Problem: Supplying any `platforms` table silently dropped all unlisted
platforms, making it easy to accidentally disable platforms. Disabled
platforms also produced no user-facing error on invocation.
Solution: Switch to a merge model — all six platforms are enabled by
default and user entries are deep-merged on top. Set a platform key to
`false` to disable it explicitly. Add a `check_platform_enabled` guard
in `handle_command` for contest fetch, login, logout, and race actions.
Barrett Ruth
1c8b5cda3e
