`SDK_RENDERERS` and `RUN_CODE_FLAVORS` had to stay in step by review alone:
the `Object.hasOwn` guards catch drift only once a runtime reporting the
half-added language exists, which is the one case that cannot arise. Both
tables are now `satisfies`-checked against a shared `CodeSdkLanguage` union,
so a missing or extra entry fails `typecheck`. The declared `Record<string, …>`
type stays, since `CodeRuntime.language` is an unconstrained `string`.
The code-runtime seam's own README row and `CodeRuntime.language` JSDoc still
named `'typescript'` as the sole well-known value; both now name `'python'`
too and say only `'typescript'` has a published backend.
Chinesezjc