feat: add Agent Governance Toolkit sample — policy enforcement for ADK agents

[imran-siddique]

Summary

Adds a community sample demonstrating the Agent Governance Toolkit (AGT) integration with Google ADK, as discussed in google/adk-python#5418 and invited by @DeanChensj.

What's included

File	Description
\governance_plugin.py\	GovernancePlugin — evaluates YAML/OPA/Cedar policies before tool calls, logs to Merkle audit chain
\main.py\	Example usage with an ADK agent
\policies/default.yaml\	Sample policy (block shell exec, rate limit APIs, require approval for payments)
\README.md\	Documentation with install, usage, and policy examples

How it works

\
Tool call → GovernancePlugin.before_tool_call() → Policy evaluation (<5ms) → Allow/Deny/Warn → Audit log
\\

Requirements

\\�ash
pip install google-adk agentmesh-platform
\\

AGT Stats

• v3.2.0 Public Preview, 9,500+ tests, MIT licensed
• 5 SDK languages, 12+ framework integrations
• 10/10 OWASP Agentic Top 10 coverage

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[DeanChensj]

We can have a plugins/ folder under src/google/adk_community to host the plugin

[DeanChensj]

Why Microsoft?