Using Copilokit Frontend tools with Orchestrator-style ADK agents

When building an **orchestrator-style ADK agent** (an agent that delegates work to other ADK agents), there is currently **no clear or supported way** to use **Frontend tools** (exposed via `useFrontendTool` in CopilotKit) within that orchestration flow.

This makes it difficult to combine:

* **Orchestrator agents** (routing / delegation)
* **ADK agents**
* **Frontend-only tools**

in a single, clean architecture.

***

## **Background**

From the documentation and examples, there are two common patterns:

1. **ADK agents with tools**
* Tools are attached on the backend (e.g., `MCPToolset`)
* Works well with orchestrators

2. **Frontend tools**
* Tools registered via `useFrontendTool`
* Used by CopilotKit at runtime
* Backend ADK agents connected to Orchestrator ADK agent are **not aware** of these tools

Both patterns work individually, but they **don’t compose well together**.

***

## **Current Behavior**

* An individual ADK agent can use Frontend tools when they are registered via `useFrontendTool`.
* However, when using an **orchestrator-style ADK agent** that delegates to other ADK agents:
* The orchestrator can call child agents
* But those child agents **cannot access Frontend tools**
* Because Frontend tools only exist in the CopilotKit runtime, not in the ADK agent graph

**As a result:**

Orchestrator → ADK agent → Frontend tools

is **not possible**.

***

## **Expected / Desired Behavior**

It would be helpful to have a supported way to achieve one of the following:

### **Option A – Delegation-Friendly Frontend Tools**

Provide a mechanism where:

* An orchestrator delegates to another ADK agent
* That agent can still invoke Frontend tools
* Even though the tools are registered in the frontend runtime

### **Option B – Clear Guidance / Recommended Pattern**

If this is intentionally unsupported, clear documentation explaining:

* Why frontend tools cannot be used with agents in orchestrators
* What the recommended alternative architecture is

***

## **Why This Matters**

Frontend MCP tools are useful or required when:

* MCP servers are browser-only
* Authentication or context must live in the browser
* Tools are tightly coupled to UI/runtime state

At the same time, orchestrator agents are a core pattern for:

* Routing requests
* Multi-agent reasoning
* Structured task delegation

**Right now, developers must choose one or the other.**

***

## **Minimal Conceptual Example**

* **Orchestrator ADK agent**
* Delegates tasks to other ADK agents
* Those ADK agents rely on MCP tools
* MCP tools are frontend-only (registered via `useFrontendTool`)

**Result:**

* Direct usage works
* Orchestrated usage does not

***

## **Example Scenario**

Consider the following setup:

* An **orchestrator-style ADK agent**
* Responsible only for routing and delegation
* Multiple ADK agents
* Each agent has its own instructions and behavior
* A single MCP server
* Exposed as a Frontend MCP
* Tools are registered using `useFrontendTool` in CopilotKit
* Tools are only available at runtime in the frontend

**Conceptually:**

User
↓
Orchestrator ADK Agent
↓
ADK Agent A / ADK Agent B
↓
Frontend MCP Tools (via CopilotKit)

### **What works**

* When an individual ADK agent is used directly:
* Frontend MCP tools are registered via `useFrontendTool`
* The model can successfully call MCP tools

### **What does not work**

* When the orchestrator ADK agent is used:
* The orchestrator delegates to another ADK agent
* That ADK agent cannot access Frontend MCP tools
* Because the tools only exist in the CopilotKit runtime and are not visible to the orchestrator flow

**As a result:**
The same ADK agent behaves differently depending on whether it is called directly or via an orchestrator.

***

## **Closing**

This is not necessarily a bug, but a **missing integration point** that becomes apparent when building real-world, multi-agent applications that mix ADK orchestration with frontend MCP tooling.

Any guidance or recommended patterns would be greatly appreciated.

**Thanks!**