Use file creation time for GetNearestPackages when version is non-SemVer

source/Calamari.Common/Plumbing/FileSystem/CalamariPhysicalFileSystem.cs

@@ -693,6 +693,11 @@ public DateTime GetCreationTime(string filePath)
             return File.GetCreationTime(filePath);
         }
 
+        public DateTime GetLastWriteTime(string filePath)
+        {
+            return File.GetLastWriteTime(filePath);
+        }
+
         public string GetFileName(string filePath)
         {
             return new FileInfo(filePath).Name;

source/Calamari.Common/Plumbing/FileSystem/FileOperations.cs

@@ -15,6 +15,7 @@ public interface IFile
         void Move(string sourceFile, string destination);
         void SetAttributes(string path, FileAttributes normal);
         DateTime GetCreationTime(string filePath);
+        DateTime GetLastWriteTime(string filePath);
         Stream Open(string filePath, FileMode fileMode, FileAccess fileAccess, FileShare none);
     }
 
@@ -73,6 +74,11 @@ public DateTime GetCreationTime(string path)
             return File.GetCreationTime(path);
         }
 
+        public DateTime GetLastWriteTime(string path)
+        {
+            return File.GetLastWriteTime(path);
+        }
+
         public Stream Open(string path, FileMode mode, FileAccess access, FileShare share)
         {
             return File.Open(path, mode, access, share);

source/Calamari.Common/Plumbing/FileSystem/ICalamariFileSystem.cs

@@ -51,6 +51,7 @@ public interface ICalamariFileSystem
         string GetRelativePath(string fromFile, string toFile);
         Stream OpenFileExclusively(string filePath, FileMode fileMode, FileAccess fileAccess);
         DateTime GetCreationTime(string filePath);
+        DateTime GetLastWriteTime(string filePath);
         string GetFileName(string filePath);
         string GetDirectoryName(string directoryPath);
         byte[] ReadAllBytes(string filePath);

source/Calamari.Shared/Integration/Certificates/FileSystem/PackageStore.cs

@@ -71,12 +71,21 @@ public IEnumerable<PackagePhysicalFileMetadata> GetNearestPackages(string packag
         {
             fileSystem.EnsureDirectoryExists(GetPackagesDirectory());
 
-            var zipPackages =
+            var allMatchingPackages =
                 from filePath in PackageFiles(packageId)
                 let zip = PackageMetadata(filePath)
-                where zip != null && string.Equals(zip.PackageId, packageId, StringComparison.OrdinalIgnoreCase) && zip.Version.CompareTo(version) <= 0
-                orderby zip.Version descending
-                select new {zip, filePath};
+                where zip != null && string.Equals(zip.PackageId, packageId, StringComparison.OrdinalIgnoreCase)
+                select new { zip, filePath };
+
+            // For SemVer versions, find packages with version <= target ordered by version descending (closest lower version first).
+            // For non-SemVer versions (Docker tags, build numbers etc.) SemVer comparison is meaningless, so fall back to
+            // ordering by file creation time — the most recently cached package is the best delta candidate.
+            var zipPackages = version.Format == VersionFormat.Semver
+                ? allMatchingPackages
+                    .Where(x => x.zip.Version.CompareTo(version) <= 0)
+                    .OrderByDescending(x => x.zip.Version)
+                : allMatchingPackages
+                    .OrderByDescending(x => fileSystem.GetLastWriteTime(x.filePath));
 
             return
                 from zipPackage in zipPackages.Take(take)

source/Calamari.Tests/Fixtures/Integration/FileSystem/PackageStoreFixture.cs

@@ -8,6 +8,7 @@
 using Calamari.Testing.Helpers;
 using Calamari.Tests.Fixtures.Deployment.Packages;
 using NUnit.Framework;
+using Octopus.Versioning;
 using Octopus.Versioning.Semver;
 
 namespace Calamari.Tests.Fixtures.Integration.FileSystem
@@ -90,6 +91,58 @@ public void IgnoresInvalidFiles()
             }
         }
 
