parseSlashCommand used /^(\S+)\s*(.*)$/ where `.` can't cross a newline and
`$` anchors end-of-string, so any slash command whose arg contained a newline
(/goal <multi-line text>, a skill command with a long pasted context) failed
the whole match, parsed as an empty name, and rendered "empty slash command"
while the payload vanished — cleared from the composer and absent from the
Up-arrow history ring, which only derives from sent user messages.
- name now splits on any whitespace ([\s\S]* arg), matching the CLI and the
gateway's split(maxsplit=1); multiline args flow to slash.exec intact
- the residual empty-name branch (bare "/", "/ text") restores the submitted
text to the composer draft instead of eating it
Fixes#41323. Fixes#55510.
fb44b519d7