fix: change codex/sandbox-state/update from a notification to a request by bolinfest · Pull Request #8142 · openai/codex

bolinfest · 2025-12-16T22:39:05Z

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 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.

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.

#580 and #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.

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

bolinfest · 2025-12-16T22:39:05Z