Report a simulator that crashes or closes right after the start

The exit code, read with its signal or NTSTATUS, and the last lines of the
error stream - or of log.txt when it stayed silent. The stream is captured
only while the starter stays to read it.

StarterNG.Tests/SimulatorExitTests.cs

@@ -0,0 +1,65 @@
+using StarterNG.Application;
+using StarterNG.Infrastructure.Adapters;
+using StarterNG.Tests.Fakes;
+
+namespace StarterNG.Tests;
+
+public class SimulatorExitTests
+{
+    private static readonly TimeSpan Session = TimeSpan.FromMinutes(20);
+
+    [Fact]
+    public void A_session_ended_cleanly_is_no_failure()
+    {
+        Assert.False(new SimulatorExit(0, Session, []).Failed);
+    }
+
+    [Fact]
+    public void An_error_code_is_a_failure()
+    {
+        Assert.True(new SimulatorExit(1, Session, []).Failed);
+    }
+
+    [Fact]
+    public void A_window_that_only_flashed_is_a_failure_even_with_a_clean_code()
+    {
+        var exit = new SimulatorExit(0, TimeSpan.FromSeconds(0.2), []);
+
+        Assert.True(exit.Failed);
+        Assert.True(exit.Quick);
+    }
+
+    [Theory]
+    [InlineData(139, "139 (SIGSEGV)")]
+    [InlineData(134, "134 (SIGABRT)")]
+    [InlineData(-1073741819, "0xC0000005 (access violation)")]
+    [InlineData(3, "3")]
+    public void The_code_says_what_killed_it(int code, string described)
+    {
+        Assert.Equal(described, new SimulatorExit(code, Session, []).DescribeCode());
+    }
+
+    [Fact]
+    public void Colour_codes_and_blank_lines_are_dropped_from_the_errors()
+    {
+        var exit = new SimulatorExit(1, Session, ["\u001b[31mBad file: texture\u001b[0m", "", "   "]);
+
+        Assert.Equal(["Bad file: texture"], exit.CleanErrors);
+    }
+
+    [Fact]
+    public async Task A_real_process_leaves_its_exit_code_and_error_stream()
+    {
+        var launcher = new SystemProcessLauncher(new TestInstallation().Log);
+        var (shell, script) = OperatingSystem.IsWindows()
+            ? ("cmd", new[] { "/c", "echo boom 1>&2 & exit 3" })
+            : ("/bin/sh", new[] { "-c", "echo boom >&2; exit 3" });
+
+        var process = launcher.Start(shell, script, null, captureErrors: true, out string? error);
+        Assert.Null(error);
+        await process!.WaitForExitAsync();
+
+        Assert.Equal(3, process.ExitCode);
+        Assert.Equal("boom", Assert.Single(process.ErrorTail).Trim());
+    }
+}