# Changelog 67: Router Workflow Expansion Engine

**Date:** 2025-12-01
**Type:** Feature
**Task:** TASK-039-13

## Summary

Implemented the Workflow Expansion Engine for the Router Supervisor, providing single-tool to multi-step workflow expansion.

## Changes

### New Files

- `server/router/application/engines/workflow_expansion_engine.py` - Main implementation
- `tests/unit/router/application/test_workflow_expansion_engine.py` - 40 unit tests

### Features

1. **Predefined Workflows**
   - `phone_workflow` - 10 steps for phone/tablet modeling
   - `tower_workflow` - 8 steps for tower/pillar modeling
   - `screen_cutout_workflow` - 4 steps for screen recesses
   - `bevel_all_edges_workflow` - 4 steps for edge beveling

2. **Pattern-Based Expansion**
   - Expands tools to workflows when pattern detected
   - Supports workflow suggestion from `DetectedPattern`

3. **Keyword Matching**
   - Find workflows by keywords (e.g., "phone", "tower")
   - Case-insensitive matching

4. **Parameter Inheritance**
   - `$param_name` syntax to inherit from original call
   - Static params preserved from workflow definition

### API

```python
engine = WorkflowExpansionEngine(config=RouterConfig())
expanded = engine.expand(tool_name, params, context, pattern)
# Returns List[CorrectedToolCall] or None
```

## Related

- Part of Phase 3: Tool Processing Engines
- Implements `IExpansionEngine` interface
