Eclipse AssistAI MCP tool calls fail with "Unexpected response type" from 0.139.0 onward

Open 💬 1 comment Opened Jul 16, 2026 by robertrath-spiraldatagroup

What version of Codex CLI is running?

0.140.4

What subscription do you have?

ChatGPT Plus

Which model were you using?

gpt-5.4

What platform is your computer?

Linux 6.8.0-134-generic x86_64 x86_64

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

_No response_

Codex doctor report

What issue are you seeing?

Registered MCP tool calls to an Eclipse MCP server fail with:

Unexpected response type

The regression begins with @openai/codex@0.139.0.

The same Eclipse MCP server, Eclipse workspace, Codex configuration and read-only search request work correctly with @openai/codex@0.138.0.

The MCP tools are successfully discovered and are visible to Codex, but invoking them fails.

Known version results:

@openai/codex@0.138.0: works
@openai/codex@0.139.0: fails
@openai/codex@0.144.4: fails

The issue affects multiple tools, including:

eclipse_ide.fileSearchRegExp
eclipse_ide.fileSearch
eclipse_context.listCachedResources

What steps can reproduce the bug?

Environment:

OS: Linux
Component: Codex CLI
Installation method: npm installation into a temporary prefix
Test directory: ~/docker
MCP transport: Streamable HTTP
MCP server: Eclipse MCP server
Eclipse plugin name: Assist AI
Eclipse plugin version: 1.0.7.202607151807
Eclipse feature ID: com.github.gradusnikov.eclipse.assistai.feature.group
Provider: WojciechGradkowski

Use a non-sensitive Eclipse workspace containing a Dockerfile.

Start Codex 0.138.0 from the workspace:

/tmp/codex-old-test/node_modules/.bin/codex \
"try a filesearch for Dockerfile in the current Eclipse project using the eclipse mcp server"

Codex calls an Eclipse MCP search tool, for example:

eclipse_ide.fileSearchRegExp({
"pattern": ".+",
"fileNamePatterns": "Dockerfile"
})

or:

eclipse_ide.fileSearch({
"containingText": "FROM",
"fileNamePatterns": "Dockerfile"
})

Confirm that the search succeeds with @openai/codex@0.138.0.

Repeat the same test with @openai/codex@0.139.0 or @openai/codex@0.144.4.

The tool call then fails with:

Error: tool call error: tool call failed for eclipse_ide/fileSearchRegExp

Caused by:
Unexpected response type

The non-search MCP tool eclipse_context.listCachedResources also fails in 0.139.0:

Called eclipse_context.listCachedResources({})

Error: tool call error: tool call failed for eclipse_context/listCachedResources

Caused by:
Unexpected response type

With 0.144.4, both Eclipse search tools fail:

Called eclipse_ide.fileSearchRegExp({
"pattern": ".+",
"fileNamePatterns": "Dockerfile"
})

Error: tool call error: tool call failed for eclipse_ide/fileSearchRegExp

Caused by:
Unexpected response type
Called eclipse_ide.fileSearch({
"containingText": "FROM",
"fileNamePatterns": "Dockerfile"
})

Error: tool call error: tool call failed for eclipse_ide/fileSearch

Caused by:
Unexpected response type

What is the expected behavior?

The registered MCP tool call should complete successfully and return the Eclipse search results.

For example, with @openai/codex@0.138.0:

Called eclipse_ide.fileSearchRegExp({
"pattern": ".+",
"fileNamePatterns": "Dockerfile"
})

[SearchResult[file=L/Docker/build/Dockerfile, lineNumber=1, ...]]

Codex 0.139.0 and later should accept and process the same MCP server response that is accepted by Codex 0.138.0.

Additional information

The version bisect result is:

0.138.0 works
0.139.0 fails
0.144.4 fails

The failure appears to be in the Codex registered MCP tool-call response-handling path.

Tool discovery still works, so the Eclipse MCP tools remain visible and callable from Codex. The failure occurs after a tool is invoked, when Codex processes the returned response.

Because the same MCP server and search operation succeed with 0.138.0 but fail beginning with 0.139.0, this appears to be a Codex CLI regression introduced in version 0.139.0.

A successful example using version 0.138.0 is as follows:

› try a filesearch for Dockerfile in the current Eclipse project using the eclipse mcp server

• I’m going to locate the Eclipse MCP tools first, then run a file search for Dockerfile in the current project and report what it finds.

• Called eclipse_ide.fileSearch({"containingText":"FROM","fileNamePatterns":"Dockerfile*"})
└ [SearchResult[file=L/Docker/build/Dockerfile, lineNumber=1, lineContent=FROM ubuntu:24.04]]

────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────

• Found one Dockerfile in the Eclipse workspace:

L/Docker/build/Dockerfile at line 1: FROM ubuntu:24.04

If you want, I can search for additional Docker-related files like docker-compose.yml or other Dockerfile* variants.

An unsuccessful example using version 0.140.4 is as follows:

› try a filesearch for Dockerfile in the current Eclipse project using the eclipse mcp server

• I’m going to locate the Eclipse MCP tools first, then use its file search capability to look for Dockerfile in the current project.

• I found the Eclipse file search tool. I’m querying files named Dockerfile directly in the workspace so we get the actual matches rather than content guesses.

• Called eclipse_ide.fileSearchRegExp({"pattern":".+","fileNamePatterns":"Dockerfile"})
└ Error: tool call error: tool call failed for eclipse_ide/fileSearchRegExp
Caused by:
Unexpected response type

• The first query failed at the tool layer, so I’m switching to a more specific search term inside Dockerfile files to verify whether any exist.

• Called eclipse_ide.fileSearch({"containingText":"FROM","fileNamePatterns":"Dockerfile"})
└ Error: tool call error: tool call failed for eclipse_ide/fileSearch
Caused by:
Unexpected response type

• I’m importing the workspace directory into Eclipse first in case the project wasn’t opened in the IDE context yet, then I’ll retry the search.

◦ Calling eclipse_ide.openProject({"directoryPath":"/home/robert/docker"})

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