* fix(frontend): resolve stale subagent running state after stop
Subtask cards were recreated from task tool calls as in_progress whenever
the thread was loading. If a user stopped a run before the task tool returned
a ToolMessage, the card could remain running after reload, and could flip back
to running when a later user turn started streaming.
Derive pending subtask state from the current assistant turn instead of the
global thread loading flag. A task now stays in progress only while its own
turn is loading or while a matching ToolMessage exists for result parsing;
otherwise it is marked failed.
Add unit coverage for task ToolMessage matching and for the later-turn loading
regression.
* fix(frontend): refresh subagent card on terminal status transition
- notify React via a ref + post-render effect when a subtask flips to
completed/failed, so SubtaskCard updates without relying on an
unrelated MessageList re-render
- tighten the current-turn heuristic to `groupIndex === lastGroupIndex`
(precomputed once) — fixes the rare case where an earlier subagent
group in the same turn was kept in_progress, and drops the per-group
slice+some scan to O(1)
- rename `getPendingSubtaskStatus` → `derivePendingSubtaskStatus`
- narrow `toolCall.id` at MessageList call sites; skip task tool calls
without an id instead of `id!`
- add Playwright e2e covering reload-after-stop showing `Subtask failed`
