Accept MCP elicitation requests so headless MCP tool calls work

[principalwater]

Fixes #640.

Problem

Every MCP tool call inside a plugin-driven run (/codex:rescue, codex-companion.mjs task) fails immediately. The job log shows only:

Calling my-server/my.tool.
Tool my-server/my.tool failed.

The rollout under ~/.codex/sessions/ has the real cause:

{"type": "mcp_tool_call_end",
 "invocation": {"server": "my-server", "tool": "my.tool", ...},
 "duration": {"secs": 0, "nanos": 0},
 "result": {"Err": "user rejected MCP tool call"}}

duration is 0 — the call never leaves the client.

Cause

Codex gates MCP tool calls behind an MCP elicitation (mcpServer/elicitation/request), not the exec/patch approval channel. So the approvalPolicy: "never" that buildThreadParams already sets for every thread this client starts does not cover them.

handleServerRequest answered every server-initiated request with -32601:

handleServerRequest(message) {
  this.sendMessage({
    id: message.id,
    error: buildJsonRpcError(-32601, `Unsupported server request: ${message.method}`)
  });
}

That leaves the elicitation unresolved, and codex-rs/core/src/mcp_tool_call.rs maps a missing response to ReviewDecision::Abort, surfaced as user rejected MCP tool call. Runs driven by this client are headless, so nobody can accept interactively and every MCP tool call fails.

The user-visible symptom is misleading: the agent concludes its MCP servers are unreachable and works without them. In my case that was a memory server the agent is instructed to consult before non-trivial work — it silently proceeded without project context and reported the memory as unavailable, which sent me looking for a networking problem that did not exist.

Change

Answer mcpServer/elicitation/request with action: "accept", per McpServerElicitationRequestResponse in codex-rs/app-server-protocol. Everything else still gets -32601.

The response logic moves into an exported pure function buildServerRequestResponse() so it can be tested directly — AppServerClientBase is not exported, so there was no way to reach the old method from a test. handleServerRequest is now one line.

Verification

Unit — new tests/app-server.test.mjs, 3 cases, all passing: elicitation is accepted, unimplemented server requests still get -32601, request id type is preserved.

End to end — same plugin task calling an MCP memory server, before and after the change:

	before	after
Task result	FAIL user rejected MCP tool call	OK 1
user rejected MCP tool call in job log	3	0

Note: tests/state.test.mjs has one failing case (resolveStateDir uses a temp-backed per-workspace directory) that reproduces on pristine main and is unrelated to this change.

Note for maintainers

Independently of this fix, propagating the real error text into the job log and /codex:status would help a lot. Tool <server>/<tool> failed. gave no hint that approval was involved — diagnosing this required reading raw rollout JSONL.

[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: 36abd9cc08

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[principalwater]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. 🎉

Reviewed commit: 2fb936efb9

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[principalwater]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Swish!

Reviewed commit: 2fb936efb9

ℹ️ About Codex in GitHub

Codex has been enabled to automatically review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

When you sign up for Codex through ChatGPT, Codex can also answer questions or update the PR, like "@codex address that feedback".