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codex - 💡(How to fix) Fix [Bug] MCP dynamic tool proxy returns unsupported call for all MCP tools

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MCP server connection works (resources can be listed and read), but all MCP dynamic tools (mcp__matlab__, mcp__node_repl__) return unsupported call when invoked.

Error Message

  1. Observe error: unsupported call: mcp__matlab__ / unsupported call: mcp__node_repl__
  • Any MCP dynamic tool call (mcp__matlab__, mcp__node_repl__) fails with unsupported call error ERROR|codex_core::tools::router|...:dispatch_tool_call_with_code_mode_result{ error=unsupported call: mcp__matlab__

Root Cause

MCP server connection works (resources can be listed and read), but all MCP dynamic tools (mcp__matlab__, mcp__node_repl__) return unsupported call when invoked.

Fix Action

Fix / Workaround

  • list_mcp_resources - returns resources correctly
  • read_mcp_resource - reads resource content correctly
  • All built-in Codex tools (shell, apply_patch, etc.) work fine
  • MCP server logs show list_all_tools succeeded and tools were registered

From Codex SQLite logs:

ERROR|codex_core::tools::router|...:dispatch_tool_call_with_code_mode_result{
  otel.name=mcp__matlab__ tool_name=mcp__matlab__ ...}: 
  error=unsupported call: mcp__matlab__

Code Example

ERROR|codex_core::tools::router|...:dispatch_tool_call_with_code_mode_result{
  otel.name=mcp__matlab__ tool_name=mcp__matlab__ ...}: 
  error=unsupported call: mcp__matlab__
RAW_BUFFERClick to expand / collapse

Description

MCP server connection works (resources can be listed and read), but all MCP dynamic tools (mcp__matlab__, mcp__node_repl__) return unsupported call when invoked.

Environment

  • Codex version: 26.513.31313 (Desktop, Windows)
  • OS: Windows
  • Model provider: Custom (DeepSeek V4 via cc-switch proxy at localhost:3000)
  • wire_api: responses (also tested chat - same result)
  • MCP servers: MATLAB MCP Core Server v0.9.1, Node REPL

Steps to Reproduce

  1. Configure any MCP server in config.toml (tested with MATLAB Agentic Toolkit and Node REPL)
  2. Start Codex session
  3. Verify MCP connection works: list_mcp_resources returns resources from the MCP server successfully
  4. Try calling an MCP tool: mcp__matlab__ or mcp__node_repl__
  5. Observe error: unsupported call: mcp__matlab__ / unsupported call: mcp__node_repl__

What Works

  • list_mcp_resources - returns resources correctly
  • read_mcp_resource - reads resource content correctly
  • All built-in Codex tools (shell, apply_patch, etc.) work fine
  • MCP server logs show list_all_tools succeeded and tools were registered

What Does Not Work

  • Any MCP dynamic tool call (mcp__matlab__, mcp__node_repl__) fails with unsupported call error
  • The model correctly emits function calls with proper arguments, but Codex tool router rejects them

Log Evidence

From Codex SQLite logs:

ERROR|codex_core::tools::router|...:dispatch_tool_call_with_code_mode_result{
  otel.name=mcp__matlab__ tool_name=mcp__matlab__ ...}: 
  error=unsupported call: mcp__matlab__

Expected Behavior

MCP tools should be callable just like built-in tools.

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#api#task chaining#parallel task#integration issue#index setup

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