1 files changed, 141 insertions, 0 deletions
diff --git a/src/Agent.Windows/Recovery/TransactionalFileEditor.cs b/src/Agent.Windows/Recovery/TransactionalFileEditor.cs
new file mode 100644
index 0000000..52963a0
--- /dev/null
+++ b/src/Agent.Windows/Recovery/TransactionalFileEditor.cs
@@ -0,0 +1,141 @@
+using System.Security.Cryptography;
+using System.Text;
+using Agent.Windows.Security;
+
+namespace Agent.Windows.Recovery;
+
+public sealed class TransactionalFileEditor(TaskResourceJournal journal, string backupRoot, long memoryBackupLimitBytes = 16 * 1024 * 1024)
+{
+    public FileEditTransaction Replace(string path, string content, string? expectedSha256 = null) => Replace(path, Encoding.UTF8.GetBytes(content), expectedSha256);
+
+    public FileEditTransaction Replace(string path, ReadOnlySpan<byte> content, string? expectedSha256 = null)
+    {
+        string canonical = CanonicalPath.Resolve(path, requireExisting: false);
+        bool existed = File.Exists(canonical);
+        byte[]? original = existed ? File.ReadAllBytes(canonical) : null;
+        string originalHash = original is null ? string.Empty : Convert.ToHexString(SHA256.HashData(original));
+        if (expectedSha256 is not null && !originalHash.Equals(NormalizeHash(expectedSha256), StringComparison.Ordinal))
+            throw new SandboxPolicyException("file.concurrent_change", "File hash does not match expected_sha256.");
+
+        string backupPath = string.Empty;
+        string inline = string.Empty;
+        if (original is not null && original.LongLength > memoryBackupLimitBytes)
+        {
+            string directory = System.IO.Path.Combine(backupRoot, journal.TaskId.ToString("N"));
+            Directory.CreateDirectory(directory);
+            backupPath = System.IO.Path.Combine(directory, Guid.NewGuid().ToString("N") + ".backup");
+            File.WriteAllBytes(backupPath, original);
+        }
+        else if (original is not null) inline = Convert.ToBase64String(original);
+
+        string temporary = canonical + ".agent-mcp-" + Guid.NewGuid().ToString("N") + ".tmp";
+        var data = new Dictionary<string, string>
+        {
+            ["existed"] = existed.ToString(), ["original_sha256"] = originalHash, ["original_base64"] = inline,
+            ["backup_path"] = backupPath, ["temporary_path"] = temporary
+        };
+        Guid entryId = journal.Prepare("file.replace", canonical, data);
+        File.WriteAllBytes(temporary, content);
+        string replacementHash = Convert.ToHexString(SHA256.HashData(content));
+        File.Move(temporary, canonical, overwrite: true);
+        journal.MarkApplied(entryId, new Dictionary<string, string> { ["replacement_sha256"] = replacementHash });
+        return new(journal, entryId, canonical, originalHash, replacementHash, backupPath, inline, existed);
+    }
+
+    public FileDeleteTransaction Delete(string path, string? expectedSha256 = null)
+    {
+        string canonical = CanonicalPath.Resolve(path);
+        byte[] original = File.ReadAllBytes(canonical);
+        string originalHash = Convert.ToHexString(SHA256.HashData(original));
+        if (expectedSha256 is not null && !originalHash.Equals(NormalizeHash(expectedSha256), StringComparison.Ordinal))
+            throw new SandboxPolicyException("file.concurrent_change", "File hash does not match expected_sha256.");
+        string backupPath = string.Empty;
+        string inline = string.Empty;
+        if (original.LongLength > memoryBackupLimitBytes)
+        {
+            string directory = System.IO.Path.Combine(backupRoot, journal.TaskId.ToString("N"));
+            Directory.CreateDirectory(directory);
+            backupPath = System.IO.Path.Combine(directory, Guid.NewGuid().ToString("N") + ".backup");
+            File.WriteAllBytes(backupPath, original);
