Thank you for catching! Fixed in changeset/183878212

My fix is still in review and hasn't made it into upstream Valhalla yet, so the upstream maintainers of Valhalla are asking to revert this change for now. I'm a bit concerned this will hide the underlying bug in Valhalla but I was able to extract a pretty small extract of the OSM data to reproduce the bug which should allow us to test the fix independently of this change being rolled back.

I'm not sure there's a minimum per se, but I think it's somewhat unusual to have so many points around a corner like this. Might be best to ask in the OSM discord! https://discord.gg/openstreetmap

For what it's worth, this change revealed a very subtle bug in Valhalla and I was able to submit a patch to fix it :): https://github.com/valhalla/valhalla/pull/5529

https://github.com/valhalla/valhalla/issues/5521 for further discussion on the downstream breakage.

This change seems to have broken Valhalla, and has added a significant number of nodes, in some cases hundreds of nodes within meters of each other along ways. E.g. node/13148097576#map=19/45.646311/-74.360544