Bug: Viewport requirement makes completion detection flaky #459

Currently HTML blocks (maybe others) require the whole block to be in the viewport to trigger the completion timer (default 5 seconds). This is confusing, and blocks with lots of content can become impossible to complete on some screens (or any screen at extreme lengths). This results in a lot of "completion works on your machine but not mine" and "completion worked earlier, but doesn't now" when someone resizes a window or opens dev tools.

I don't have any hard solutions for a replacement, but some options are:

• Scrap the viewport check entirely
• Trigger the timer when the block scrolls into view at all instead
• Trigger the timer (with a shorter time?) when the bottom of the block scrolls into view