[5/8] Add executor process transport for MCP stdio by aibrahim-oai · Pull Request #18088 · openai/codex

aibrahim-oai · 2026-04-16T06:12:32Z

Summary

Add an rmcp transport backed by executor process read/write calls.
Add an executor stdio launcher that starts non-tty processes with piped stdin.

Stack

o  #18027 [8/8] Fail exec client operations after disconnect
│
o  #18025 [7/8] Cover MCP stdio tests with executor placement
│
o  #18089 [6/8] Wire remote MCP stdio through executor
│
@  #18088 [5/8] Add executor process transport for MCP stdio
│
o  #18087 [4/8] Abstract MCP stdio server launching
│
o  #18020 [3/8] Add pushed exec process events
│
o  #18086 [2/8] Support piped stdin in exec process API
│
o  #18085 [1/8] Add MCP server environment config
│
o  main

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chatgpt-codex-connector · 2026-04-16T06:19:16Z

+                Err(broadcast::error::RecvError::Lagged(skipped)) => {
+                    warn!(
+                        "Remote MCP server output stream lagged ({}): skipped {skipped} events",
+                        self.program_name
+                    );
+                    self.closed = true;
+                }


Recover lagged event streams instead of terminating transport

RecvError::Lagged means this receiver skipped broadcast entries, not that the process is dead. The code sets closed = true, which makes receive() return EOF and triggers transport shutdown, aborting otherwise healthy MCP sessions during bursty output. Since ExecProcess also exposes retained read() data, this path should resync (or fail explicitly) rather than force-close.

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chatgpt-codex-connector · 2026-04-16T06:26:06Z

+            Err(error) => {
+                debug!(
+                    "Failed to parse remote MCP server message ({}): {error}",
+                    self.program_name
+                );
+                None
+            }


Drain buffered frames after parse errors

take_stdout_message drops an invalid line and returns None, then receive_message immediately waits on events.recv(). If a single output chunk contains bad\n{valid-json}\n, the valid JSON frame remains in self.stdout but is never processed until another event arrives. A quiet server can then stall MCP initialization until timeout.

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chatgpt-codex-connector · 2026-04-16T06:26:24Z

+
+impl ExecutorProcessTransport {
+    pub(super) fn new(process: Arc<dyn ExecProcess>, program_name: String) -> Self {
+        let events = process.subscribe_events();


Replay missed process events before awaiting broadcast

ExecutorProcessTransport::new subscribes to process.subscribe_events() only after start() has already returned. If the child exits immediately, Closed/Failed can be emitted before this subscription and are not replayed by broadcast. receive_message() then waits on events.recv() with closed == false, which can stall MCP handshake/reads indefinitely for dead-on-start servers.

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github-actions · 2026-04-16T07:18:06Z

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

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chatgpt-codex-connector · 2026-04-16T07:24:27Z

+                LaunchedStdioServerTransport::Executor { transport } => (
+                    service::serve_client(client_service, transport).boxed(),
+                    None,
+                    None,


Terminate executor process when handshake setup fails

Add cleanup parity with local stdio: this branch keeps no guard/owner for the spawned executor process. If serve_client errors or time::timeout elapses during initialization, the future is dropped and the process can remain running without a later terminate(), leaking MCP subprocesses across retries.

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Add an rmcp transport and runtime that bridge stdio bytes through the executor process API. Co-authored-by: Codex <noreply@openai.com>

aibrahim-oai mentioned this pull request Apr 16, 2026

[5/8] Add executor process transport for MCP stdio #17987

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aibrahim-oai force-pushed the dev/remote-mcp-stdio-runtime branch from b440257 to c603449 Compare April 16, 2026 06:20

aibrahim-oai force-pushed the dev/remote-mcp-executor-stdio branch from f6e61df to f11cc84 Compare April 16, 2026 06:20

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edward-bayes marked this pull request as draft April 16, 2026 07:18

edward-bayes marked this pull request as ready for review April 16, 2026 07:19

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aibrahim-oai force-pushed the dev/remote-mcp-stdio-runtime branch from c603449 to db32dd3 Compare April 16, 2026 13:55

aibrahim-oai force-pushed the dev/remote-mcp-executor-stdio branch from 0af64c7 to aad254a Compare April 16, 2026 13:56

Add executor-backed rmcp stdio transport

ad686d6

Add an rmcp transport and runtime that bridge stdio bytes through the executor process API. Co-authored-by: Codex <noreply@openai.com>

aibrahim-oai force-pushed the dev/remote-mcp-executor-stdio branch from aad254a to ad686d6 Compare April 16, 2026 13:59

aibrahim-oai force-pushed the dev/remote-mcp-stdio-runtime branch from db32dd3 to 2ccbd13 Compare April 16, 2026 13:59

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[5/8] Add executor process transport for MCP stdio#18088

[5/8] Add executor process transport for MCP stdio#18088
aibrahim-oai wants to merge 1 commit intodev/remote-mcp-stdio-runtimefrom
dev/remote-mcp-executor-stdio

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aibrahim-oai commented Apr 16, 2026 •

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