feat: add support for custom requests #590
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modelcontextprotocol#580 and modelcontextprotocol#556 introduced support for custom notifications, so this PR takes the next logical step and adds support for custom requests: - Introduces `CustomRequest` and `CustomResult` model types, wires them into the client/server request and result unions, and allows `ClientRequest::method()` to return the dynamic method name. - Implements serde and meta handling for `CustomRequest` so `_meta` is carried through extensions; adds default `on_custom_request` handlers that return `METHOD_NOT_FOUND` unless overridden. - Updates JSON schema fixtures to include the new request/result shapes and `EmptyObject` strictness. - Adds tests for custom request roundtrips and end-to-end client↔server handling. - Focused integration test in `crates/rmcp/tests/test_custom_request.rs`. For additional testing, I used this locally to update Codex to use a custom request instead of a custom notification so that it gets an "ack" from the MCP server to ensure it has processed the update before sending more messages: openai/codex#8142.
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Version `0.12.0` includes modelcontextprotocol/rust-sdk#590, which I will use in #8142. Changes: - `rmcp::model::CustomClientNotification` was renamed to `rmcp::model::CustomNotification` - a bunch of types have a `meta` field now, but it is `Option`, so I added `meta: None` to a bunch of things
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…st (#8142) Historically, `accept_elicitation_for_prompt_rule()` was flaky because we were using a notification to update the sandbox followed by a `shell` tool request that we expected to be subject to the new sandbox config, but because [rmcp](https://crates.io/crates/rmcp) MCP servers delegate each incoming message to a new Tokio task, messages are not guaranteed to be processed in order, so sometimes the `shell` tool call would run before the notification was processed. Prior to this PR, we relied on a generous `sleep()` between the notification and the request to reduce the change of the test flaking out. This PR implements a proper fix, which is to use a _request_ instead of a notification for the sandbox update so that we can wait for the response to the sandbox request before sending the request to the `shell` tool call. Previously, `rmcp` did not support custom requests, but I fixed that in modelcontextprotocol/rust-sdk#590, which made it into the `0.12.0` release (see #8288). This PR updates `shell-tool-mcp` to expect `"codex/sandbox-state/update"` as a _request_ instead of a notification and sends the appropriate ack. Note this behavior is tied to our custom `codex/sandbox-state` capability, which Codex honors as an MCP client, which is why `core/src/mcp_connection_manager.rs` had to be updated as part of this PR, as well. This PR also updates the docs at `shell-tool-mcp/README.md`.
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#580 and #556 introduced support for custom notifications,
so this PR takes the next logical step and adds support for custom requests:
CustomRequestandCustomResultmodel types, wires them into the client/serverrequest and result unions, and allows
ClientRequest::method()to return the dynamic methodname.
CustomRequestso_metais carried throughextensions; adds default
on_custom_requesthandlers that returnMETHOD_NOT_FOUNDunlessoverridden.
EmptyObjectstrictness.
crates/rmcp/tests/test_custom_request.rs.For additional testing, I used this locally to update Codex to use a custom
request instead of a custom notification so that it gets an "ack" from the MCP
server to ensure it has processed the update before sending more messages:
openai/codex#8142.