feat(tools): Add AgentDispatcherToolset for runtime agents

contributing/samples/tools/agent_dispatcher/README.md

@@ -0,0 +1,23 @@
+# Agent Dispatcher Sample
+
+Demonstrates [`AgentDispatcherToolset`](../../../../src/google/adk/tools/agent_dispatcher/_agent_dispatcher_toolset.py) for [issue #4759](https://github.com/google/adk-python/issues/4759).
+
+## Capabilities
+
+- **Background dispatch** (default): orchestrator continues while specialists run
+- **Parallel multi-dispatch**: multiple `dispatch_agent` calls in one turn
+- **`await_agent` / `get_agent_result`**: poll or wait for completion
+- **`message_agent`**: follow-ups on the same persistent child session
+- **Allowlisted tools + skills** via toolset constructor
+- **Shared session service**: child sessions use the parent session service by default
+
+## Run
+
+```bash
+adk run contributing/samples/tools/agent_dispatcher
+```
+
+Try:
+
+- "Dispatch two researchers in parallel on ADK and Gemini, then await both."
+- "Research ADK, then ask the same specialist a follow-up."

contributing/samples/tools/agent_dispatcher/__init__.py

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+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from . import agent

contributing/samples/tools/agent_dispatcher/agent.py

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+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Sample orchestrator that dispatches runtime agents with follow-ups.
+
+Demonstrates AgentDispatcherToolset for issue #4759: spawn an arbitrary
+child agent mid-run, then message it again on the same persistent session.
+"""
+
+from __future__ import annotations
+
+from google.adk import Agent
+from google.adk.tools.agent_dispatcher import AgentDispatcherToolset
+
+
+def lookup_fact(topic: str) -> dict[str, str]:
+  """Return a tiny canned fact for the dispatched researcher."""
+  facts = {
+      'adk': "ADK is Google's Agent Development Kit for building agents.",
+      'gemini': "Gemini is Google's family of multimodal models.",
+  }
+  key = topic.strip().lower()
+  return {
+      'topic': topic,
+      'fact': facts.get(key, f'No canned fact for {topic}.'),
+  }
+
+
+dispatcher = AgentDispatcherToolset(
+    model='gemini-2.5-flash',
+    tool_allowlist={'lookup_fact': lookup_fact},
+)
+
+root_agent = Agent(
+    name='orchestrator',
+    model='gemini-2.5-flash',
+    instruction="""\
+You coordinate research by dispatching specialist agents.
+
+When the user asks for research:
+1. Call dispatch_agent (background by default) with name, instruction, user_message.
+   Optionally pass tool_names=["lookup_fact"]. Use wait=true only if you must block.
+2. You may dispatch multiple specialists in parallel, then call await_agent per id.
+3. For follow-ups, call message_agent with the same dispatch_id.
+4. Use get_agent_result to poll status without waiting.
+
+Keep the user updated with a concise final answer.
+""",
+    tools=[dispatcher],
+)

src/google/adk/tools/__init__.py

@@ -53,6 +53,10 @@
 _LAZY_MAPPING = {
     'AuthToolArguments': ('..auth.auth_tool', 'AuthToolArguments'),
     'AgentTool': ('.agent_tool', 'AgentTool'),
+    'AgentDispatcherToolset': (
+        '.agent_dispatcher._agent_dispatcher_toolset',
+        'AgentDispatcherToolset',
+    ),
     'APIHubToolset': ('.apihub_tool.apihub_toolset', 'APIHubToolset'),
     'BaseTool': ('.base_tool', 'BaseTool'),
     'DiscoveryEngineSearchTool': (

src/google/adk/tools/agent_dispatcher/__init__.py

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+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Runtime agent dispatch tools for orchestrators."""
+
+from ._agent_dispatcher_toolset import AgentDispatcherToolset
+
+__all__ = ['AgentDispatcherToolset']