message: also look backwards into commands for last word to tab-complete
diff: @@ -306,7 +306,11 @@ export default class BasicMessageEditor extends React.Component {
  const position = model.positionForOffset(caret.offset, caret.atNodeEnd);
  const range = model.startRange(position);
  range.expandBackwardsWhile((index, offset, part) => {
  - return part.text[offset] !== " " && (part.type === "plain" || part.type === "pill-candidate");
  + return part.text[offset] !== " " && (
  + part.type === "plain" ||
  + part.type === "pill-candidate" ||
  + part.type === "command"
  + );
  });
  const {partCreator} = model;
  // await for auto-complete to be open
  