threads=0 Misconfiguration Silently Hangs Waitress-Backed Flask Servers

A common but hard-to-spot misconfiguration in Waitress-backed Flask apps involves setting the threads parameter to 0, leaving the server with no worker threads to process incoming requests. The server starts normally, binds its port, and logs nothing unusual, yet every request hangs indefinitely without any error message. This typically occurs when an environment variable is unset, a config file contains a typo, or a CPU-based thread calculation rounds down to zero on a low-resource container. Because Waitress does not raise an exception for threads=0 at startup, the bug only becomes apparent once requests begin failing silently. The StayPresent library addresses this by validating the threads value before the server starts, immediately throwing a ValueError for any value below 1 to make misconfiguration obvious and easier to debug.