diff --git a/frontend/src/app/pages/Dashboard/controls/CardSearchPalette.tsx b/frontend/src/app/pages/Dashboard/controls/CardSearchPalette.tsx
index 19dbfd97..4873b677 100644
--- a/frontend/src/app/pages/Dashboard/controls/CardSearchPalette.tsx
+++ b/frontend/src/app/pages/Dashboard/controls/CardSearchPalette.tsx
@@ -37,6 +37,8 @@ const CardSearchPalette: React.FC<Props> = ({
   const items = useMemo((): CardSearchItem[] => {
     const result: CardSearchItem[] = [];
     for (const card of Object.values(cards)) {
+      // A layout entry without a session cannot be searched or focused; one such entry took the whole palette down on every render.
+      if (typeof card.session_id !== 'string') continue;
       const session = sessions[card.session_id];
       result.push({
         id: card.session_id,
diff --git a/frontend/src/shared/state/dashboardLayoutSlice.ts b/frontend/src/shared/state/dashboardLayoutSlice.ts
index bbc41acf..7addc518 100644
--- a/frontend/src/shared/state/dashboardLayoutSlice.ts
+++ b/frontend/src/shared/state/dashboardLayoutSlice.ts
@@ -806,6 +806,8 @@ const dashboardLayoutSlice = createSlice({
       }>
     ) {
       const { sessionId, x, y, width, height, expandedSessionIds, exact } = action.payload;
+      // A card keyed "undefined" persists, survives every reload, and threw inside the search palette on each render (a probe once dispatched the wrong key); the bad state is unwritable here.
+      if (typeof sessionId !== 'string' || !sessionId) return;
       const pos = exact ? { x, y } : findOpenSpotNear(x, y, collectOccupiedRects(state, expandedSessionIds), width, height);
       state.cards[sessionId] = {
         session_id: sessionId,
diff --git a/frontend/src/shared/state/placeCardRefusesNoSession.test.ts b/frontend/src/shared/state/placeCardRefusesNoSession.test.ts
new file mode 100644
index 00000000..1636862d
--- /dev/null
+++ b/frontend/src/shared/state/placeCardRefusesNoSession.test.ts
@@ -0,0 +1,17 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import dashboardLayoutReducer, { placeCard } from './dashboardLayoutSlice';
+
+// A drill dispatched placeCard without a sessionId and the reducer wrote cards["undefined"], which persisted and made the
+// search palette throw on every render until the file was edited by hand. The bad state is unrepresentable now.
+test('placeCard without a session id writes nothing', () => {
+  const before = dashboardLayoutReducer(undefined, { type: 'init' });
+  const after = dashboardLayoutReducer(before, placeCard({ x: 1, y: 2, width: 100, height: 100 } as unknown as Parameters<typeof placeCard>[0]));
+  assert.deepEqual(Object.keys(after.cards), Object.keys(before.cards));
+  assert.ok(!('undefined' in after.cards));
+});
+
+test('placeCard with a session id still places', () => {
+  const after = dashboardLayoutReducer(undefined, placeCard({ sessionId: 's1', x: 1, y: 2, width: 100, height: 100, exact: true }));
+  assert.equal(after.cards.s1.x, 1);
+});