# Open questions

Decisions deliberately left open, with what is known so far, so they can be
picked up without redoing the research.

## Where does an unknown command word run?

Raised 2026-09-27 in the review of pardes against acme (Plan 9 source at
`~/05-genizah/principia-softwarica`). Undecided.

**Today.** A middle-click, an `exec` write or a tag word that is not a builtin
is typed into a terminal pane: the pane itself when it takes a command line,
else a shell for the pane's directory (`execute`, `ttyForDir` in
`src/exec.zig`). The command shares that shell's cwd, environment, history
and aliases, and its output lands in the terminal.

**acme.** An external command runs as its own process: stdin from
`/dev/null`, stdout and stderr to the directory's `+Errors` window, `$winid`
and `%` set for it (`editors/acme/exec.c`, `run()` and its callers around
:1180-1300 and :1425). No shell state is shared between commands.

**What each costs.**

* Typing into a shell: interactive programs work, and so do aliases and
  functions. But every command depends on that shell's state (is it busy,
  which directory it is in, what was typed at its prompt), and a misspelled
  builtin silently becomes a shell command. The 9P `exec` file cannot report
  that the command failed.
* A process per command: the misspelling hazard goes away at the root, the
  editor knows each command's exit status and output, and `exec` could answer
  the way `pty/run` does. But aliases, shell functions and interactive
  programs need a terminal of their own, and output goes to a `+Errors`-style
  buffer rather than a live terminal.

**Evidence from use (2026-09-28).** A fresh agent driving pardes through
9P wrote a misspelled word to `exec`; it was typed into a terminal's fish
shell ("Unknown command"), nothing reached `log`, and the write succeeded.
Its report ranked this among the confusing behaviours.

**Related.** `pty/run` (see `docs/fs.md`) already gives an agent the second
behaviour inside a chosen terminal: a line in, `exit N` and its output out.
The planned root `ctl` (session builtins) and pane `ctl` (pane builtins)
refuse unknown words, whatever is decided here; the question is only what
`exec` and the middle-click do with them.