[Feature Request]: Add framework-neutral agent-hooks contract to govern ADK agents #6602

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🔴 Required Information

Is your feature request related to a specific problem?

ADK exposes rich lifecycle seams through BasePlugin, but there is no
standard, framework-neutral way to plug governance and policy enforcement
(policy engines, content filters, PII redaction, egress guards, rate
limiters) into those seams. Today each team hand-writes bespoke callback
logic per agent. That is inconsistent, easy to accidentally "fail open,"
hard to audit, and not portable across agent frameworks. There is no
uniform allow / deny / transform decision contract, no fail-closed
guarantee, and no built-in, auditable record of why an action was
allowed, blocked, or rewritten.

Describe the Solution You'd Like

Add AgentHooksPlugin: a BasePlugin that makes ADK a conformant host
for agent-hooks, a
framework-neutral control contract. You register one or more interceptors
once, and every governed ADK lifecycle point delegates its decision to the
agent-hooks emitter, which runs the interceptors, returns a Verdict
(allow / deny / transform), and records each decision as an auditable
InterceptionRecord.

API changes (all additive):

• New public export google.adk.plugins.AgentHooksPlugin.
• New optional extra: pip install "google-adk[agent-hooks]" (backed by
  agent-hooks-sdk, a compiled-core optional dependency). The import is
  deferred to plugin construction, so importing google.adk.plugins never
  requires it.
• Interceptor contract: any object with intercept(AgentContext) -> Verdict
  (sync or async). No ADK-specific base class required — the same
  interceptor runs on other agent-hooks hosts (crewAI, ...).

Enforcement is fail-closed: deny blocks the guarded action,
transform rewrites the guarded value at $target, and any engine error,
malformed verdict, or interceptor timeout becomes a fail-closed deny — it
never fails open. mode="evaluate_only" records verdicts without acting.

Impact on your work

This gives us one consistent, auditable governance layer across ADK agents
instead of per-agent callback code, and lets teams
enforce the same interceptor across ADK and other frameworks. It is
foundational for governed/regulated deployments where every tool call,
model call, input, and output must be policy-checked and logged.

Willingness to contribute

Yes.

🟡 Recommended Information

Describe Alternatives You've Considered

• Framework-specific middleware. Locks policy to one framework;
  agent-hooks is framework-neutral, so the same interceptor is portable.
• Hand-written BasePlugin callbacks per project. Works, but is
  reimplemented everywhere, has no shared verdict model or audit trail, and
  is easy to accidentally fail open.
• Provider/model-side guardrails only. They don't uniformly cover tool
  calls, tool results, user input, final output, and run lifecycle.

Proposed API / Implementation

from google.adk.apps.app import App
from google.adk.plugins import AgentHooksPlugin
from agent_hooks import AgentContext, Decision, Verdict

class ToolGovernance:
    name = "tool_governance"

    def intercept(self, ctx: AgentContext) -> Verdict:
        if ctx["interception_point"] == "pre_tool_call":
            if ctx["tool_call"]["name"] == "delete_account":
                return Verdict.deny(reason="tool_denied",
                                    message="disabled by policy")
        return Verdict(decision=Decision.ALLOW)

records = []
plugin = AgentHooksPlugin(
    interceptors=[ToolGovernance()],
    mode="enforce",              # or "evaluate_only" to observe without acting
    record_sink=records.append,  # one auditable InterceptionRecord per decision
)
app = App(name="demo", root_agent=root_agent, plugins=[plugin])

Constructor (defaults shown): AgentHooksPlugin(interceptors, name="agent_hooks", mode="enforce", timeout=5.0, composition=None, identity_provider="jcs-sha256", record_sink=None, max_records=1000).

Additional Context

Interception-point mapping (ADK callback → agent-hooks point):

Notes:

• pre_model_call supports allow/deny only; a transform there is
  treated as a fail-closed deny, because rebuilding a provider-native
  request from wire messages is not round-trip safe.
• Trust model: agent-hooks is a cooperative control contract, not
  a security boundary. Interceptors run in-process with full data access and
  the interception points do not guarantee complete mediation.