remediate: replace eval cookie writes with safe JS helper + add tests (18.6 Track A)

Both SettingsCookieService and DarkModeCookieService now call window.DeepDrftSettings.setCookie (new Interop/settings/settings.ts) instead of eval. New tests cover SettingsServiceBase parse/format round-trip and the PreferenceAwareStreamingPlayerService invariant (Lossless skips probe; LowData inherits base).

DeepDrftTests/SettingsServiceBaseTests.cs

@@ -0,0 +1,73 @@
+using DeepDrftPublic.Client.Common;
+using DeepDrftPublic.Client.Services;
+
+namespace DeepDrftTests;
+
+/// <summary>
+/// Unit tests for the <see cref="SettingsServiceBase"/> parse/format contract (Phase 18 wave 18.6):
+/// the <c>streamQuality</c> cookie round-trips through <c>FormatStreamQuality</c> → wire string →
+/// <c>ParseStreamQuality</c>, and an absent, empty, or unrecognized cookie value defaults to
+/// <see cref="StreamQuality.LowData"/> (the OQ2 default — a missing preference should never force
+/// lossless unnecessarily on a low-bandwidth listener).
+/// </summary>
+[TestFixture]
+public class SettingsServiceBaseTests
+{
+    // Expose the protected static helpers via a concrete subclass — no other members needed.
+    private sealed class Exposed : SettingsServiceBase
+    {
+        public static StreamQuality Parse(string? v) => ParseStreamQuality(v);
+        public static string Format(StreamQuality q) => FormatStreamQuality(q);
+    }
+
+    // ── round-trip ──
+
+    // LowData serializes and deserializes intact.
+    [Test]
+    public void FormatThenParse_LowData_RoundTrips()
+    {
+        var wire = Exposed.Format(StreamQuality.LowData);
+        Assert.That(Exposed.Parse(wire), Is.EqualTo(StreamQuality.LowData));
+    }
+
+    // Lossless serializes and deserializes intact.
+    [Test]
+    public void FormatThenParse_Lossless_RoundTrips()
+    {
+        var wire = Exposed.Format(StreamQuality.Lossless);
+        Assert.That(Exposed.Parse(wire), Is.EqualTo(StreamQuality.Lossless));
+    }
+
+    // ── default for absent / garbled cookie ──
+
+    // A null cookie (no cookie present) defaults to LowData, not Lossless.
+    [Test]
+    public void Parse_Null_DefaultsToLowData()
+        => Assert.That(Exposed.Parse(null), Is.EqualTo(StreamQuality.LowData));
+
+    // An empty string (cookie present but blank) defaults to LowData.
+    [Test]
+    public void Parse_Empty_DefaultsToLowData()
+        => Assert.That(Exposed.Parse(string.Empty), Is.EqualTo(StreamQuality.LowData));
+
+    // A garbled/unknown name defaults to LowData rather than throwing.
+    // Note: Enum.TryParse accepts numeric strings as valid (e.g. "0" → LowData, "1" → Lossless),
+    // so only non-numeric unrecognized names are tested here.
+    [TestCase("garbage")]
+    [TestCase("lossless_extra")]
+    public void Parse_Unrecognized_DefaultsToLowData(string value)
+        => Assert.That(Exposed.Parse(value), Is.EqualTo(StreamQuality.LowData));
+
+    // Case-insensitive parse: the enum parse is case-insensitive, so wire values survive case drift.
+    [TestCase("lossless")]
+    [TestCase("LOSSLESS")]
+    [TestCase("Lossless")]
+    public void Parse_LosslessCaseVariants_ParseCorrectly(string value)
+        => Assert.That(Exposed.Parse(value), Is.EqualTo(StreamQuality.Lossless));
+
+    [TestCase("lowdata")]
+    [TestCase("LOWDATA")]
+    [TestCase("LowData")]
+    public void Parse_LowDataCaseVariants_ParseCorrectly(string value)
+        => Assert.That(Exposed.Parse(value), Is.EqualTo(StreamQuality.LowData));
+}