Native Builder: Define Snapshotter protocol

Sources/ContainerClient/Archiver.swift

@@ -20,12 +20,25 @@ import Foundation
 
 public final class Archiver: Sendable {
     public struct ArchiveEntryInfo: Sendable {
-        let pathOnHost: URL
-        let pathInArchive: URL
+        public let pathOnHost: URL
+        public let pathInArchive: URL
 
-        public init(pathOnHost: URL, pathInArchive: URL) {
+        public let owner: UInt32?
+        public let group: UInt32?
+        public let permissions: UInt16?
+
+        public init(
+            pathOnHost: URL,
+            pathInArchive: URL,
+            owner: UInt32? = nil,
+            group: UInt32? = nil,
+            permissions: UInt16? = nil
+        ) {
             self.pathOnHost = pathOnHost
             self.pathInArchive = pathInArchive
+            self.owner = owner
+            self.group = group
+            self.permissions = permissions
         }
     }
 
@@ -246,6 +259,21 @@ public final class Archiver: Sendable {
             entry.modificationDate = modificationDate
         }
 
+        // Apply explicit overrides from ArchiveEntryInfo when provided
+        if let overrideOwner = entryInfo.owner {
+            entry.owner = overrideOwner
+        }
+        if let overrideGroup = entryInfo.group {
+            entry.group = overrideGroup
+        }
+        if let overridePerm = entryInfo.permissions {
+            #if os(macOS)
+            entry.permissions = overridePerm
+            #else
+            entry.permissions = UInt32(overridePerm)
+            #endif
+        }
+
         let pathTrimmed = Self._trimPathPrefix(entryInfo.pathInArchive.relativePath, pathPrefix: pathPrefix)
         entry.path = pathTrimmed
         return entry

Sources/NativeBuilder/ContainerBuildDemo/Demo.swift

@@ -21,12 +21,44 @@ import ContainerBuildReporting
 import ContainerBuildSnapshotter
 import Foundation
 
+public actor DummySnapshotter: Snapshotter {
+    public init() {}
+
+    public func prepare(_ snapshot: Snapshot) async throws -> Snapshot {
+        if let mount = snapshot.state.mountpoint {
+            var isDir: ObjCBool = false
+            if !FileManager.default.fileExists(atPath: mount.path, isDirectory: &isDir) {
+                try FileManager.default.createDirectory(at: mount, withIntermediateDirectories: true)
+            }
+        }
+        return snapshot
+    }
+
+    public func commit(_ snapshot: Snapshot) async throws -> Snapshot {
+        // Produce a minimal committed snapshot; layer fields are optional
+        Snapshot(
+            id: snapshot.id,
+            digest: snapshot.digest,
+            size: snapshot.size,
+            parent: snapshot.parent,
+            createdAt: snapshot.createdAt,
+            state: .committed()
+        )
+    }
+
+    public func remove(_ snapshot: Snapshot) async throws {
+        if let mount = snapshot.state.mountpoint {
+            try? FileManager.default.removeItem(at: mount)
+        }
+    }
+}
+
 /// A simple demonstration of the build execution system.
 public struct Demo {
     public static func runDemo() async throws {
         // Set up the build environment first
-        let snapshotter = MemorySnapshotter()
-        let cache = MemoryBuildCache()
+        let snapshotter = DummySnapshotter()
+        let cache = NoOpBuildCache()
         let reporter = Reporter()
 
         // Create a build graph with parallel operations, passing the reporter