selftest: add on-disk SelfTestReport log; report PASS/FAIL details from steps

HellionChat/SelfTests/GlobalStyleScopeAllocStep.cs

@@ -45,16 +45,20 @@ internal sealed class GlobalStyleScopeAllocStep : ISelfTestStep
         GlobalStyleScope.Push(theme, registry, opacity).Dispose();
         var delta = GC.GetAllocatedBytesForCurrentThread() - before;
 
-        if (delta > AllocBudgetBytes)
-        {
-            ImGui.Text(
-                $"GlobalStyleScope.Push allocated {delta} bytes/cycle "
-                    + $"(budget {AllocBudgetBytes}) — StackHandle is not GC-free."
-            );
-            return SelfTestStepResult.Fail;
-        }
-
-        return SelfTestStepResult.Pass;
+        // Report the measured figure on BOTH outcomes (Flo's request: don't just
+        // show Pass) — the byte delta is the whole point of the GC-reserve probe.
+        var ok = delta <= AllocBudgetBytes;
+        var status = ok ? "PASS" : "FAIL";
+        SelfTestReport.Append(
+            Name,
+            status,
+            new[] { $"Push/Dispose allocated {delta} bytes/cycle (budget {AllocBudgetBytes})" }
+        );
+        ImGui.Text(
+            $"GlobalStyleScope.Push allocated {delta} bytes/cycle "
+                + $"(budget {AllocBudgetBytes}) — {status}."
+        );
+        return ok ? SelfTestStepResult.Pass : SelfTestStepResult.Fail;
     }
 
     public void CleanUp() { }

HellionChat/SelfTests/SelfTestReport.cs

@@ -0,0 +1,39 @@
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.IO;
+using System.Text;
+
+namespace HellionChat.SelfTests;
+
+// Shared report sink so manual self-test steps leave a readable trace on disk,
+// not just a green Pass that flashes by for a single frame. Each call appends a
+// timestamped block to selftest-report.log in the plugin ConfigDirectory; the
+// human reads the tail after running the self-test runner. Same idea as the B5
+// perf-baseline.json (durable, copy-pasteable output) but as one shared append
+// log so a full run leaves every reporting step's findings in one place.
+// Append (not atomic tmp+move) is fine: the runner is single-threaded on the
+// draw thread and a torn trailing line on a crash is acceptable for a debug log.
+internal static class SelfTestReport
+{
+    internal static string Append(string stepName, string status, IReadOnlyList<string> details)
+    {
+        var path = Path.Join(Plugin.Interface.ConfigDirectory.FullName, "selftest-report.log");
+
+        var stamp = DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss", CultureInfo.InvariantCulture);
+        var sb = new StringBuilder();
+        sb.Append("=== ")
+            .Append(stamp)
+            .Append(" | ")
+            .Append(stepName)
+            .Append(" | ")
+            .Append(status)
+            .Append(" ===\n");
+        foreach (var line in details)
+            sb.Append("  ").Append(line).Append('\n');
+        sb.Append('\n');
+
+        File.AppendAllText(path, sb.ToString());
+        return path;
+    }
+}