refactor: extract TrackFileStats shared stat/hash helper

Music.xcodeproj/project.pbxproj

@@ -443,7 +443,7 @@
 				"CODE_SIGN_IDENTITY[sdk=macosx*]" = "Apple Development";
 				CODE_SIGN_STYLE = Automatic;
 				COMBINE_HIDPI_IMAGES = YES;
-				CURRENT_PROJECT_VERSION = 21;
+				CURRENT_PROJECT_VERSION = 24;
 				DEAD_CODE_STRIPPING = YES;
 				DEVELOPMENT_TEAM = 526E96RFNP;
 				ENABLE_APP_SANDBOX = YES;
@@ -488,7 +488,7 @@
 				"CODE_SIGN_IDENTITY[sdk=macosx*]" = "Apple Development";
 				CODE_SIGN_STYLE = Automatic;
 				COMBINE_HIDPI_IMAGES = YES;
-				CURRENT_PROJECT_VERSION = 21;
+				CURRENT_PROJECT_VERSION = 24;
 				DEAD_CODE_STRIPPING = YES;
 				DEVELOPMENT_TEAM = 526E96RFNP;
 				ENABLE_APP_SANDBOX = YES;

Music/Services/ScannerService.swift

@@ -159,9 +159,7 @@ final class ScannerService {
                 }
             }
 
-            let attrs = try FileManager.default.attributesOfItem(atPath: url.path)
-            let fileSize = attrs[.size] as? Int64 ?? 0
-            let modDate = attrs[.modificationDate] as? Date ?? Date()
+            let stats = try TrackFileStats.compute(for: url)
 
             return Track(
                 fileURL: url.absoluteString,
@@ -179,13 +177,13 @@ final class ScannerService {
                 fileFormat: url.pathExtension.lowercased(),
                 bitrate: bitrate,
                 sampleRate: sampleRate,
-                fileSize: fileSize,
+                fileSize: stats.fileSize,
                 playCount: 0,
                 lastPlayedAt: nil,
                 rating: 0,
                 dateAdded: Date(),
-                dateModified: modDate,
-                fileHash: Track.computeHash(fileSize: fileSize, modificationDate: modDate)
+                dateModified: stats.dateModified,
+                fileHash: stats.fileHash
             )
         } catch {
             print("Failed to extract metadata from \(url.lastPathComponent): \(error)")

Music/Services/TrackFileStats.swift

@@ -0,0 +1,22 @@
+import Foundation
+
+// Reads a file's size + modification date and derives the library fileHash.
+// Centralizes the computation so ScannerService (import) and TrackEditService
+// (post-writeback refresh) can never drift. Hash uses Track.computeHash so the
+// format stays identical to import-time hashes.
+nonisolated struct TrackFileStats: Sendable {
+    let fileSize: Int64
+    let dateModified: Date
+    let fileHash: String
+
+    static func compute(for url: URL) throws -> TrackFileStats {
+        let attrs = try FileManager.default.attributesOfItem(atPath: url.path)
+        let fileSize = attrs[.size] as? Int64 ?? 0
+        let modDate = attrs[.modificationDate] as? Date ?? Date()
+        return TrackFileStats(
+            fileSize: fileSize,
+            dateModified: modDate,
+            fileHash: Track.computeHash(fileSize: fileSize, modificationDate: modDate)
+        )
+    }
+}

MusicTests/TrackFileStatsTests.swift

@@ -0,0 +1,26 @@
+import Foundation
+import Testing
+@testable import Music
+
+// Verifies the shared file-stat helper reads size/mod-date from disk and
+// produces a fileHash identical to Track.computeHash (the existing canonical formula).
+struct TrackFileStatsTests {
+    @Test func compute_matchesTrackComputeHash() throws {
+        // Step 1: write a temp file with known bytes.
+        let url = URL(fileURLWithPath: NSTemporaryDirectory())
+            .appendingPathComponent(UUID().uuidString + ".bin")
+        try Data(repeating: 0xAB, count: 1234).write(to: url)
+        defer { try? FileManager.default.removeItem(at: url) }
+
+        // Step 2: compute stats via the helper.
+        let stats = try TrackFileStats.compute(for: url)
+
+        // Step 3: independently read attrs and assert the helper agrees.
+        let attrs = try FileManager.default.attributesOfItem(atPath: url.path)
+        let size = attrs[.size] as? Int64 ?? -1
+        let mod = attrs[.modificationDate] as? Date ?? Date.distantPast
+        #expect(stats.fileSize == size)
+        #expect(stats.dateModified == mod)
+        #expect(stats.fileHash == Track.computeHash(fileSize: size, modificationDate: mod))
+    }
+}