chore: import upstream snapshot with attribution

contributing/samples/mcp/mcp_dynamic_header_agent/README.md

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+This agent connects to a local MCP server via Streamable HTTP and provides
+custom per-request headers to the MCP server.
+
+To run this agent, start the local MCP server first by running:
+
+```bash
+uv run header_server.py
+```

contributing/samples/mcp/mcp_dynamic_header_agent/__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/mcp/mcp_dynamic_header_agent/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.
+
+
+from google.adk.agents.llm_agent import LlmAgent
+from google.adk.tools.mcp_tool.mcp_session_manager import StreamableHTTPConnectionParams
+from google.adk.tools.mcp_tool.mcp_toolset import McpToolset
+
+root_agent = LlmAgent(
+    name='tenant_agent',
+    instruction="""You are a helpful assistant that helps users get tenant
+ information. Call the get_tenant_data tool when the user asks for tenant data.""",
+    tools=[
+        McpToolset(
+            connection_params=StreamableHTTPConnectionParams(
+                url='http://localhost:3000/mcp',
+            ),
+            tool_filter=['get_tenant_data'],
+            header_provider=lambda ctx: {'X-Tenant-ID': 'tenant1'},
+        )
+    ],
+)

contributing/samples/mcp/mcp_dynamic_header_agent/header_server.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 __future__ import annotations
+
+from fastapi import Request
+from mcp.server.fastmcp import Context
+from mcp.server.fastmcp import FastMCP
+
+mcp = FastMCP('Header Check Server', host='localhost', port=3000)
+
+TENANT_DATA = {
+    'tenant1': {'name': 'Tenant 1', 'data': 'Data for tenant 1'},
+    'tenant2': {'name': 'Tenant 2', 'data': 'Data for tenant 2'},
+}
+
+
+@mcp.tool(
+    description='Returns tenant specific data based on X-Tenant-ID header.'
+)
+def get_tenant_data(context: Context) -> dict:
+  """Return tenant specific data."""
+  if context.request_context and context.request_context.request:
+    headers = context.request_context.request.headers
+    tenant_id = headers.get('x-tenant-id')
+    if tenant_id in TENANT_DATA:
+      return TENANT_DATA[tenant_id]
+    else:
+      return {'error': f'Tenant {tenant_id} not found'}
+  else:
+    return {'error': 'Could not get request context'}
+
+
+if __name__ == '__main__':
+  try:
+    print('Starting Header Check MCP server on http://localhost:3000')
+    mcp.run(transport='streamable-http')
+  except KeyboardInterrupt:
+    print('\nServer stopped.')