Slack seals a native stream server-side after a few minutes (live-observed
at ~5m20s on three independent long turns, 2026-09-15/16; the lifetime is
not documented). The next chat.appendStream on the card fails with
message_not_in_streaming_state. The adapter returned a bare failure, the
TurnRunner latched native_failed, and the rest of the turn rendered as an
edited text bullet list. Long autonomous turns lost the card UX exactly
when it mattered.
On message_not_in_streaming_state from appendStream, drop the dead
stream_ts and chat.startStream a fresh plan-mode card in the same thread,
then append the current frame there. Every frame already carries the full
visible task projection, so no task state is lost. One reopen per update;
a second rejection surfaces as a real failure. The sealed card is a plain
message now, so no stopStream is sent to it; the turn-final stop targets
the reopened card. Error matching reads SlackApiError.response["error"],
never the message text.
Tests assert the wire sequence (start, append, rejected append, start,
append on the new ts), the reopened frame's task states, the cache pointing
at the new card, and the stop targeting it; plus the one-reopen bound.
Mutation: forcing the expiry branch off turns both tests red.
5648f81431