--watch mode leaving without watching

Hello,

Putting ```"watch": "tsup --watch"```, in my package.json scripts and running it only does the build and leave right after insead of watching for changes.
Tsup output shows "CLI Running in watch mode".

tsup.config.ts:
```typescript
import { defineConfig } from 'tsup';
import { EXECUTABLE_NAME } from './src/consts';

export default defineConfig({
entry: {
[EXECUTABLE_NAME]: 'src/index.ts',
},
target: 'node22',
format: 'cjs',
outDir: '.',
treeshake: true,
// minify: true,
});
```

Reproduce the issue using the package.json watch script and the supplied tsup.config.ts, then observe why the process exits after the initial build despite reporting watch mode. Verify the behavior by changing src/index.ts while the command runs. Done means the command stays active and rebuilds when source files change.

Written by the indexing model from the issue text.