`md` forwards every argument to marktext untouched except two flags of its
own: `--read-only`/`-r` and `--foreground`. By default it detaches via
`bkg`, so the shell stays usable and the editor outlives the window that
launched it.
MarkText has no read-only mode, so `-r` sandboxes it with firejail, binding
each named file read-only. The subtlety is that MarkText is single-instance:
a plain launch hands the file to an already-running, unsandboxed, writable
window and exits, silently defeating the sandbox. `-r` therefore also passes
a private `--user-data-dir`, which forces an independent instance the
read-only bind actually covers, plus `--no-sandbox`, since Electron's own
sandbox needs the user namespaces firejail has already taken away.
Flags whose entire purpose is terminal output (`--version`, `-v`/`--verbose`,
`--debug`) imply `--foreground`; backgrounding them would send the output
you asked for to /dev/null.
The function is autoloaded and so never shadows an `md` function or alias
defined elsewhere -- fish only looks in functions/ when nothing named `md`
exists. A real `md` *binary* would be shadowed, so the body hands off to it
verbatim whenever marktext is not installed. No conf.d file and no
opinionated guard: `md` is a novel name rather than a command shadow, the
same as `bkg` and `detach`.
