diff --git a/apps/desktop/src/store/tool-view.test.ts b/apps/desktop/src/store/tool-view.test.ts
new file mode 100644
index 0000000000..3307f67d72
--- /dev/null
+++ b/apps/desktop/src/store/tool-view.test.ts
@@ -0,0 +1,55 @@
+import { describe, expect, it } from 'vitest'
+
+import { $anyToolDisclosureOpen, $toolDisclosureOpen } from './tool-view'
+
+// Mount and unmount exactly as a rendered tool row does: subscribe (useStore)
+// then unsubscribe (unmount). Everything else — an un-subscribed call — never
+// attaches a listener, so eviction could only be observed through this shape.
+const mountAndUnmount = (atom: { subscribe: (listener: () => void) => () => void }) => {
+  const unsubscribe = atom.subscribe(() => undefined)
+  unsubscribe()
+}
+
+describe('$toolDisclosureOpen cache', () => {
+  it('keeps a stable identity while the row is subscribed', () => {
+    const unsubscribe = $toolDisclosureOpen('tool-entry:stable:0').subscribe(() => undefined)
+
+    try {
+      expect($toolDisclosureOpen('tool-entry:stable:0')).toBe($toolDisclosureOpen('tool-entry:stable:0'))
+    } finally {
+      unsubscribe()
+    }
+  })
+
+  it('releases the cache entry once its row unmounts', () => {
+    const row = $toolDisclosureOpen('tool-entry:evicted:0')
+
+    mountAndUnmount(row)
+
+    // A remount gets a fresh atom: the unmounted row's entry was released
+    // instead of being retained for the window's lifetime (#131121).
+    expect($toolDisclosureOpen('tool-entry:evicted:0')).not.toBe(row)
+  })
+})
+
+describe('$anyToolDisclosureOpen cache', () => {
+  it('keeps a stable identity while the run is subscribed', () => {
+    const ids = ['tool-entry:stable-run:0', 'tool-entry:stable-run:1'] as const
+    const unsubscribe = $anyToolDisclosureOpen(ids).subscribe(() => undefined)
+
+    try {
+      expect($anyToolDisclosureOpen(ids)).toBe($anyToolDisclosureOpen(ids))
+    } finally {
+      unsubscribe()
+    }
+  })
+
+  it('releases the cache entry once its run unmounts', () => {
+    const ids = ['tool-entry:evicted-run:0', 'tool-entry:evicted-run:1'] as const
+    const run = $anyToolDisclosureOpen(ids)
+
+    mountAndUnmount(run)
+
+    expect($anyToolDisclosureOpen(ids)).not.toBe(run)
+  })
+})