[Fusion] Make FusionArchive generation deterministic (#8994)

Author: tobias-tengler

src/HotChocolate/Fusion-vnext/src/Fusion.Packaging/ArchiveSession.cs

@@ -126,52 +126,48 @@ public void SetMode(FusionArchiveMode mode)
 
     public async Task CommitAsync(CancellationToken cancellationToken)
     {
-        foreach (var file in _files.Values)
+        foreach (var file in _files.Values.OrderBy(f => f.Path, StringComparer.Ordinal))
         {
-#if NET10_0_OR_GREATER
             switch (file.State)
             {
                 case FileState.Created:
-                    await _archive.CreateEntryFromFileAsync(
-                        file.TempPath,
-                        file.Path,
-                        cancellationToken: cancellationToken);
+                    await CreateEntryFromFileAsync(file.TempPath, file.Path, cancellationToken);
                     break;
 
                 case FileState.Replaced:
                     _archive.GetEntry(file.Path)?.Delete();
-                    await _archive.CreateEntryFromFileAsync(
-                        file.TempPath,
-                        file.Path,
-                        cancellationToken);
+                    await CreateEntryFromFileAsync(file.TempPath, file.Path, cancellationToken);
                     break;
 
                 case FileState.Deleted:
                     _archive.GetEntry(file.Path)?.Delete();
                     break;
             }
-#else
-            switch (file.State)
-            {
-                case FileState.Created:
-                    _archive.CreateEntryFromFile(file.TempPath, file.Path);
-                    break;
 
-                case FileState.Replaced:
-                    _archive.GetEntry(file.Path)?.Delete();
-                    _archive.CreateEntryFromFile(file.TempPath, file.Path);
-                    break;
+            file.MarkRead();
+        }
+    }
 
-                case FileState.Deleted:
-                    _archive.GetEntry(file.Path)?.Delete();
-                    break;
-            }
+    /// <summary>
+    /// Creates a ZIP entry from a file with a deterministic timestamp.
+    /// Using a fixed timestamp ensures binary reproducibility of the archive.
+    /// </summary>
+    private async Task CreateEntryFromFileAsync(
+        string sourceFileName,
+        string entryName,
+        CancellationToken cancellationToken)
+    {
+        var entry = _archive.CreateEntry(entryName);
+        // Use a fixed timestamp to ensure deterministic archive output
+        entry.LastWriteTime = new DateTimeOffset(2000, 1, 1, 0, 0, 0, TimeSpan.Zero);
 
-            await Task.CompletedTask;
+        await using var source = File.OpenRead(sourceFileName);
+#if NET10_0_OR_GREATER
+        await using var destination = await entry.OpenAsync(cancellationToken);
+#else
+        await using var destination = entry.Open();
 #endif
-
-            file.MarkRead();
-        }
+        await source.CopyToAsync(destination, cancellationToken);
     }
 
     private static async Task ExtractFileAsync(