Standing fuzz suite and fuzzing log

CLAUDE.md

@@ -31,6 +31,7 @@ System-wide microphone mute/unmute with hotkeys, an always-on-top overlay, sound
 - Run (Windows): `dotnet run --project MicControl`. The app asks for elevation (`highestAvailable`), so run from an elevated terminal or Visual Studio started as administrator.
 - Tests already run on both Windows and Linux. The Windows projects also build on Linux (`EnableWindowsTargeting`).
 - Screenshots for the README and releases (the bundled icon font makes Linux renders match Windows, apart from the About page's system details): set `MICCONTROL_SCREENSHOTS=1` and run the tests; `ScreenshotTests` renders the real windows (headless Skia, sample data, light and dark, greyscale text) into `docs/screenshots`. Re-run after visible UI changes and commit the images.
+- Fuzzing (from the repo root, after a build): `powershell -ExecutionPolicy Bypass -File tools\Fuzz.ps1 [-Scale 5] [-Seed N]` runs the opt-in suite in `MicControl.Tests/Fuzz/` (`MICCONTROL_FUZZ=1`, a new seed each run, printed with any failure) and `tools/FuzzWav.cs` (damaged WAVs through the playback decoder). `docs/fuzzing-report.md` logs each round: what it covered, up to which commit, and what to try next. A new round reads it first and attacks what earlier rounds missed or what changed since; fuzzers that find something graduate into `Fuzz/`.
 - Setup (from the repo root): `installer\build.ps1 [-Version 1.0.0]` publishes the app as one self-contained file and writes `artifacts\MicControl-Setup-<version>.exe`. CI builds it for every push to `master`/`dev` and every PR; a signed `vMAJOR.MINOR.PATCH` tag on `master` drafts a GitHub release, which the developer signs and publishes (see "Branches").
 
 ## Installer and updates

Sources/MicControl.Tests/Fuzz/FuzzRun.cs

@@ -0,0 +1,34 @@
+namespace MicControl.Tests.Fuzz;
+
+/// <summary>
+/// The opt-in fuzz suite: skipped unless MICCONTROL_FUZZ=1 (tools/Fuzz.ps1 sets it). Each run uses a new seed, printed
+/// with every failure; MICCONTROL_FUZZ_SEED repeats a run and MICCONTROL_FUZZ_SCALE multiplies the case counts.
+/// </summary>
+internal static class FuzzRun
+{
+    public static bool Enabled { get; } = Environment.GetEnvironmentVariable("MICCONTROL_FUZZ") == "1";
+
+    public static int Seed { get; } = int.TryParse(Environment.GetEnvironmentVariable("MICCONTROL_FUZZ_SEED"), out var seed)
+        ? seed
+        : System.Random.Shared.Next();
+
+    private static readonly double Factor = double.TryParse(Environment.GetEnvironmentVariable("MICCONTROL_FUZZ_SCALE"),
+        System.Globalization.NumberStyles.Float, System.Globalization.CultureInfo.InvariantCulture, out var factor) && factor > 0 ? factor : 1;
+
+    public static void Require() => Assert.SkipUnless(Enabled, "Set MICCONTROL_FUZZ=1 (or run tools/Fuzz.ps1) to fuzz.");
+
+    /// <summary>A generator for one test: the run's seed mixed with the test's own number, so tests don't share a sequence.</summary>
+    public static Random Random(int salt) => new(unchecked((Seed * 1_000_003) + salt));
+
+    public static int Scale(int cases) => Math.Max(1, (int)(cases * Factor));
+
+    /// <summary>Fails with every distinct problem found, and the seed that repeats the run.</summary>
+    public static void AssertNone(IReadOnlyDictionary<string, string> failures)
+    {
+        if (failures.Count > 0)
+        {
+            Assert.Fail($"Seed {Seed} (set MICCONTROL_FUZZ_SEED={Seed} to repeat this run)\n\n"
+                + string.Join("\n\n", failures.Select(f => f.Key + "\n  " + f.Value)));
+        }
+    }
+}