Python: Add InvokeFunctionTool action for declarative workflows

[moonbox3]

Motivation and Context

• Add InvokeFunctionTool action kind that invokes registered Python functions from declarative YAML workflows
• Add WorkflowFactory.register_tool() API for registering sync/async functions by name
• Support expression-based arguments, optional approval flow (requireApproval), and structured output (result + ChatMessage history)
• Add BaseToolExecutor abstract class for future tool types (MCP, API, etc.)
• Add two samples: invoke_function_tool and agent_to_function_tool

Description

• Addresses Python side of .NET Workflows - Add Invoke Functions tool as Object Model Action #2786
• Increases unit test to 88% for the declarative package

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR.

[markwallace-microsoft]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
TOTAL	16515	1997	87%

report-only-changed-files is enabled. No files were changed during this commit :)

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
4216	225 💤	0 ❌	0 🔥	1m 10s ⏱️

[Copilot]

Pull request overview

This PR adds comprehensive support for invoking Python functions as tools in declarative YAML workflows through a new InvokeFunctionTool action. The implementation introduces a well-designed BaseToolExecutor abstract class that provides extensibility for future tool types (MCP, API, etc.) while maintaining consistency with existing workflow patterns.

Changes:

• Added InvokeFunctionTool action executor with support for sync/async functions, expression-based arguments, optional approval flow, and structured output formatting
• Added WorkflowFactory.register_tool() fluent API for registering Python functions by name
• Introduced BaseToolExecutor abstract base class that encapsulates common tool invocation patterns (registry lookup, approval flow, output formatting, error handling)
• Added comprehensive test coverage (88% for declarative package) including tests for function invocation, error handling, approval flow, and factory registration
• Added two sample workflows demonstrating basic function invocation and agent-to-function chaining patterns

Reviewed changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated 17 comments.

Show a summary per file

File	Description
_executors_tools.py	New module with BaseToolExecutor and InvokeFunctionToolExecutor implementations
_factory.py	Added register_tool() method and _tools registry to WorkflowFactory
_declarative_builder.py	Integrated InvokeFunctionToolExecutor into builder with tool registry support
__init__.py	Exported new tool-related classes and constants
test_function_tool_executor.py	Comprehensive test suite for function tool executor (716 lines)
test_workflow_factory.py	Added tests for tool registration and fluent API
test_workflow_handlers.py	Extended tests for various action handlers (695 new lines)
test_workflow_state.py	Added 338 lines of state evaluation tests
test_powerfx_functions.py	Added 443 lines of PowerFx function tests
test_declarative_loader.py	Added 423 lines of loader and factory tests
test_actions_agents.py	New test file (885 lines) for agent action handlers
invoke_function_tool/	Sample workflow demonstrating basic function tool invocation
agent_to_function_tool/	Sample workflow demonstrating agent-to-function tool chaining
README.md	Updated documentation with InvokeFunctionTool action description