ArrowUp/Down (and Escape) in handleKeyPress only check `isSlashCommandModeActive`, not `hasSlashCommandCandidates`. When the slash trigger activates but no commands match (e.g. typing `hello /unknownword`, or any `/word` token after whitespace that isn't a known command), `SlashCommandPopup` renders nothing yet `preventDefault()` is still fired — so multiline cursor navigation is silently broken whenever a non-matching slash token is in the draft. The fix is to add the same `&& hasSlashCommandCa

Selecting a slash command rewrites controlledText via handleSelectSlashCommand without adjusting any mention indices, so any mention whose start ≥ slashCommandStartIndex now points at the wrong substring of the new text. This corrupts the immediately-stored draft (textAndMentionsToContent slices from stale offsets, dropping characters and duplicating mention text) and can silently lose mentions on the next keystroke when handleMention's display-equality check fails. Fix by shifting mention.start