+        [Test]
+        public void NonSemVerVersionsReturnPackagesOrderedByLastWriteTime()
+        {
+            // For non-SemVer tags (Docker tags, build numbers etc.) version comparison is unreliable.
+            // GetNearestPackages should fall back to file last-write time so the most recently
+            // cached package is offered as the delta candidate.
+            //
+            // We bypass PackageBuilder.BuildSamplePackage here because `dotnet pack /p:Version=...`
+            // rejects non-SemVer versions. We also use .zip rather than .nupkg so PackageName.FromFile
+            // does not try to read NuGet metadata from the file content.
+            var v1Path = CreateDummyCachedFile("feature-login-100");
+            var v2Path = CreateDummyCachedFile("main-9999");
+            var v3Path = CreateDummyCachedFile("feature-signup-42");
+
+            // Set deterministic last-write times: v2 is most recent, then v3, then v1.
+            // Using SetLastWriteTimeUtc rather than SetCreationTimeUtc because creation time
+            // is read-only on Linux filesystems.
+            File.SetLastWriteTimeUtc(v1Path, DateTime.UtcNow.AddMinutes(-30));
+            File.SetLastWriteTimeUtc(v3Path, DateTime.UtcNow.AddMinutes(-15));
+            File.SetLastWriteTimeUtc(v2Path, DateTime.UtcNow.AddMinutes(-5));
+
+            using (new TemporaryFile(v1Path))
+            using (new TemporaryFile(v2Path))
+            using (new TemporaryFile(v3Path))
+            {
+                var store = new PackageStore(
+                    CreatePackageExtractor(),
+                    CalamariPhysicalFileSystem.GetPhysicalFileSystem()
+                );
+
+                var target = VersionFactory.TryCreateDockerTag("feature-new-99");
+                var packages = store.GetNearestPackages("Acme.Web", target).ToList();
+
+                // All three are returned (no version filter), ordered by last-write time descending
+                Assert.That(packages.Count, Is.EqualTo(3));
+                Assert.That(packages[0].Version.ToString(), Is.EqualTo("main-9999"));
+                Assert.That(packages[1].Version.ToString(), Is.EqualTo("feature-signup-42"));
+                Assert.That(packages[2].Version.ToString(), Is.EqualTo("feature-login-100"));
+            }
+        }
+
+        private string CreateDummyCachedFile(string version)
+        {
+            var dockerVersion = VersionFactory.TryCreateDockerTag(version)!;
+            // Use .zip rather than .nupkg — .nupkg files trigger NuGet metadata parsing inside
+            // PackageName.FromFile, which would fail on these dummy files. The PackageStore only
+            // reads file metadata (hash, size, last-write time), not the file contents themselves.
+            var destinationPath = Path.Combine(PackagePath, PackageName.ToCachedFileName("Acme.Web", dockerVersion, ".zip"));
+            File.WriteAllText(destinationPath, "dummy content for " + version);
+            return destinationPath;
+        }
+
         private string CreateEmptyFile(string version)
         {
             var destinationPath = Path.Combine(PackagePath, PackageName.ToCachedFileName("Acme.Web", new SemanticVersion(version), ".nupkg"));

source/Calamari.Tests/Fixtures/Integration/FileSystem/TestFile.cs

@@ -15,6 +15,7 @@ public class TestFile : IFile
         public bool Exists(string path) => File.Exists(WithBase(path));
         public byte[] ReadAllBytes(string path) => File.ReadAllBytes(WithBase(path));
         public DateTime GetCreationTime(string filePath) => File.GetCreationTime(WithBase(filePath));
+        public DateTime GetLastWriteTime(string filePath) => File.GetLastWriteTime(WithBase(filePath));
         public Stream Open(string filePath, FileMode fileMode, FileAccess fileAccess, FileShare none) =>
             File.Open(WithBase(filePath), fileMode, fileAccess, none);