⚡ Bolt: [performance improvement] Eliminate eager array allocations in computed properties

.jules/bolt.md

@@ -28,3 +28,6 @@
 ## 2025-10-24 - Bulk Disk I/O Parallelization and Thread Pool Starvation
 **Learning:** Both `withTaskGroup` and `Task.detached` schedule their work on Swift's cooperative thread pool, which has only as many threads as the CPU has cores. Running synchronous blocking I/O (like `FileManager.removeItem`) directly inside such tasks ties up cooperative threads — when every thread is parked in a syscall there is nothing left to advance other Swift Concurrency work, which manifests as starvation and (with self-referential `await` chains) outright deadlock. `Task.detached` does not help here: "detached" means unstructured/independent, not "off the cooperative pool."
 **Action:** To parallelize bulk blocking I/O, combine a sliding-window `withThrowingTaskGroup` (e.g., `maxConcurrency` of 8) with a per-item handoff to a GCD queue: wrap the blocking call in `withCheckedThrowingContinuation` and dispatch it via `DispatchQueue.global(qos: .userInitiated).async { ... continuation.resume(...) }`. The cooperative-pool task only `await`s the continuation, so it never holds a thread while the syscall runs.
+## 2025-11-01 - Eager Filtering in Computed Properties
+**Learning:** Calling `.isEmpty` on an eagerly filtered array (e.g., `!selectedResults.isEmpty` where `selectedResults` uses `.filter`) allocates a complete intermediate array just to evaluate a boolean state, causing memory churn in SwiftUI computed properties. Additionally, checking sizes greater than zero (e.g., `selectedNodeModulesSize > 0`) forces full iteration.
+**Action:** Use `.contains(where:)` for boolean checks to short-circuit iteration without allocation, and chain `.lazy.filter` before `.reduce`, `.count`, or `.sorted`.

Sources/Cacheout/ViewModels/CacheoutViewModel.swift

@@ -106,7 +106,7 @@ class CacheoutViewModel: ObservableObject {
     }
 
     var selectedSize: Int64 {
-        selectedResults.reduce(0) { $0 + $1.sizeBytes }
+        scanResults.lazy.filter(\.isSelected).reduce(0) { $0 + $1.sizeBytes }
     }
 
     var formattedSelectedSize: String {
@@ -118,7 +118,7 @@ class CacheoutViewModel: ObservableObject {
     }
 
     var hasResults: Bool { !scanResults.isEmpty || !nodeModulesItems.isEmpty }
-    var hasSelection: Bool { !selectedResults.isEmpty || selectedNodeModulesSize > 0 }
+    var hasSelection: Bool { scanResults.contains(where: \.isSelected) || nodeModulesItems.contains(where: \.isSelected) }
 
     // MARK: - Node Modules computed properties
 

Sources/Cacheout/Views/MenuBarView.swift

@@ -154,7 +154,7 @@ struct MenuBarView: View {
             Spacer()
             statPill(
                 label: "Categories",
-                value: "\(viewModel.scanResults.filter { !$0.isEmpty }.count)",
+                value: "\(viewModel.scanResults.lazy.filter { !$0.isEmpty }.count)",
                 color: .blue
             )
         }
@@ -178,7 +178,7 @@ struct MenuBarView: View {
 
     private var topCategories: some View {
         let top = viewModel.scanResults
-            .filter { !$0.isEmpty }
+            .lazy.filter { !$0.isEmpty }
             .sorted { $0.sizeBytes > $1.sizeBytes }
             .prefix(5)