Add FileSystemToolset for file system access

[DEENUU1]

Summary

Add new FileSystemToolset that allows agents to access the local file system with security controls.

Features

• Operations: read, write, list, info, search, delete
• Security controls:
  • allowed_paths - restrict access to specific directories
  • allow_write / allow_delete - control write/delete permissions
  • max_file_size - limit readable file size
  • allowed_extensions - filter by file extensions
• Path traversal protection (prevents ../ attacks)

Usage

from pydantic_ai import Agent
from pydantic_ai.toolsets import FileSystemToolset

agent = Agent(
    'openai:gpt-4.1',
    toolsets=[
        FileSystemToolset(
            allowed_paths=['/home/user/data'],
            allow_write=True,
            allowed_extensions=['.txt', '.json'],
        ),
    ],
)

Also available as FileSystemTool builtin tool configuration:

from pydantic_ai import Agent
from pydantic_ai.builtin_tools import FileSystemTool

agent = Agent(
    'openai:gpt-4.1',
    builtin_tools=[
        FileSystemTool(
            allowed_paths=['/home/user/data'],
        ),
    ],
)

Test plan

• Path validation tests (allowed paths, traversal attacks, cwd restriction)
• Extension filtering tests
• Operation permission tests (read, write, delete)
• File size limit tests
• All file operations (read, write, list, info, search, delete)
• Tool definition generation tests
• Edge cases and error handling
• ToolManager integration test
• 100% coverage for filesystem.py