Codex CLI 0.145.0 tool calls return `unsupported call` despite successful MCP handshake with matlab-mcp-server v0.11.2

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Title

Codex CLI 0.145.0 tool calls return unsupported call despite successful MCP handshake with matlab-mcp-server v0.11.2

Environment

• Client: Codex CLI codex-cli 0.145.0 (npm package), Windows 11
• Server: matlab-mcp-server-windows-x64.exe v0.11.2 (at D:\/AI\/matlab-mcp-server-windows-x64.exe)
• MATLAB: R2024a at D:\/Program Files\/MATLAB\/R2024a\/bin\/matlab.exe (on PATH)
• Server session mode: new (no toolbox dependency)
• Display mode: nodesktop

Symptom

All mcp__matlab__* tool calls (detect_matlab_toolboxes, evaluate_matlab_code, check_matlab_code, run_matlab_file, run_matlab_test_file) return:

unsupported call: mcp__matlab__<tool-name>

The five tools are listed in the Codex function registry (visible to the model), but every invocation is rejected client-side before any request reaches the server.

Evidence: server never sees the calls

Server log (%TEMP%\matlab-mcp\server-<session-id>.log) shows clean startup but no tool-call entries ever appear, even after repeated calls:

[INFO] Initiating application startup, version: github.com/matlab/matlab-mcp-server v0.11.2
[INFO] Configuration state, UseSingleMATLABSession:true, InitializeMATLABOnStartup:true,
       MATLABDisplayMode:nodesktop, MATLABSessionMode:new, ...
[INFO] Application directory state, log-dir:..., id:<session>
[INFO] Application startup complete
[INFO] Added tools to MCP SDK server, count:5
[INFO] Added additional tools to MCP SDK server, count:0
[INFO] Added resources to MCP SDK server, count:2
[INFO] New client session, client-name:"codex-mcp-client", client-title:"Codex",
       client-version:"0.145.0"
[WARN] Error evaluating if the path was a symbolic link, path:"",
       error:"GetFileAttributesEx C:\Users\Administrator: The system cannot find the file specified."
[WARN] Error evaluating if the path was a symbolic link, path:"",
       error:"CreateFile C:\WINDOWS\system32\config\systemprofile: Access is denied."

After invoking mcp__matlab__check_matlab_code(...):

• Server log file size and line count do not change.
• Two matlab-mcp-server-windows-x64.exe processes remain alive.
• codex mcp list continues to show matlab ... enabled.

Codex-side observation

codex doctor reports a clean environment: CODEX_HOME = C:\Users\Chen_\.codex, config.toml parse: ok, 1 MCP server (1 stdio), 0 disabled, auth: configured.

The error string unsupported call: mcp__matlab__<name> does not appear in the server log; it is produced by the Codex client dispatcher.

What we have ruled out

• ❌ config.toml parse error (codex doctor: ok)
• ❌ Missing WINDIR env var (already configured, see config below)
• ❌ MATLAB not on PATH (D:\/Program Files\/MATLAB\/R2024a\/bin\/matlab.exe resolves)
• ❌ Wrong binary name (matches matlab-mcp-server-<os>-<arch>[.exe] from v0.11.0+)
• ❌ Wrong tool names (all 5 match README §Tools)
• ❌ Server crash on startup (processes alive, log shows clean init)
• ❌ Missing MATLAB MCP Server Toolbox (not required for --matlab-session-mode=new)
• ❌ MATLAB session init failure (server log shows no MATLAB init entry either way; failure mode is "Codex rejects the call", not "MATLAB connection timeout")

Config (verbatim)

[mcp_servers.matlab]
command = 'D:\/AI\/matlab-mcp-server-windows-x64.exe'
args = ["--matlab-display-mode=nodesktop", "--matlab-session-mode=new",
       '--initial-working-folder=D:\/NUT\我的坚果云\/9.他人资料\/李富豪',
       "--initialize-matlab-on-startup=true", "--disable-telemetry=true",
       '--log-folder=C:\/Users\/Chen_\/AppData\/Local\/Temp\/matlab-mcp']

[mcp_servers.matlab.env]
WINDIR = 'C:\/WINDOWS'

Questions

1. Is there a known compatibility issue between Codex CLI 0.145.0's MCP client and matlab-mcp-server v0.11.2? Note that the Codex v0.145.0 changelog mentions new VS Code extension enabledApiProposals such as chatSessionsProvider and languageModelProxy, which suggests recent client-side MCP changes.
2. Is there a recommended way to enable client-side debug logging to capture the raw JSON-RPC frames Codex sends (or to confirm it is not sending any)? Adding --log-level=debug on the server side does not help here, because the requests never reach the server.
3. The --initialize-matlab-on-startup=true flag is set, but the server log records no MATLAB init success or failure line after startup. Is silent failure of MATLAB init on Windows + stdio transport + Codex 0.145.0 a known issue?

Workarounds tried (no effect)

• Multiple repeated mcp__matlab__* calls → all return unsupported call
• Switching between simplest (detect_matlab_toolboxes with no args) and richer (evaluate_matlab_code with code + project_path) calls → identical client-side rejection

Reference

The Windows-specific WINDIR env-var requirement from the README Codex section (linked to issue #32 in the README) has been applied; that does not resolve the issue.

[ybenouag]

Hi @qreerjack-svg, thanks for the very detailed report. The ruled-out list and the server logs are genuinely helpful.

Based on the evidence, this looks like a client-side Codex dispatch issue rather than a matlab-mcp-server bug. The unsupported call: mcp__matlab__<tool> string is produced by Codex's own tool router (codex-rs/core/src/tools/registry.rs) when an incoming tool call does not match its handler registry. That is consistent with what you are seeing: the request is rejected before it ever reaches the server, which is why the server log shows a clean handshake but no tool-call entries.

There are several open Codex issues describing this exact symptom. The common thread is a custom model provider using wire_api = "responses" backed by a non-OpenAI model, where the flattened mcp__<server>__<tool> name does not get re-associated with its namespace, so the lookup misses. One of them is filed against this server:

• [Bug] MCP dynamic tool proxy returns unsupported call for all MCP tools openai/codex#22970 (MATLAB MCP plus a proxied model, same unsupported call: mcp__matlab__)
• unsupported call: mcp__<server>__<tool> for MCP tools when used with custom Responses API provider (Apps SDK + custom model) openai/codex#31354 (clearest root-cause writeup)
• MCP tools return 'unsupported call' with custom Responses API provider (llama.cpp) openai/codex#26977
• MCP unsupported call openai/codex#30902

Could you help us narrow it down:

1. Your [model_providers] block and the model you are using. The config you posted does not include them. So far this only reproduces on custom Responses-API providers with non-OpenAI models.
2. As a quick check, does the same MCP config work if you point Codex at an OpenAI-native model? On our side we could not reproduce it with Codex 0.145.0 against an OpenAI-native model. The tool calls succeed, which points upstream rather than at the server.

If it turns out to be the custom-provider path, the fix would need to land in Codex. The issues above are the ones to follow.
Thanks a lot
Yannis

[github-actions]

We are still waiting on the information requested above. If we don't hear back within 7 days, this issue will automatically be closed.