Add `aid=$pid` to 133;A and 133;D for nested shell tracking, and fix the
state comparison which was incorrectly using `constantly` (comparing a
string to a function, which always evaluated to true).
OSC 133;B (input start) and 133;P;k=r (right prompt) cannot be reliably
implemented at the script level because Elvish escapes control
characters in prompt function output, and writing directly to /dev/tty
has timing issues because Elvish renders its prompts on a background
thread. Full semantic prompt support requires a native implementation:
https://github.com/elves/elvish/pull/1917
See: #10523
1d76820937