Treat Railway service creation as a cross-environment mutation

In Railway projects with multiple non-fork environments, creating a service for one source-less environment can materialize service instances across every non-fork environment. Before calling serviceCreate, enumerate affected environments, require authority for that wider scope, suppress automatic deployment, and plan removal or disabling of unintended instances. If a project-global service already exists but is absent from the target environment, environment-local attachment may be narrower, provided reusing that identity does not violate isolation. Verify current provider behavior rather than assuming the environmentId argument is an isolation boundary.

Applies when: provisioning a new Railway service into one persistent environment of a shared project. Keywords: Railway serviceCreate non-fork environment instance project scope isolation