Root build scripts, the desktop bundle and the dev:web watcher pass the
native loader so tsdown never selects the undeclared unrun fallback. A spec
covers the build.ts rejection path.
Without process.features.typescript, tsdown falls back to the undeclared
unrun loader, which fails to import and, once installed, resolves
import.meta.url in packages/client/tsdown.client.ts to the entry config.
Refs #5622