diff --git a/src/main/runtime/rpc/worktree-catalog-snapshot.test.ts b/src/main/runtime/rpc/worktree-catalog-snapshot.test.ts
index 70178aa48db..4f52319e523 100644
--- a/src/main/runtime/rpc/worktree-catalog-snapshot.test.ts
+++ b/src/main/runtime/rpc/worktree-catalog-snapshot.test.ts
@@ -63,6 +63,18 @@ describe('resolveWorktreeCatalogSnapshot', () => {
     expect(resolveWorktreeCatalogSnapshot(result(1), null).snapshotId).toBe(warm)
   })
 
+  it('isolates the memo from mutation of a previously resolved catalog', () => {
+    const mutable = result(1)
+    const first = resolveWorktreeCatalogSnapshot(mutable, null)
+
+    mutable.totalCount = 2
+    const changed = resolveWorktreeCatalogSnapshot(mutable, first.snapshotId)
+
+    expect(changed).toMatchObject({ totalCount: 2 })
+    expect(changed).not.toHaveProperty('unchanged')
+    expect(changed.snapshotId).not.toBe(first.snapshotId)
+  })
+
   it('produces ids within the request schema bound', () => {
     const { snapshotId } = resolveWorktreeCatalogSnapshot(result(1), null)
     expect(snapshotId.length).toBeGreaterThan(0)
diff --git a/src/main/runtime/rpc/worktree-catalog-snapshot.ts b/src/main/runtime/rpc/worktree-catalog-snapshot.ts
index 9514266a963..ca5fc944879 100644
--- a/src/main/runtime/rpc/worktree-catalog-snapshot.ts
+++ b/src/main/runtime/rpc/worktree-catalog-snapshot.ts
@@ -24,11 +24,13 @@ function worktreeCatalogSnapshotId(result: RuntimeWorktreePsResult): string {
   if (memoizedId && isDeepStrictEqual(memoizedId.result, result)) {
     return memoizedId.snapshotId
   }
+  const serialized = JSON.stringify(result)
   const snapshotId = createHash('sha256')
-    .update(JSON.stringify(result))
+    .update(serialized)
     .digest('base64url')
     .slice(0, SNAPSHOT_ID_LENGTH)
-  memoizedId = { result, snapshotId }
+  // Why: caller-owned mutation must not let an old id label new catalog content.
+  memoizedId = { result: JSON.parse(serialized) as RuntimeWorktreePsResult, snapshotId }
   return snapshotId
 }