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

contributing/samples/agent_governance/README.md

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+# Agent Governance Toolkit — GovernancePlugin for Google ADK
+
+A governance plugin for [Google ADK](https://github.com/google/adk-python) that enforces
+policy-as-code rules before tool execution, verifies agent identity, and produces
+tamper-evident audit trails.
+
+Built on the [Agent Governance Toolkit](https://github.com/microsoft/agent-governance-toolkit)
+(v3.2.0, 9,500+ tests, MIT licensed).
+
+## Features
+
+- **Policy enforcement** — Evaluate YAML/OPA/Cedar policies before every tool call (<5ms)
+- **Agent identity** — Zero-trust verification via Ed25519 + SPIFFE
+- **Audit logging** — Merkle-chained tamper-evident action logs
+- **Configurable** — Allow/deny/warn/require-approval actions per policy rules
+
+## Install
+
+```bash
+pip install agentmesh-platform[server]
+```
+
+## Usage
+
+```python
+from google.adk.agents import Agent
+from governance_plugin import GovernancePlugin
+
+governance = GovernancePlugin(
+    policy_dir="./policies",
+    agent_did="did:mesh:my-agent",
+)
+
+agent = Agent(
+    name="governed-agent",
+    model="gemini-2.0-flash",
+    tools=[my_tool],
+    plugins=[governance],
+)
+```
+
+## Policy Example (policies/default.yaml)
+
+```yaml
+apiVersion: governance.toolkit/v1
+name: adk-agent-policy
+rules:
+  - name: block-dangerous-tools
+    condition: "action in ['shell_exec', 'file_delete']"
+    action: deny
+  - name: rate-limit-api-calls
+    condition: "action == 'api_call'"
+    action: allow
+    limit: "100/hour"
+```
+
+## How It Works
+
+The plugin hooks into ADK's `before_tool_call` lifecycle:
+
+1. **Before tool execution** — GovernancePlugin evaluates the tool name + arguments against loaded policies
+2. **Identity check** — Optionally verifies the calling agent's DID
+3. **Decision** — Allow, deny, warn, or require approval
+4. **Audit** — Logs the decision with Merkle hash chaining
+
+## Links
+
+- [Agent Governance Toolkit](https://github.com/microsoft/agent-governance-toolkit)
+- [Policy-as-Code Tutorial](https://github.com/microsoft/agent-governance-toolkit/tree/main/docs/tutorials/policy-as-code)
+- [OWASP Agentic Compliance](https://github.com/microsoft/agent-governance-toolkit/blob/main/docs/OWASP-COMPLIANCE.md)

