codex - 💡(How to fix) Fix tool_call_mcp_elicitation=false does not suppress elicitation.form in MCP initialize (Graylog handshake fails with -32603) [1 participants]

What version of Codex CLI is running?

codex-cli 0.120.0

What subscription do you have?

Pro

Which model were you using?

gpt-5.3-codex

What platform is your computer?

Linux 6.8.0-106-generic x86_64 x86_64

What terminal emulator and version are you using (if applicable)?

running in a generic Ubuntu Linux shell environment

What issue are you seeing?

When starting Codex with a configured Graylog MCP server, MCP startup fails during handshake with:

MCP client for `graylog` failed to start: MCP startup failed: handshaking with MCP server failed: JSON-RPC error: -32603: Unrecognized field "form" (class io.modelcontextprotocol.spec.McpSchema$ClientCapabilities$Elicitation), not marked as ignorable (0 known properties: ]) at [Source: UNKNOWN; byte offset: #UNKNOWN] (through reference chain:

io.modelcontextprotocol.spec.McpSchema$InitializeRequest["capabilities"] >io.modelcontextprotocol.spec.McpSchema$ClientCapabilities["elicitation"]->io.modelcontextprotocol.spec.McpSchema$ClientCapabilities$Elicitation["form"])

Then Codex shows:

⚠ MCP startup incomplete (failed: graylog)

Reproduction details

Direct request to Graylog MCP endpoint with elicitation.form reproduces the server-side failure:

curl -i -X POST \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-03-26","capabilities":{"elicitation": {"form":true}},"clientInfo":{"name":"probe","version":"1.0"}}}' \  
"http://<REDACTED_TOKEN>:[email protected]:9000/api/mcp"

Response:

HTTP/1.1 500 Internal Server Error
  
{"jsonrpc":"2.0","id":1,"error":{"code":-32603,"message":"Unrecognized field \"form\" ..."}}

Control check (no elicitation.form) succeeds:

curl -i -X POST \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-03-26","capabilities":{},"clientInfo": {"name":"probe","version":"1.0"}}}' \
 "http://<REDACTED_TOKEN>:[email protected]:9000/api/mcp"

Response:

HTTP/1.1 200 OK
 
{"jsonrpc":"2.0","id":1,"result":{"protocolVersion":"2025-06-18",...}}

Why this looks like a Codex bug

I disabled the feature flag but Codex still appears to send elicitation.form during startup:

codex features list | rg tool_call_mcp_elicitation

tool_call_mcp_elicitation        stable             false

Also tested launch override:

codex -c features.tool_call_mcp_elicitation=false

Result is unchanged: same MCP startup handshake failure with elicitation.form.

Environment

• Codex CLI: @openai/codex 0.120.0
• OS: Ubuntu Linux shell
• Graylog: 7.0.6+711d207 (MCP endpoint at /api/mcp)

What steps can reproduce the bug?

1. Configure Graylog MCP server in Codex:

codex mcp add graylog --url "http://<REDACTED_TOKEN>:[email protected]:9000/api/mcp"

1. Confirm elicitation feature is disabled:

codex features disable tool_call_mcp_elicitation
codex features list | rg tool_call_mcp_elicitation

--> expected: false

1. Start a new Codex session (or force at launch):

codex -c features.tool_call_mcp_elicitation=false

1. Observe startup output.

Actual result

Codex still fails MCP handshake for Graylog with:

JSON-RPC error: -32603: Unrecognized field "form" ... ClientCapabilities$Elicitation["form"]
⚠ MCP startup incomplete (failed: graylog)

Control check (server behavior)

• initialize without capabilities.elicitation.form succeeds (HTTP 200).
• initialize with capabilities.elicitation.form fails (HTTP 500, -32603).

What is the expected behavior?

When tool_call_mcp_elicitation is disabled (either in config or via -c features.tool_call_mcp_elicitation=false), Codex should not include capabilities.elicitation.form in MCP initialize requests.

As a result:

• Graylog MCP handshake should complete successfully.
• Codex should start without:
  • MCP client for 'graylog' failed to start
  • ⚠ MCP startup incomplete (failed: graylog)

Additional information

• Graylog auth/connectivity are working:
  • POST /api/mcp with valid auth and a minimal initialize payload returns HTTP 200.
• The failure is specific to capabilities.elicitation.form.
• Graylog was upgraded from 7.0.5 to 7.0.6; behavior is unchanged.
• As a temporary workaround, I used a local proxy shim that strips capabilities.elicitation.form from initialize before forwarding to Graylog. With that shim, handshake succeeds and Codex can use Graylog MCP.
• This strongly suggests either:
  1. Codex still sends elicitation form despite the feature flag being disabled, or
  2. the flag is not applied to MCP startup handshake payload generation.