Callers from outside the app now get a parameter error for a key a
command's params description doesn't name, instead of the command
running with its defaults: `text.select {story, start, end}` and
`style.list {bogus: 1}` are refused with "unknown parameter `…`" and the
nearest or the accepted keys.
- engine: `cmd::params` (ported from VectorCraft #1442) reads the keys
from each params description; `check_params` / `check_keys`.
`Session::execute` itself stays lenient so old journals replay; in the
engine's own tests it checks too, as the audit of the descriptions.
- MCP: tools/call answers -32602 for an argument a tool doesn't take and
for params a command doesn't take (`execute`, every `batch` step before
the first runs); the headless backend checks as well.
- Control channel (`engine.execute`) and `designcraft-cli run --cmd`.
- Descriptions now name every key their commands read (table target
cells, anchored objects, gap.move, file.place, data merge, prefs.set,
…); type.char / type.para stay unchecked (their attributes may be the
params object itself; the setters refuse unknown attributes).
- Tests that passed keys the commands never read are fixed, and the pen
tool no longer sends the unread `notifyPen`.
Fixes#776
Gert Pellin