Then build a supervisor that reconciles running tmux sessions against a
declared set.

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:   Swift
Package:    libtmux-swift (Swift Package Index)
Repository: https://github.com/libtmux/libtmux-swift

Read these before writing code:
- https://libtmux.org/en/swift/latest/llms.txt
  every page for Swift, as a list
- https://libtmux.org/en/swift/latest/docs.json
  the same list with headings, as JSON
- https://libtmux.org/en/swift/latest/reference/
  the Swift 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 Swift project yet, start one:
       swift package init --type executable
   Skip this in a project that already exists, and match what is here.
3. Add the dependency. libtmux-swift has no stable release. 0.1.0-alpha.6 is
   the newest prerelease on Swift Package Index, and the command below names it
   because the resolver skips prereleases otherwise.
       .package(url: "https://github.com/libtmux/libtmux-swift", exact: "0.1.0-alpha.6")
   Check https://swiftpackageindex.com/libtmux/libtmux-swift for a newer
   version, and prefer a stable release over this one if there now is any.
   A target depends on the product, not the package: write .product(name:
   "LibTmux", package: "libtmux-swift"). The library is `LibTmux` while the
   package identity SwiftPM derives from the URL is `libtmux-swift`, which
   is neither the product name nor the `name:` in the package manifest.
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.

Session supervisor

What it does:
- Reads a declared set of sessions and windows from a file.
- Compares it against what the server is running and reports the difference
  before changing anything.
- Applies the difference: creates what is missing, and leaves alone anything
  already correct.
- Has a dry-run mode that prints the plan and touches nothing.

Constraints:
- Converge. Running it repeatedly against an unchanged server must do nothing
  the second time and say so.
- Never kill a window it did not create unless I pass an explicit flag.
- Compare against the server's own state rather than against a file this tool
  wrote last time.
- Report what changed in terms I can read, not a diff of internal structures.

Anchor it in these pages:
- https://libtmux.org/en/tmux/concepts/workspaces/
  workspaces
- https://libtmux.org/en/tmux/concepts/queries/
  queries
- https://libtmux.org/en/tmux/guides/querying-and-filtering/
  querying and filtering