fix: enable FunctionTool serialization for Temporal worker nodes

[chakrris]

• RunAgent*Params objects must be serializable for over-the-wire transmission to Temporal workers/backend. Previous implementation failed when users specified FunctionTool with callable on_invoke_tool params.
• This commit adds cloudpickle-based serialization support to resolve serialization errors
• During testing, also had to pin OpenAI to v1.99.9 to avoid LiteLLM incompatibility issue (#13711)

[Copilot]

Pull Request Overview

This PR adds cloudpickle-based serialization support for FunctionTool objects to enable Temporal worker node communication. The primary purpose is to resolve serialization errors that occurred when users specified FunctionTool instances with callable on_invoke_tool parameters for over-the-wire transmission to Temporal workers/backend.

Key changes include:

• Refactored FunctionTool class to support automatic serialization/deserialization of callable functions using cloudpickle and base64 encoding
• Added comprehensive test suite covering various callable types (functions, lambdas, closures) and error scenarios
• Pinned OpenAI dependency to version 1.99.9 to resolve LiteLLM compatibility issues

Reviewed Changes

Copilot reviewed 3 out of 6 changed files in this pull request and generated 2 comments.

File	Description
src/agentex/lib/core/temporal/activities/adk/providers/openai_activities.py	Core implementation of FunctionTool serialization with cloudpickle support and property-based callable management
tests/test_function_tool.py	Comprehensive test suite for FunctionTool serialization covering various callable types and error handling scenarios
pyproject.toml	Dependency updates: pinned OpenAI version and added cloudpickle requirement

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[varunursekar]

curious - is there a limit on the size of the payload in temporal? i might be misremembering but i think it might be like 4 mb

[varunursekar]

looks good!

[chakrris]

curious - is there a limit on the size of the payload in temporal? i might be misremembering but i think it might be like 4 mb

I think it's 2 MB: https://dev.agentex.scale.com/docs/concepts/acp/agentic/temporal/?h=size#when-to-use-each-approach