X_MCP_CATALOG_TOOL_DUPLICATE
Means
a per-caller MCP catalog names one tool twice
Typical cause
defineAppMcp({ catalog }) resolved a tool whose name a static tool, a meta tool, list_tenants or another runtime tool already answers to
Fix
defineAppMcp({ catalog: (caller) => ({ tools: [runtimeTool({ name: '<unique-name>', … })] }) }) — rename the runtime tool; x mcp tools --json lists the static names