Bind failure: uWSGI socket listener component

Goal is to validate integration behavior without production credentials by observing documented uWSGI startup failure conditions early in a test harness.

The socket listener component is documented to prevent master process start when the configured socket path or port is already in use or not permitted. Bind outcomes depend on OS user and filesystem permissions rather than uWSGI internals, and flags and defaults are version sensitive for the core listener.

There is uncertainty about how bind failure is distinguished from other startup aborts and what signals are available to a test harness that must remain credential-free.

What conditions cause the master process to abort startup versus defer? What observable signals indicate a bind failure versus a permission denial for the socket listener? What is the documented interaction between listener failure and worker spawn in the Python plugin path?