Then build a watcher that waits for output in a tmux pane and acts on it.

libtmux drives a real tmux server from code. It gives you objects for the
server, its sessions, windows and panes. Documentation for every language
is at https://libtmux.org/en/.

Language:   C++
Package:    libtmux-cxx (its repository)
Repository: https://github.com/libtmux/libtmux-cxx

Read these before writing code:
- https://libtmux.org/en/cxx/latest/llms.txt
  every page for C++, as a list
- https://libtmux.org/en/cxx/latest/docs.json
  the same list with headings, as JSON
- https://libtmux.org/en/cxx/latest/reference/
  the C++ API reference
If you cannot fetch URLs, clone the repository above and read its README
and examples instead, or ask me to paste those pages in.

Set up first:
1. Report the tmux version with `tmux -V`. libtmux drives a real tmux, so
   nothing below works without one. Stop and tell me if it is missing.
2. If this directory is not a C++ project yet, write a CMakeLists.txt
   declaring cmake_minimum_required and project(), targeting C++23.
   Skip this in a project that already exists, and match what is here.
3. Add the dependency. libtmux-cxx is not published to its registry yet, so
   this installs from the repository at tag v0.1.0-alpha.11.
       include(FetchContent)
       FetchContent_Declare(libtmux-cxx
         GIT_REPOSITORY https://github.com/libtmux/libtmux-cxx
         GIT_TAG v0.1.0-alpha.11)
       FetchContent_MakeAvailable(libtmux-cxx)
   Check https://github.com/libtmux/libtmux-cxx for a newer version, and
   prefer a stable release over this one if there now is any.
4. Write the smallest program that proves the install works: connect to a
   tmux server, create a session, confirm it is there, then kill it. Give
   that server a socket of its own rather than using the default one, so
   this never touches a tmux I am already running. Run it, and show me the
   output and the files you added.

Rules for everything below:
- Use the reference above rather than guessing names. The ten libtmux
  ports do not share spellings, and a name from another language will look
  plausible and not exist.
- If the reference does not have something you expected, say so instead of
  writing a call that does not exist.
- Follow the conventions already in this repository.

Output watcher

What it does:
- Watches one or more panes for a pattern I give it.
- Runs an action when the pattern appears: print it, run a command, or send
  input back into that pane.
- Keeps watching after a match, so a long-running build that prints several
  interesting lines produces several events.

Constraints:
- Do not poll on a fixed interval if this port offers a way to be notified.
  Say which mechanism you used and why.
- Do not miss output that arrives between two reads, and do not report the same
  line twice. Say how your approach avoids both.
- Match against text that has already had terminal escapes handled, so a
  pattern does not fail on invisible bytes.
- Give it a timeout, and make a timeout a result the caller can handle.

Anchor it in these pages:
- https://libtmux.org/en/tmux/guides/capturing-output/       capturing output
- https://libtmux.org/en/tmux/examples/capture-pane-output/  capture pane output
- https://libtmux.org/en/tmux/concepts/transports/           transports