⚡ Bolt: Prevent serialisation bottleneck by converting Scanner actors to structs

.jules/bolt.md

@@ -0,0 +1,3 @@
+## 2024-05-18 - Actor Serialization in TaskGroup
+**Learning:** Using an `actor` to manage a `withTaskGroup` where child tasks invoke synchronous, blocking I/O (like `FileManager` operations) directly on the actor inadvertently serializes the tasks on the actor's context, preventing true parallelism and drastically reducing throughput.
+**Action:** Change the `actor` to a `struct` for stateless components interacting with thread-safe dependencies (like `FileManager.default`) to allow tasks to execute concurrently across multiple threads.

Sources/Cacheout/Scanner/CacheScanner.swift

@@ -26,7 +26,14 @@
 
 import Foundation
 
-actor CacheScanner {
+// ⚡ Bolt Optimization:
+// Changed from `actor` to `struct` because this component is stateless and only
+// interacts with thread-safe dependencies (FileManager.default).
+// Using an actor with `withTaskGroup` where child tasks invoke methods on `self`
+// causes the tasks to serialize on the actor's context, destroying parallelism.
+// As a struct, the child tasks can now execute concurrently across threads,
+// significantly improving scan throughput for large file systems.
+struct CacheScanner {
     private let fileManager = FileManager.default
 
     func scanAll(_ categories: [CacheCategory]) async -> [ScanResult] {

Sources/Cacheout/Scanner/NodeModulesScanner.swift

@@ -28,7 +28,13 @@
 
 import Foundation
 
-actor NodeModulesScanner {
+// ⚡ Bolt Optimization:
+// Changed from `actor` to `struct` to prevent task serialization. This component
+// is stateless (only holds thread-safe FileManager.default). In an actor, child
+// tasks in `withTaskGroup` calling methods on `self` are forced to run sequentially.
+// As a struct, the recursive filesystem traversals can run truly concurrently
+// across multiple threads, drastically reducing scan time for deep hierarchies.
+struct NodeModulesScanner {
     private let fileManager = FileManager.default
 
     /// Common directories where developers keep projects