End output lines only at CR, LF and CRLF [patch]

README.md

@@ -394,7 +394,7 @@ Processes output in raw, undelimited chunks as they arrive from the process.
 
 ### `LineOutputHandler`
 
-Inherits from `OutputHandler` and buffers incoming chunks, invoking the delegates once per complete line. Incomplete trailing data is held until the rest of the line arrives.
+Inherits from `OutputHandler` and buffers incoming chunks, invoking the delegates once per complete line. Incomplete trailing data is held until the rest of the line arrives. Lines end at LF, CR or CRLF, the same as `Process.OutputDataReceived` and `StreamReader.ReadLine`; NEL (U+0085), LS (U+2028), PS (U+2029) and form feed stay inside the line, so line-delimited JSON that carries them raw arrives one record per call.
 
 #### Constructor
 

RunCommand.Test/LineOutputHandlerTests.cs

@@ -164,6 +164,47 @@ public void HandleStandardOutputDataShouldSplitOnEveryLineEndingKind()
 		Assert.AreEqual("e", handler.outputBuffer.ToString());
 	}
 
+	[TestMethod]
+	[DataRow('\u2028', DisplayName = "LS")]
+	[DataRow('\u2029', DisplayName = "PS")]
+	[DataRow('\u0085', DisplayName = "NEL")]
+	[DataRow('\f', DisplayName = "FF")]
+	public void HandleStandardOutputDataShouldKeepAnUnusualSeparatorInsideTheLine(char separator)
+	{
+		// Arrange
+		string record = $"{{\"a\":\"x{separator}y\"}}";
+		List<string> lines = [];
+		LineOutputHandler handler = new(onStandardOutput: lines.Add);
+
+		// Act
+		handler.HandleStandardOutputData($"{record}\n{record}\n");
+
+		// Assert
+		string[] expected = [record, record];
+		Assert.AreSequenceEqual(expected, lines);
+	}
+
+	[TestMethod]
+	[DataRow('\u2028', DisplayName = "LS")]
+	[DataRow('\u2029', DisplayName = "PS")]
+	[DataRow('\u0085', DisplayName = "NEL")]
+	[DataRow('\f', DisplayName = "FF")]
+	public void HandleStandardErrorDataShouldKeepAnUnusualSeparatorOnAChunkBoundaryInsideTheLine(char separator)
+	{
+		// Arrange
+		List<string> lines = [];
+		LineOutputHandler handler = new(onStandardError: lines.Add);
+
+		// Act
+		handler.HandleStandardErrorData($"x{separator}");
+		handler.HandleStandardErrorData($"y\nz{separator}");
+		handler.HandleStandardErrorData("\n");
+
+		// Assert
+		string[] expected = [$"x{separator}y", $"z{separator}"];
+		Assert.AreSequenceEqual(expected, lines);
+	}
+
 	[TestMethod]
 	public void CompleteShouldDeliverTheFinalUnterminatedLine()
 	{

RunCommand/LineOutputHandler.cs

@@ -200,9 +200,11 @@ private static void EmitLine(StringBuilder buffer, string data, int start, int e
 	}
 
 	/// <summary>
-	/// Determines whether a character other than CR ends a line, matching the set <c>string.ReplaceLineEndings</c> recognises.
+	/// Determines whether a character other than CR ends a line. Only LF does, matching
+	/// <c>Process.OutputDataReceived</c> and <c>StreamReader.ReadLine</c>: NEL, LS, PS and FF are ordinary characters,
+	/// since tools emit them raw inside JSON strings and a line-delimited record must arrive whole.
 	/// </summary>
 	/// <param name="c">The character to test.</param>
-	/// <returns><see langword="true"/> if <paramref name="c"/> is LF, NEL, LS, PS or FF; otherwise <see langword="false"/>.</returns>
-	private static bool IsLineBreak(char c) => c is '\n' or '\u0085' or '\u2028' or '\u2029' or '\f';
+	/// <returns><see langword="true"/> if <paramref name="c"/> is LF; otherwise <see langword="false"/>.</returns>
+	private static bool IsLineBreak(char c) => c == '\n';
 }