> Another useful command to check for open file descriptors is lsof,
... but the one that comes with the operating system, on the BSDs, is fstat(1).
> 10u: Another file descriptor [...] likely used for additional terminal interactions.
The way that ZLE provides its user interface, and indeed what the Z shell does with the terminal in general, is quite interesting; and almost nothing like what one would expect from old books on the Bourne shell.
> it tries to open more files than the soft limit set by my shell
Your shell can change limits, but it isn't what is originally setting them. That is either the login program or the SSH daemon. On the BSDs, you can read about the configuration file that controls this in login.conf(5).
... but the one that comes with the operating system, on the BSDs, is fstat(1).
> 10u: Another file descriptor [...] likely used for additional terminal interactions.
The way that ZLE provides its user interface, and indeed what the Z shell does with the terminal in general, is quite interesting; and almost nothing like what one would expect from old books on the Bourne shell.
> it tries to open more files than the soft limit set by my shell
Your shell can change limits, but it isn't what is originally setting them. That is either the login program or the SSH daemon. On the BSDs, you can read about the configuration file that controls this in login.conf(5).