Add FunctionChoiceBehavior for OpenAI

[milderhc]

Motivation and Context

Description

Fixes #312 #303

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄

[Copilot]

Pull Request Overview

This PR introduces support for a new FunctionChoiceBehavior, which provides an alternative to the existing ToolCallBehavior for invoking functions with OpenAI. Key changes include updating the maximum inflight auto-invokes, enhancing InvocationContext and FunctionInvocation to include a new functionChoiceBehavior field and respective builder methods, and updating sample and service code to leverage the new behavior.

Reviewed Changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
semantickernel-api/src/main/java/com/microsoft/semantickernel/services/TextAIService.java	Increased MAXIMUM_INFLIGHT_AUTO_INVOKES from 5 to 128 to support higher concurrency.
semantickernel-api/src/main/java/com/microsoft/semantickernel/orchestration/InvocationContext.java	Introduced a new functionChoiceBehavior property along with getters and builder support.
semantickernel-api/src/main/java/com/microsoft/semantickernel/orchestration/FunctionInvocation.java	Added a withFunctionChoiceBehavior method and updated invocation chaining to pass the new behavior.
semantickernel-api/src/main/java/com/microsoft/semantickernel/functionchoice/*.java	Added new classes and options to define the behavior for function choice (auto, required, and none).
samples/semantickernel-concepts/...	Updated sample code to use withFunctionChoiceBehavior in place of ToolCallBehavior where applicable.
aiservices/openai/src/main/java/com/microsoft/semantickernel/aiservices/openai/chatcompletion/*.java	Modified OpenAI chat completion logic to integrate the new function choice behavior and updated tool call configuration.
agents/semantickernel-agents-core/src/main/java/com/microsoft/semantickernel/agents/chatcompletion/ChatCompletionAgent.java	Updated the invocation context builder to pass both tool and function choice behaviors.

[Copilot]

Pull Request Overview

This PR introduces support for FunctionChoiceBehavior for OpenAI to improve how function calls are automatically invoked, replacing the previous ToolCallBehavior where appropriate. Key changes include:

• Updating multiple agent and service methods to use FunctionChoiceBehavior with new overloads and chained configuration.
• Refactoring internal logic in OpenAIChatCompletion and ChatCompletionAgent to distinguish auto-invoke behavior for function calls.
• Adjusting sample code and annotations to reflect the new API design.

Reviewed Changes

Copilot reviewed 35 out of 35 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
semantickernel-api/src/main/java/com/microsoft/semantickernel/agents/AgentInvokeOptions.java	Added @nullable annotations and removed extraneous empty lines in the builder.
semantickernel-api/src/main/java/com/microsoft/semantickernel/agents/Agent.java	Added new overloaded invokeAsync methods supporting FunctionChoiceBehavior.
semantickernel-api/src/main/java/com/microsoft/semantickernel/Kernel.java	Minor formatting style change for multi-line method declaration.
samples/semantickernel-concepts/semantickernel-syntax-examples/.../Example59_OpenAIFunctionCalling.java	Updated to use FunctionChoiceBehavior instead of ToolCallBehavior with model ID update.
aiservices/openai/.../OpenAIChatCompletion.java	Extended auto-invoke check by integrating FunctionChoiceBehavior logic and refactored tool call configuration.
agents/semantickernel-agents-core/.../ChatCompletionAgent.java	Refactored internalInvokeAsync to use FunctionChoiceBehavior and support streamlined thread notifications.

Comments suppressed due to low confidence (2)

aiservices/openai/src/main/java/com/microsoft/semantickernel/aiservices/openai/chatcompletion/OpenAIChatCompletion.java:203

• Consider refactoring the nested conditional chain that checks for auto-invoke conditions to improve readability and maintainability.

if (invocationContext != null && invocationContext.getFunctionChoiceBehavior() != null && invocationContext.getFunctionChoiceBehavior() instanceof AutoFunctionChoiceBehavior && ((AutoFunctionChoiceBehavior) invocationContext.getFunctionChoiceBehavior()).isAutoInvoke()) {

samples/semantickernel-concepts/semantickernel-syntax-examples/src/main/java/com/microsoft/semantickernel/samples/syntaxexamples/functions/Example59_OpenAIFunctionCalling.java:42

• [nitpick] Ensure that the updated model ID 'gpt-4o' is supported by the deployment configuration and documented in related release notes.

.getOrDefault("MODEL_ID", "gpt-4o");