Local player gets frozen in place when FPS and ping are above a threshold

[pierow]

Having high FPS and ping results in the local player being visually stuck in place and the game unplayable until the player lowers their frame rate. This is caused by a prediction buffer on the client that holds client cmd entries being too small. Right now it holds 64 cmds. This can hopefully be increased without server or mod changes, as the SDK doesn't seem to rely on this, and the server doesn't run into this issue as it uses its update rate to fill its position history buffers, and the player still moves around on the server.

Demonstration:

https://github.com/user-attachments/assets/e56691ec-dd54-4389-9f35-06379189a8f6

This issue happens on normal dedicated servers with real latency as well. The values entered for fakelag here don't represent the resulting ping.

Fixing this would be a big help for smaller communities that play intercontinentally. I've gotten complaints about this from players in my mod, and I've managed to fix all the unrelated fps dependent issues in a dev build, so this is an annoying barrier.

Increasing this buffer to 512 should cover pretty much all cases, but 256 should work up to 1000fps and ~180ms ping (256ms theoretical, but having a latency and fps combo that is just under the threshold of the game being unplayable also results in some subtle prediction errors).

Side note: If entities are seen disappearing when testing this at high fps, it is due to a different entity position history bug that is less of an issue and is easily remedied by lowering the ex_interp value. Most players and mods should do this anyway. https://github.com/ValveSoftware/halflife/issues/395#issuecomment-808231541