2026-01-08: Duo agentic chat in the Web doesn't respond when using default "GitLab Duo" agent

Duo agentic chat in the Web doesn't respond when using default "GitLab Duo" agent (Severity 3)

Problem: Duo agentic chat in the web became unresponsive when using the default 'GitLab Duo' agent, with the websocket connection stuck and not progressing.

Impact: The Duo agentic chat in the web was unresponsive for users with the 'mcp_client' feature flag enabled (mainly GitLab team members) when using the default 'GitLab Duo' agent. General users were not impacted, and switching to a different agent or disabling the flag allowed continued use.

Causes: The issue was caused by the 'mcp_client' feature flag, which was enabled for GitLab team members. This flag caused requests to the chat agent to fail when using the default 'GitLab Duo' agent. Disabling the flag immediately restored functionality.

Response strategy: We disabled the 'mcp_client' feature flag globally, which immediately restored chat functionality. Deployments are now unblocked.

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This ticket was created to track INC-6492, by incident.io 🔥