Problem/Motivation #3585882 changed the default MCP endpoint to /mcp, but several docs and in-repo references still say /_mcp, so following the README and POSTing to /_mcp returns a 404. /mcp is the intended default: the route subscriber overrides the /_mcp still declared in mcp_server.routing.yml, and McpRouteSubscriberKernelTest asserts /mcp. So this is a doc/placeholder cleanup, not a behavior change. The follow-up was noted in #3585882 but never landed. Proposed resolution Align every remaining /_mcp reference to /mcp: Docs: README.md, modules/mcp_server_oauth/README.md, AGENTS.md, references/auth/index.md, references/sdk/server-lifecycle.md. Config/comments: the mcp_server.routing.yml placeholder (annotated as overridable via mcp_server.base_path), mcp_server.permissions.yml, two *.services.yml comments, and the McpExceptionSubscriber docblock. Test: the synthetic request path in McpServerControllerTest. No behavior change.