Add `RemoteMcpServer`, a server-side remote MCP tool for `ManagedAgent`. The
Managed Agents / Interactions API runs the MCP server itself, so ADK only
forwards the server URL and headers as an `MCPServerParam` and never opens an
MCP session. A `header_provider` callback (the same contract as the `LlmAgent`
`McpToolset.header_provider`) mints auth headers at request time, driven by the
runner, and is merged over any static headers so a fresh token can be generated
per turn.
Only remote (HTTP/streamable) MCP servers are supported; raw
`types.Tool.mcp_servers` remains rejected. Includes a live integration test
against Maps Grounding Lite, scoped to the Gemini Developer API backend; the
Vertex Interactions endpoint does not yet accept the `mcp_server` tool param
(consistent with google-genai documenting `types.Tool.mcp_servers` as
unsupported on Vertex AI).
Co-authored-by: Haran Rajkumar <haranrk@google.com>
PiperOrigin-RevId: 945306712
Haran Rajkumar
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