A turn that ends without a final `todo` update left the composer "Tasks N/M"
panel pinned with its last item stuck pending/in_progress, and it survived
restarts because the panel is read back from stored session history.
Two coupled fixes (the first alone is undone by the second path):
- Turn end: clear a still-active todo list on `message.complete` and on a
terminal `error` (new `clearActiveSessionTodos` — active lists only; a
finished list keeps its short linger so the last checkmark still lands).
- Rehydration: `hydrateFromStoredSession` runs *after* a turn completes, so an
"active" stored list is stale, not in-flight. It now restores only a
*finished* list (via new `todosForHydration`) and drops anything still
active — otherwise it re-pinned the panel right after the turn-end clear and
resurrected it on every restart.
Salvages #52996 (@0disoft): the fix shape (clearActiveSessionTodos on turn
completion, preserving the finished-list linger) is carried forward and ported
onto the current use-message-stream/ folder split (gateway-event.ts), then
extended to the rehydration path per review.
Co-authored-by: 0disoft <rodisoft1@gmail.com>
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