Entry point modules not being re-used, chunks generated unnecessarily?

[Here's a quick scenario](https://hyrious.me/esbuild-repl/?version=0.14.42&mode=build&modules=%5B%5B%22button.js%22%2C%22export+function+Button%28%29+%7B%5Cn%5Ctreturn+%5C%22button%5C%22%3B%5Cn%7D%22%2C1%5D%2C%5B%22main.js%22%2C%22import+%7B+Button+%7D+from+%5C%22.%2Fbutton.js%5C%22%3B%5Cnexport+default+function+App%28%29+%7B%5Cn%5Ctreturn+Button%28%29%3B%5Cn%7D%22%2C1%5D%5D&buildOptions=%7B%22bundle%22%3Atrue%2C%22format%22%3A%22esm%22%2C%22splitting%22%3Atrue%7D)

Where I have _two_ entrypoints, `button.js` and `main.js`. `main.js` imports from `button.js`. I would've expected two output modules -- one for button, one for main, with main importing from button. Instead, esbuild builds an extra chunk that both main.js and button.js import from.

Why is this extra chunk necessary, instead of main.js reusing the button.js entrypoint module?

Thanks!

Start with the linked esbuild REPL scenario using button.js and main.js, with bundle, esm format, and splitting enabled. Inspect the generated entry modules and shared chunk to understand the reported behavior. Done means documenting whether the extra chunk is expected or identifying a concrete change needed.

Written by the indexing model from the issue text.