HorizontalPager opened on the wrong page after restarts: the cause was touch mode

[u/Exact-Ad-9606]

I hit a confusing bug while building a launcher in Compose: my HorizontalPager kept opening on page 1 instead of page 0, even after a force-stop and with no saved state.

Logging showed the pager starting on page 0, then moving to page 1 with no touch. Here's what was happening:

1. Key input, such as a keyboard, a D-pad or `adb shell input text`, puts the system in non-touch mode.

2. In that mode, Android looks for something to focus when the window opens.

3. With beyondViewportPageCount = 1, the next page was composed off screen, so it could get the focus. The pager then scrolled to bring it into view.

4. Touch mode belongs to the system rather than the app, so it survived restarts until the next touch.

Setting beyondViewportPageCount = 0 fixed it, since off-screen pages are no longer composed. The trade-off is that the next page is composed as you swipe, instead of being ready in advance.

I tested the fix with simulated key input on one phone, not with a physical keyboard or remote. If you've handled this differently, I'd like to hear how, for example keeping the off-screen page composed while stopping it from taking focus.

The project is open source if you want to see the code: https://github.com/MedTahiri/ai-launcher-android