[BUG] google-ads-mcp: DEVELOPER_TOKEN_INVALID / missing credential error only when invoked via Claude Code, works fine standalone

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Summary

Calling any tool from the official google-ads-mcp server
(github.com/googleads/google-ads-mcp) via Claude Code's MCP tool-call
mechanism consistently fails with an authentication error, even though the
exact same credentials work perfectly when the server is invoked outside
Claude Code.

Environment

• Claude Code: VSCode native extension
• MCP server: google-ads-mcp (official, github.com/googleads/google-ads-mcp), v0.0.1
• Auth: Application Default Credentials (gcloud auth application-default login

with a custom OAuth client + https://www.googleapis.com/auth/adwords scope)

• Developer token: Basic Access approved

Error (identical every time, regardless of what's changed below)

_InactiveRpcError: UNAUTHENTICATED - "Request is missing required
authentication credential..."
errors { error_code { authentication_error: DEVELOPER_TOKEN_INVALID } }

What I tried (all failed identically via Claude Code)

1. Original .mcp.json entry using uvx --from git+https://github.com/googleads/google-ads-mcp.git google-ads-mcp
2. Explicitly setting GOOGLE_APPLICATION_CREDENTIALS to the ADC file path
3. Patching the package locally to always use google.auth.default()

(removing a code path that checks fastmcp.server.dependencies.get_access_token()
first and prefers it over ADC when truthy)

1. Registering the server under a brand-new name (google-ads-patched) to

rule out any server-identity caching

1. Copying the ADC credentials file into the project directory instead of

~/.config/gcloud/..., in case of a subprocess sandbox file-access restriction

1. Full app restart (Cmd+Q) after every change above

What DOES work (proving credentials/token/setup are correct)

• A direct curl call to https://googleads.googleapis.com/v24/customers:listAccessibleCustomers

using the ADC access token + developer token header → HTTP 200, correct customer IDs returned.

• Launching the exact same google-ads-mcp server as a subprocess manually

(same command/args/env as .mcp.json) and calling it via fastmcp.Client

• StdioTransport from a plain Python script → succeeds, returns the

correct customer IDs.

• Only calls routed through Claude Code's own MCP tool-call path fail, with

byte-identical error text across every variant above.

Suspected cause

Something in how Claude Code spawns/sandboxes MCP server subprocesses
differs from a bare subprocess launch — possibly network egress restriction
to googleads.googleapis.com, or an env/credential-file access restriction
that isn't hit by other MCP servers (e.g. meta-ads, an HTTP-transport
server, works fine).

Request

Any guidance on how Claude Code sandboxes stdio MCP subprocess network/file
access, and whether that can be adjusted for a specific server, would help
narrow this down further.

What Should Happen?

Please refer to above

Error Messages/Logs

Please refer to above

Steps to Reproduce

Please refer to above

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.217

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Other

Additional Information

FYI, I'm using Antigravity IDE.