fix(sessions): archiving a live session stops its pane

Archive on a session a live pane held only hid its row, and the list
deliberately does not bring such a tab back, so the pane kept running
with nothing on screen showing it — a member archived five sessions
believing them closed and kept ~2.7 GB of claude/omp/postgres-mcp alive
for up to two days. Archive on a live session is now a Stop (endRuns,
the tab X's confirm, DELETE /api/run/:id?archive=1) in the sidebar row,
the workspace home's Recents and their right-click menu.

client/src/components/__tests__/WorkspaceTree.test.tsx

@@ -3,7 +3,8 @@
  * @description Tests for the sidebar's workspace list: one flat row per
  * workspace in the stored order, a row expanding to its sessions (remembered),
  * a live session opening its pane and an ended one its transcript, the
- * workspace's OWN sessions only, a session's state dot, rename and archive,
+ * workspace's OWN sessions only, a session's state dot, rename and archive
+ * (a live one's pane stopped first),
  * selection
  * by URL, Alt+arrow reordering kept in localStorage, double-click rename, the
  * search, the row menu's items by kind and tool, the status dot, and the
@@ -225,6 +226,8 @@ describe("WorkspaceTree", () => {
     await user.type(input, "Better name{Enter}");
     expect(api.sessions.patch).toHaveBeenCalledWith("s-old", { name: "Better name" });
     await user.click(screen.getByTestId("workspace-session-archive-s-live"));
+    // A live session's Archive stops its pane first — never a hidden pane left running.
+    expect(api.run.kill).toHaveBeenCalledWith("agenthub-lane-1-2", { archive: true });
     expect(api.sessions.patch).toHaveBeenCalledWith("s-live", { archived: true });
   });