+        }
+        else inline = Convert.ToBase64String(original);
+        Guid entryId = journal.Prepare("file.delete", canonical, new Dictionary<string, string>
+        {
+            ["original_sha256"] = originalHash, ["original_base64"] = inline, ["backup_path"] = backupPath
+        });
+        File.Delete(canonical);
+        journal.MarkApplied(entryId);
+        return new(journal, entryId, canonical, originalHash, backupPath, inline);
+    }
+
+    private static string NormalizeHash(string hash) => hash.Replace("-", string.Empty, StringComparison.Ordinal).Trim().ToUpperInvariant();
+}
+
+public sealed class FileDeleteTransaction(TaskResourceJournal journal, Guid entryId, string path, string originalHash, string backupPath, string originalBase64)
+{
+    private bool _finished;
+    public void Commit() { if (_finished) return; Cleanup(); journal.MarkCleaned(entryId); _finished = true; }
+    public void Rollback()
+    {
+        if (_finished) return;
+        if (File.Exists(path)) throw new InvalidOperationException("Rollback refused because the deleted path was recreated.");
+        byte[] original = backupPath.Length > 0 ? File.ReadAllBytes(backupPath) : Convert.FromBase64String(originalBase64);
+        if (!Convert.ToHexString(SHA256.HashData(original)).Equals(originalHash, StringComparison.Ordinal)) throw new InvalidDataException("Delete backup hash verification failed.");
+        File.WriteAllBytes(path, original);
+        Cleanup(); journal.MarkCleaned(entryId); _finished = true;
+    }
+    private void Cleanup()
+    {
+        if (backupPath.Length == 0) return;
+        File.Delete(backupPath);
+        string? parent = System.IO.Path.GetDirectoryName(backupPath);
+        if (parent is not null && Directory.Exists(parent) && !Directory.EnumerateFileSystemEntries(parent).Any()) Directory.Delete(parent);
+    }
+}
+
+public sealed class FileEditTransaction(
+    TaskResourceJournal journal, Guid entryId, string path, string originalHash, string replacementHash,
+    string backupPath, string originalBase64, bool originallyExisted)
+{
+    private bool _finished;
+
+    public void Commit()
+    {
+        if (_finished) return;
+        DeleteBackup();
+        journal.MarkCleaned(entryId);
+        _finished = true;
+    }
+
+    public void Rollback()
+    {
+        if (_finished) return;
+        if (!File.Exists(path) || !Hash(path).Equals(replacementHash, StringComparison.Ordinal))
+            throw new InvalidOperationException("Rollback refused because the replacement file changed after the transaction.");
+        if (originallyExisted)
+        {
+            byte[] original = backupPath.Length > 0 ? File.ReadAllBytes(backupPath) : Convert.FromBase64String(originalBase64);
+            if (!Convert.ToHexString(SHA256.HashData(original)).Equals(originalHash, StringComparison.Ordinal)) throw new InvalidDataException("Backup hash verification failed.");
+            string temporary = path + ".rollback-" + Guid.NewGuid().ToString("N") + ".tmp";
+            File.WriteAllBytes(temporary, original);
+            File.Move(temporary, path, overwrite: true);
+        }
+        else File.Delete(path);
+        DeleteBackup();
+        journal.MarkCleaned(entryId);
+        _finished = true;
+    }
+
+    private void DeleteBackup()
+    {
+        if (backupPath.Length == 0) return;
+        File.Delete(backupPath);
+        string? parent = System.IO.Path.GetDirectoryName(backupPath);
+        if (parent is not null && Directory.Exists(parent) && !Directory.EnumerateFileSystemEntries(parent).Any()) Directory.Delete(parent);
+    }
+    private static string Hash(string target)
+    {
+        using FileStream stream = File.OpenRead(target);
+        return Convert.ToHexString(SHA256.HashData(stream));
+    }
+}