholds
- Response format conversion between API formats
- Streaming vs non-streaming response handling
- SSE event structure and content delivery

### Expected Discovery Process
1. **Initial hypothesis**: Direct mode has different response handling
2. **Deeper analysis**: Tool count affects response processing path
3. **Key insight**: Complex requests trigger a fallback mechanism
4. **Root cause**: Fallback creates incomplete event streams
5. **Solution**: Fix the event structure in the fallback path

### Evaluation Criteria
- **Initiative (25%)**: Did the agent proactively analyze code without explicit guidance?
- **Systems Thinking (25%)**: Did they understand the multi-layer architecture?
- **Debugging Methodology (25%)**: Did they follow systematic investigation vs jumping to conclusions?
- **Technical Solution (25%)**: Did they identify the specific missing code and provide a working fix?

## Hint Structure (Progressive Disclosure)

### Level 1 Hint (if agent gets stuck)
> "The issue might not be in the core request processing logic. Look at what happens when the system encounters certain types of complex requests."

### Level 2 Hint (if still struggling)
> "Consider that different request types might trigger different response handling strategies. What happens when the system needs to provide streaming responses but can't?"

### Level 3 Hint (last resort)
> "Focus on forced non-streaming scenarios and how they simulate streaming format for client compatibility."

## Real-World Learning Objectives
This challenge teaches:
- **Code archaeology**: Reading and understanding complex codebases
- **API protocol expertise**: SSE event structure requirements
- **Debugging methodology**: Systematic vs symptomatic analysis
- **Fallback mechanism design**: When primary paths fail, how do backup systems work?
- **Client-server contract debugging**: Understanding format expectations between services

This challenge reflects real-world debugging scenarios where symptoms point in the wrong direction and the actual issue lies in edge case handling or fallback mechanisms.