contributing/samples/agent_governance/governance_plugin.py

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+# Copyright 2026 Microsoft Corporation
+#
+# Licensed under the MIT License.
+"""
+GovernancePlugin for Google ADK.
+
+Enforces policy-as-code rules before tool execution, verifies agent
+identity, and produces tamper-evident audit trails using the Agent
+Governance Toolkit (https://github.com/microsoft/agent-governance-toolkit).
+"""
+
+from __future__ import annotations
+
+import logging
+from pathlib import Path
+from typing import Any
+
+logger = logging.getLogger(__name__)
+
+
+class GovernancePlugin:
+    """ADK plugin that enforces governance policies before tool execution.
+
+    Usage::
+
+        from governance_plugin import GovernancePlugin
+
+        governance = GovernancePlugin(policy_dir="./policies")
+        agent = Agent(name="my-agent", plugins=[governance])
+    """
+
+    def __init__(
+        self,
+        policy_dir: str | Path = "./policies",
+        agent_did: str = "did:mesh:adk-agent",
+        sponsor_email: str = "adk-operator@example.com",
+        default_action: str = "allow",
+    ) -> None:
+        self._policy_dir = Path(policy_dir)
+        self._agent_did = agent_did
+        self._sponsor_email = sponsor_email
+        self._default_action = default_action
+        self._engine = None
+        self._audit = None
+        self._setup()
+
+    def _setup(self) -> None:
+        """Initialize AGT policy engine and audit service."""
+        try:
+            from agentmesh.governance.policy import PolicyEngine
+            from agentmesh.services.audit import AuditService
+
+            self._engine = PolicyEngine()
+            self._audit = AuditService()
+
+            if self._policy_dir.exists():
+                for f in sorted(self._policy_dir.glob("*.yaml")):
+                    try:
+                        self._engine.load_yaml(f.read_text())
+                        logger.info("Loaded policy: %s", f.name)
+                    except Exception as exc:
+                        logger.warning("Skipped %s: %s", f.name, exc)
+
+            logger.info(
+                "GovernancePlugin initialized (agent=%s, policies=%s)",
+                self._agent_did,
+                self._policy_dir,
+            )
+        except ImportError:
+            logger.warning(
+                "agentmesh-platform not installed. "
+                "Install with: pip install agentmesh-platform"
+            )
+
+    def before_tool_call(
+        self,
+        tool_name: str,
+        args: dict[str, Any] | None = None,
+        **kwargs: Any,
+    ) -> dict[str, Any]:
+        """Evaluate governance policy before a tool call.
+
+        Returns:
+            Dict with 'allowed' (bool), 'decision', 'reason', and
+            'audit_entry_id'.
+        """
+        if self._engine is None:
+            return {"allowed": True, "decision": "allow", "reason": "AGT not installed"}
+
+        context = {
+            "action": tool_name,
+            "tool_args": args or {},
+            **kwargs,
+        }
+
+        result = self._engine.evaluate(
+            agent_did=self._agent_did,
+            context=context,
+        )
+
+        if self._audit:
+            entry = self._audit.log_policy_decision(
+                agent_did=self._agent_did,
+                action=tool_name,
+                decision=result.action,
+                policy_name=result.policy_name or "",
+                data={"tool_args": args or {}, "reason": result.reason},
+            )
+            audit_id = entry.entry_id
+        else:
+            audit_id = None
+
+        return {
+            "allowed": result.allowed,
+            "decision": result.action,
+            "reason": result.reason,
+            "matched_rule": result.matched_rule,
+            "audit_entry_id": audit_id,
+        }
+
+    def get_audit_summary(self) -> dict[str, Any]:
+        """Return audit service summary."""
+        if self._audit:
+            return self._audit.summary()
+        return {"error": "Audit service not initialized"}

contributing/samples/agent_governance/main.py

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+# Copyright 2026 Microsoft Corporation
+#
+# Licensed under the MIT License.
+"""
+Example: Google ADK agent with Agent Governance Toolkit policy enforcement.
+
+Demonstrates:
+1. Loading YAML governance policies
+2. Evaluating policies before tool calls
+3. Producing tamper-evident audit trails
+"""
+
+from pathlib import Path
+
+from google.adk.agents import Agent
+from governance_plugin import GovernancePlugin
+
+
+def create_governed_agent() -> Agent:
+    """Create an ADK agent with governance controls."""
+    governance = GovernancePlugin(
+        policy_dir=Path(__file__).parent / "policies",
+        agent_did="did:mesh:adk-demo-agent",
+    )
+
+    # Example: check policy before a tool call
+    result = governance.before_tool_call(
+        tool_name="web_search",
+        args={"query": "latest AI safety research"},
+    )
+    print(f"Policy decision: {result['decision']} — {result['reason']}")
+
+    # Check audit trail
+    summary = governance.get_audit_summary()
+    print(f"Audit: {summary['total_entries']} entries, chain valid: {summary['chain_valid']}")
+
+    return Agent(
+        name="governed-research-agent",
+        model="gemini-2.0-flash",
+        instruction="You are a research assistant with governance controls.",
+    )
+
+
+if __name__ == "__main__":
+    agent = create_governed_agent()
+    print(f"Agent '{agent.name}' created with governance enabled.")

contributing/samples/agent_governance/policies/default.yaml

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+apiVersion: governance.toolkit/v1
+name: adk-demo-policy
+description: Example governance policy for Google ADK agents
+rules:
+  - name: block-shell-execution
+    condition: "action in ['shell_exec', 'code_exec', 'file_delete']"
+    action: deny
+    description: Block dangerous system-level tool calls
+    priority: 100
+
+  - name: rate-limit-api-calls
+    condition: "action == 'api_call'"
+    action: allow
+    limit: "100/hour"
+    description: Rate limit external API calls
+    priority: 50
+
+  - name: require-approval-for-payments
+    condition: "action == 'process_payment'"
+    action: require_approval
+    approvers: ["admin@example.com"]
+    description: Payment actions require human approval
+    priority: 90
+
+default_action: allow