diff --git a/frontend/src/shared/state/capstress.test.ts b/frontend/src/shared/state/capstress.test.ts
new file mode 100644
index 00000000..b8269399
--- /dev/null
+++ b/frontend/src/shared/state/capstress.test.ts
@@ -0,0 +1,76 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import reducer, { reconcileSessions, removeCard, bringToFront } from '@/shared/state/dashboardLayoutSlice';
+
+function seed(n: number) {
+  let s: any = reducer(undefined, { type: '@@init' });
+  const want: Record<string, { x: number; y: number }> = {};
+  for (let i = 0; i < n; i++) {
+    const id = 'c' + i, x = 100 + i * 31, y = 200 + i * 17;
+    want[id] = { x, y };
+    s = reducer(s, { type: 'dashboardLayout/placeCard',
+      payload: { sessionId: id, x, y, width: 480, height: 280, expandedSessionIds: [], exact: true } });
+  }
+  return { s, want, ids: Object.keys(s.cards) };
+}
+const lost = (s: any, ids: string[], want: any) =>
+  ids.filter((id) => !s.cards[id] || s.cards[id].x !== want[id].x || s.cards[id].y !== want[id].y).length;
+
+test('STRESS: flaky backend, 30 strip/restore cycles on a 200-card board', () => {
+  const { s, want, ids } = seed(200);
+  let cur: any = s;
+  for (let r = 0; r < 30; r++) {
+    cur = reducer(cur, reconcileSessions({ sessionIds: [], expandedSessionIds: [] }));
+    cur = reducer(cur, reconcileSessions({ sessionIds: ids, expandedSessionIds: [] }));
+  }
+  console.log(`    200 cards, 30 flaps -> lost=${lost(cur, ids, want)} closedPos=${Object.keys(cur.closedCardPositions).length}`);
+  assert.equal(lost(cur, ids, want), 0);
+});
+
+test('STRESS: half the board vanishes and returns, repeatedly', () => {
+  const { s, want, ids } = seed(120);
+  const half = ids.slice(0, 60);
+  let cur: any = s;
+  for (let r = 0; r < 40; r++) {
+    cur = reducer(cur, reconcileSessions({ sessionIds: ids.slice(60), expandedSessionIds: [] }));
+    cur = reducer(cur, reconcileSessions({ sessionIds: ids, expandedSessionIds: [] }));
+  }
+  console.log(`    120 cards, 40 half-flaps -> lost=${lost(cur, ids, want)} closedPos=${Object.keys(cur.closedCardPositions).length}`);
+  assert.equal(lost(cur, ids, want), 0);
+});
+
+test('STRESS: long life, 3000 distinct cards churned, map stays bounded', () => {
+  let cur: any = reducer(undefined, { type: '@@init' });
+  for (let i = 0; i < 3000; i++) {
+    cur = reducer(cur, { type: 'dashboardLayout/placeCard',
+      payload: { sessionId: 'z' + i, x: i, y: i, width: 480, height: 280, expandedSessionIds: [] } });
+    cur = reducer(cur, bringToFront({ id: 'z' + i, type: 'agent' }));
+    cur = reducer(cur, reconcileSessions({ sessionIds: [], expandedSessionIds: [] }));
+  }
+  const cp = Object.keys(cur.closedCardPositions).length;
+  const zo = Object.keys(cur.zOrders).length;
+  console.log(`    3000 cards churned -> closedPos=${cp} zOrders=${zo}`);
+  assert.ok(cp <= 1000, `closedCardPositions unbounded at ${cp}`);
+  assert.equal(zo, 0, `zOrders leaked ${zo} entries`);
+});
+
+test('STRESS: mixed usage, explicit close + reconcile + refocus interleaved', () => {
+  // An EXPLICIT close (you pressed X) deliberately does not record a position, unlike a session
+  // vanishing, so a card resurrected afterwards lands in a fresh cell BY DESIGN. This asserts the
+  // invariant that actually matters here (no card is lost) and prints the position count without
+  // asserting it, because asserting 0 would encode a behaviour we do not want. The first version of
+  // this test asserted only presence while printing lostSpot=25, i.e. it would have stayed green
+  // through a real scattering regression; the split is the point.
+  const { s, want, ids } = seed(80);
+  let cur: any = s;
+  for (let r = 0; r < 25; r++) {
+    cur = reducer(cur, bringToFront({ id: ids[r % ids.length], type: 'agent' }));
+    cur = reducer(cur, removeCard(ids[r % ids.length]));
+    cur = reducer(cur, reconcileSessions({ sessionIds: ids, expandedSessionIds: [] }));
+  }
+  const survivors = ids.filter((id) => cur.cards[id]);
+  const moved = lost(cur, ids, want);
+  console.log(`    80 cards, 25 explicit close+resurrect -> present=${survivors.length} movedByDesign=${moved}`);
+  assert.equal(survivors.length, 80, 'cards went missing under mixed usage');
+  assert.ok(moved <= 25, `${moved} cards moved, more than the 25 that were explicitly closed`);
+});