openai/codex · error

events/list returned an unexpected MCP result

Error message

events/list returned an unexpected MCP result

What it means

Error "events/list returned an unexpected MCP result" thrown in openai/codex.

Source

Thrown at codex-rs/codex-mcp/src/resource_client.rs:247

        Ok(McpResourceReadResult { contents })
    }

    /// Lists the events advertised by the hosted Plugin Runtime.
    pub async fn list_events(&self) -> Result<McpEventCatalogSnapshot> {
        let (connections, _) = self
            .runtime
            .latest_connections_for_event_server(CODEX_APPS_MCP_SERVER_NAME)?;
        let cache_key = McpResourceClientCacheKey(Arc::downgrade(&connections));
        let (managed, request_timeout) = connections
            .client_by_name(CODEX_APPS_MCP_SERVER_NAME)
            .await?;
        let result = managed
            .client
            .send_custom_request_with_timeout("events/list", /*params*/ None, request_timeout)
            .await
            .context("events/list failed for hosted Plugin Runtime")?;
        let ServerResult::CustomResult(result) = result else {
            return Err(anyhow!("events/list returned an unexpected MCP result"));
        };
        let result = result
            .result_as::<McpEventListResult>()
            .context("events/list returned invalid event definitions")?;

        Ok(McpEventCatalogSnapshot {
            cache_key,
            events: result.events,
        })
    }

    /// Opens an MCP event subscription with the supplied event arguments.
    pub async fn open_event_stream(
        &self,
        event_name: &str,
        arguments: &Value,
        request_meta: Option<&Map<String, Value>>,
    ) -> Result<McpEventStream> {

View on GitHub (pinned to 339751715c)

Solutions

1. Fix the MCP server to return a spec-conformant result for events/list.

When it happens

Trigger: Thrown at codex-rs/codex-mcp/src/resource_client.rs:247 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of openai/codex@339751715c (2026-08-25). Data as JSON: /api/errors/16d2238b1eb8d1a2. Report an issue: GitHub.