Explain why Chat /research cannot open, and keep the draft until it does

Briefs longer than the composer accepts are refused in Chat. The launcher
returns a cause-specific result after the document has laid out, so the
Chat draft clears only once the composer holds the brief: an open draft
offers Go to it, read-only and reconnecting say so, and transient causes
offer Retry. The caret lands after a prefilled brief, and @chopin
/research is the same command.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>