Add SaveToFileAsync(fs) convenience overload to WavFile and AiffFile

TDD: Added tests first, then implemented the missing overload that
saves back to SourcePath. This aligns WavFile and AiffFile with
FlacFile and other format types that have the same pattern.

The overload returns failure with 'source path' message when the
file was parsed from bytes rather than read from disk.

Author: decriptor

src/TagLibSharp2/Aiff/AiffFile.cs

@@ -388,6 +388,27 @@ public Task<FileWriteResult> SaveToFileAsync (
 		var data = Render ();
 		return AtomicFileWriter.WriteAsync (path, data.Memory, fileSystem, cancellationToken);
 	}
+
+	/// <summary>
+	/// Saves the AIFF file back to its source path asynchronously.
+	/// </summary>
+	/// <remarks>
+	/// This convenience method saves the file back to the path it was read from.
+	/// Requires that the file was read using <see cref="ReadFromFile"/> or
+	/// <see cref="ReadFromFileAsync"/>.
+	/// </remarks>
+	/// <param name="fileSystem">Optional file system abstraction.</param>
+	/// <param name="cancellationToken">Cancellation token.</param>
+	/// <returns>The write result.</returns>
+	public Task<FileWriteResult> SaveToFileAsync (
+		IFileSystem? fileSystem = null,
+		CancellationToken cancellationToken = default)
+	{
+		if (string.IsNullOrEmpty (SourcePath))
+			return Task.FromResult (FileWriteResult.Failure ("No source path available. File was not read from disk."));
+
+		return SaveToFileAsync (SourcePath!, fileSystem, cancellationToken);
+	}
 }
 
 /// <summary>

src/TagLibSharp2/Riff/WavFile.cs

@@ -386,6 +386,27 @@ public Task<FileWriteResult> SaveToFileAsync (
 		var data = Render ();
 		return AtomicFileWriter.WriteAsync (path, data.Memory, fileSystem, cancellationToken);
 	}
+
+	/// <summary>
+	/// Saves the WAV file back to its source path asynchronously.
+	/// </summary>
+	/// <remarks>
+	/// This convenience method saves the file back to the path it was read from.
+	/// Requires that the file was read using <see cref="ReadFromFile"/> or
+	/// <see cref="ReadFromFileAsync"/>.
+	/// </remarks>
+	/// <param name="fileSystem">Optional file system abstraction.</param>
+	/// <param name="cancellationToken">Cancellation token.</param>
+	/// <returns>The write result.</returns>
+	public Task<FileWriteResult> SaveToFileAsync (
+		IFileSystem? fileSystem = null,
+		CancellationToken cancellationToken = default)
+	{
+		if (string.IsNullOrEmpty (SourcePath))
+			return Task.FromResult (FileWriteResult.Failure ("No source path available. File was not read from disk."));
+
+		return SaveToFileAsync (SourcePath!, fileSystem, cancellationToken);
+	}
 }
 
 /// <summary>

tests/TagLibSharp2.Tests/Aiff/AiffFileAsyncTests.cs

@@ -93,4 +93,37 @@ public async Task SaveToFileAsync_PreservesStructure ()
 		Assert.AreEqual ("Test", verifyResult.File!.Tag?.Title);
 		Assert.AreEqual ("Artist", verifyResult.File.Tag?.Artist);
 	}
+
+	[TestMethod]
+	public async Task SaveToFileAsync_BackToSource_Succeeds ()
+	{
+		var mockFs = new MockFileSystem ();
+		var originalData = TestBuilders.Aiff.CreateMinimal ();
+		mockFs.AddFile ("/test.aiff", originalData);
+
+		var readResult = await AiffFile.ReadFromFileAsync ("/test.aiff", mockFs);
+		var file = readResult.File!;
+		file.Tag = new Id3v2Tag { Title = "Overwritten Title" };
+
+		var saveResult = await file.SaveToFileAsync (mockFs);
+
+		Assert.IsTrue (saveResult.IsSuccess);
+
+		var verifyResult = await AiffFile.ReadFromFileAsync ("/test.aiff", mockFs);
+		Assert.AreEqual ("Overwritten Title", verifyResult.File!.Tag?.Title);
+	}
+
+	[TestMethod]
+	public async Task SaveToFileAsync_NoSourcePath_ReturnsFailure ()
+	{
+		var data = TestBuilders.Aiff.CreateMinimal ();
+		var result = AiffFile.Read (data);
+		var file = result.File!;
+
+		var mockFs = new MockFileSystem ();
+		var saveResult = await file.SaveToFileAsync (mockFs);
+
+		Assert.IsFalse (saveResult.IsSuccess);
+		Assert.IsTrue (saveResult.Error!.Contains ("source path", StringComparison.OrdinalIgnoreCase));
+	}
 }

tests/TagLibSharp2.Tests/Riff/WavFileAsyncTests.cs

@@ -93,4 +93,37 @@ public async Task SaveToFileAsync_PreservesStructure ()
 		Assert.AreEqual ("Test", verifyResult.File!.Id3v2Tag?.Title);
 		Assert.AreEqual ("Artist", verifyResult.File.Id3v2Tag?.Artist);
 	}
+
+	[TestMethod]
+	public async Task SaveToFileAsync_BackToSource_Succeeds ()
+	{
+		var mockFs = new MockFileSystem ();
+		var originalData = TestBuilders.Wav.CreateMinimal ();
+		mockFs.AddFile ("/test.wav", originalData);
+
+		var readResult = await WavFile.ReadFromFileAsync ("/test.wav", mockFs);
+		var file = readResult.File!;
+		file.Id3v2Tag = new Id3v2Tag { Title = "Overwritten Title" };
+
+		var saveResult = await file.SaveToFileAsync (mockFs);
+
+		Assert.IsTrue (saveResult.IsSuccess);
+
+		var verifyResult = await WavFile.ReadFromFileAsync ("/test.wav", mockFs);
+		Assert.AreEqual ("Overwritten Title", verifyResult.File!.Id3v2Tag?.Title);
+	}
+
+	[TestMethod]
+	public async Task SaveToFileAsync_NoSourcePath_ReturnsFailure ()
+	{
+		var data = TestBuilders.Wav.CreateMinimal ();
+		var result = WavFile.Read (data);
+		var file = result.File!;
+
+		var mockFs = new MockFileSystem ();
+		var saveResult = await file.SaveToFileAsync (mockFs);
+
+		Assert.IsFalse (saveResult.IsSuccess);
+		Assert.IsTrue (saveResult.Error!.Contains ("source path", StringComparison.OrdinalIgnoreCase));
+	}
 }