feat: Add tool contract validation mechanism

[SHINING2024]

Overview

Add a comprehensive tool contract validation system to ensure inputs and outputs conform to defined schemas, improving reliability and catching issues early.

Motivation

• No validation: Currently, tools accept inputs without validation, leading to cryptic errors
• Debug difficulty: Hard to debug issues from invalid inputs/outputs
• Contract enforcement: Schemas are defined but not enforced
• Better error messages: Clear validation errors help users fix issues faster

Technical Implementation

New features in tools/base_tool.py:

• validate_inputs(inputs) - Validates input against input_schema
• validate_outputs(outputs) - Validates output against output_schema
• execute_safe(inputs) - Wraps execute with validation + error handling
• ValidationError - New exception class for validation failures
• Optional jsonschema dependency (graceful fallback if not installed)

Features

✅ Input validation using JSON Schema
✅ Output validation using JSON Schema
✅ Clear, descriptive error messages
✅ Graceful fallback if jsonschema not installed
✅ No breaking changes
✅ Backward compatible

Usage Example

# In your tool subclass, define schemas:
class MyTool(BaseTool):
    input_schema = {
        "type": "object",
        "required": ["input_text"],
        "properties": {
            "input_text": {"type": "string"}
        }
    }
    output_schema = {
        "type": "object",
        "required": ["result"]
    }

# Then use validation:
is_valid, error = tool.validate_inputs({"input_text": "hello"})
result = tool.execute_safe({"input_text": "hello"})

Testing

• ✅ Verify validation works with valid inputs
• ✅ Verify validation catches invalid inputs
• ✅ Test graceful fallback without jsonschema
• ✅ Test execute_safe error handling