chore: import upstream snapshot with attribution

Sources/Containerization/Hash.swift

@@ -0,0 +1,40 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025-2026 Apple Inc. and the Containerization project authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//===----------------------------------------------------------------------===//
+
+import ContainerizationError
+import Crypto
+import Foundation
+
+extension Mount {
+    /// A deterministic hash of the mount's source path, used as the virtiofs tag.
+    ///
+    /// Resolves symlinks before hashing so that different paths to the same
+    /// directory produce an identical tag.
+    public var tagHash: String {
+        get throws {
+            try hashFilePath(path: self.source)
+        }
+    }
+}
+
+func hashFilePath(path: String) throws -> String {
+    // Resolve symlinks so different paths to the same directory get the same hash.
+    let resolvedSource = URL(fileURLWithPath: path).resolvingSymlinksInPath().path
+    guard let data = resolvedSource.data(using: .utf8) else {
+        throw ContainerizationError(.invalidArgument, message: "\(path) could not be converted to Data")
+    }
+    return String(SHA256.hash(data: data).encoded.prefix(36))
+}