POST /dt/start, stamped dt.start whatever its body names, forwarded to the
plugin and answered with its dt.opened or dt.error. The plugin remembers the
key; DT despawns its own chest; nothing is kept here. dt.started, dt.won and
dt.ended ride the feed like any other event (docs rust-link/PROTOCOL.md §20.8).
72 tests (one new), fmt and clippy clean.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E14m6SuuY6i1vASFeGDBeY
