feat: genkit agents

[xavidop]

Description

Support For Genkit Agents

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Code refactoring
• Performance improvement
• Test improvements
• CI/CD improvements

Changes Made

Testing

• Unit tests added/updated
• Integration tests added/updated
• Manual testing performed
• All existing tests pass

Checklist

• My code follows the project's code style guidelines
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published

Breaking Changes

New agents redefined

Documentation

• README updated
• Plugin documentation updated
• API documentation updated
• Sample code updated

[gemini-code-assist]

Code Review

This pull request introduces the beta Agents API for Genkit Java, replacing the old agent and chat session implementations with a robust stateful, multi-turn agent framework. It adds the com.google.genkit.ai.agent package, supporting both server-managed and client-managed sessions, bidirectional streaming, detached execution, and session state persistence. Feedback on these changes highlights critical security vulnerabilities regarding path traversal in FileSessionStore where sessionId is resolved against the filesystem without validation. Additionally, a potential ClassCastException was identified in InProcessTransport due to raw class deserialization of parameterized state, a redundant filter was found in FileSessionStore's chain pruning, and a potential thread leak was noted due to an unclosed ScheduledExecutorService.

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[gemini-code-assist]

Because AgentOutput.class is a raw class, Jackson will deserialize the parameterized custom state field as a LinkedHashMap instead of the concrete POJO class S. This will cause a ClassCastException when the caller attempts to cast or use the state as S. To support custom POJO state types correctly, the Agent and transport should be aware of the concrete Class<S> stateType (which can be passed from CustomAgentConfig) and use Jackson's TypeFactory to construct the proper parametric type (e.g., mapper.getTypeFactory().constructParametricType(AgentOutput.class, stateType)).