refactor: replace AgentConfig class with config_to_agent function

BREAKING CHANGE: Replace class-based AgentConfig with function-based config_to_agent

- Replace AgentConfig class with config_to_agent function for simpler interface
- Remove ToolRegistry dependency - let Agent handle tool loading internally
- Remove DEFAULT_TOOLS concept and raise_exception_on_missing_tool parameter
- Support both file paths and dictionary inputs with file:// prefix handling
- Only pass non-None config values to Agent constructor (use Agent defaults)
- Update experimental module exports to expose config_to_agent function
- Rewrite all tests to use new function-based interface
- Simplify tool handling by delegating to Agent class

New interface:
  from strands.experimental import config_to_agent
  agent = config_to_agent('/path/to/config.json')

Previous interface (removed):
  from strands.experimental.agent_config import AgentConfig
  config = AgentConfig('/path/to/config.json')
  agent = config.to_agent()

🤖 Assisted by Amazon Q Developer

Author: mrlee-amazon

REFACTOR_TODO.md

@@ -0,0 +1,127 @@
+# Agent Config Refactor TODO
+
+## Plan
+Refactor from class-based `AgentConfig` to function-based `config_to_agent` approach:
+
+### Current Interface
+```python
+from strands.experimental.agent_config import AgentConfig
+config = AgentConfig("/path/to/config.json")
+agent = config.to_agent()
+```
+
+### Target Interface
+```python
+from strands.experimental import config_to_agent
+agent = config_to_agent("/path/to/config.json")
+```
+
+## Tasks
+
+### 1. Core Function Implementation
+- [ ] Create `config_to_agent` function in `src/strands/experimental/agent_config.py`
+- [ ] Support both file path and dictionary input
+- [ ] Handle `file://` prefix for file paths
+- [ ] Parse JSON configuration files
+- [ ] Pass configuration directly to Agent constructor
+
+### 2. Tool Handling Simplification
+- [ ] Remove ToolRegistry usage - let Agent handle tools internally
+- [ ] Remove DEFAULT_TOOLS concept
+- [ ] Pass tools list directly from config to Agent
+- [ ] Remove `raise_exception_on_missing_tool` parameter (use Agent's default behavior)
+
+### 3. Configuration Handling
+- [ ] Only pass non-None config values to Agent constructor
+- [ ] Use Agent's default configs when values not specified
+- [ ] Support all Agent constructor parameters from config
+
+### 4. Module Exports
+- [ ] Update `src/strands/experimental/__init__.py` to export `config_to_agent`
+- [ ] Remove `AgentConfig` class export
+
+### 5. Tests Update
+- [ ] Refactor all tests to use `config_to_agent` function
+- [ ] Remove class-based test patterns
+- [ ] Update test imports
+- [ ] Simplify tool-related tests (no more ToolRegistry mocking)
+- [ ] Update file handling tests
+
+### 6. Cleanup
+- [ ] Remove `AgentConfig` class entirely
+- [ ] Remove unused imports and dependencies
+- [ ] Clean up any remaining ToolRegistry references
+
+## Progress Tracking
+- [x] Task 1: Core Function Implementation
+- [x] Task 2: Tool Handling Simplification  
+- [x] Task 3: Configuration Handling
+- [x] Task 4: Module Exports
+- [x] Task 5: Tests Update
+- [x] Task 6: Cleanup
+
+## Completed Work
+
+### ✅ Core Function Implementation
+- Created `config_to_agent` function in `src/strands/experimental/agent_config.py`
+- Supports both file path and dictionary input
+- Handles `file://` prefix for file paths
+- Parses JSON configuration files
+- Passes configuration directly to Agent constructor
+
+### ✅ Tool Handling Simplification
+- Removed ToolRegistry usage - Agent handles tools internally
+- Removed DEFAULT_TOOLS concept
+- Pass tools list directly from config to Agent
+- Removed `raise_exception_on_missing_tool` parameter (uses Agent's default behavior)
+
+### ✅ Configuration Handling
+- Only passes non-None config values to Agent constructor
+- Uses Agent's default configs when values not specified
+- Supports all Agent constructor parameters from config
+
+### ✅ Module Exports
+- Updated `src/strands/experimental/__init__.py` to export `config_to_agent`
+- Removed `AgentConfig` class export
+
+### ✅ Tests Update
+- Refactored all tests to use `config_to_agent` function
+- Removed class-based test patterns
+- Updated test imports
+- Simplified tool-related tests (no more ToolRegistry mocking)
+- Updated file handling tests
+- Fixed model attribute access (`agent.model.config["model_id"]`)
+
+### ✅ Cleanup
+- Removed `AgentConfig` class entirely
+- Removed unused imports and dependencies
+- Cleaned up ToolRegistry references
+
+## Final Interface
+
+### Current Interface (Experimental)
+```python
+from strands.experimental import config_to_agent
+
+agent = config_to_agent("/path/to/amazing-agent.json")
+agent("do the thing")
+```
+
+### Example Configuration
+```json
+{
+  "model": "anthropic.claude-3-5-sonnet-20241022-v2:0",
+  "prompt": "You are a helpful assistant",
+  "tools": ["strands_tools.file_read", "my_app.tools.cake_tool", "/path/to/another_tool.py"],
+  "name": "MyAgent",
+  "agent_id": "agent-123"
+}
+```
+
+## All Tasks Complete! ✅
+
+## Notes
+- Preserve support for both file paths and dictionary inputs
+- Let Agent class handle all tool loading and validation
+- Use Agent's default behavior for missing tools/configs
+- Keep the `file://` prefix functionality

src/strands/experimental/__init__.py

@@ -2,3 +2,7 @@
 
 This module implements experimental features that are subject to change in future revisions without notice.
 """
+
+from .agent_config import config_to_agent
+
+__all__ = ["config_to_agent"]