Salvaged from #32340 by @LeonSGP43, adapted to the workspace-scoped
status tracking that landed in #63709:
- /stop with no running agent now best-effort clears the platform
status indicator, so a phantom 'is thinking...' left by a gateway
restart or a turn that died without a final send can always be
dismissed (#32295).
- SlackAdapter.stop_typing clears an untracked thread when the caller
names it explicitly in metadata — clearing an unset status is a
harmless no-op on Slack's side. The fallback is skipped when multiple
Slack Connect workspaces track the same channel+thread and no team_id
is given, preserving #63709's cross-workspace safety guarantee.
In a per-user thread (thread_sessions_per_user=True), each participant
gets an isolated session key (...:{thread_id}:{user_id}). A run another
user started lives under a different key, so the caller's own /stop found
nothing and replied 'no active task to stop'.
When /stop finds no run under the caller's own key, fall back to
interrupting any running agent(s) sharing the caller's thread prefix
({chat_id}:{thread_id}), gated on _is_user_authorized. Thread-only — the
fallback returns [] for non-thread channels, and a prefix-collision guard
prevents thr1 from matching thr11.
