feat(progression): remaining slice 1 value objects

Lives (floors at zero, exhaustion observable), LevelId, SkillId,
PlaythroughId (never self-generates, keeps tests deterministic),
StatName enum, LevelTime rejects NaN/infinity.

14 tests. Arithmetic/comparison members deferred to the slices whose
behaviour needs them rather than added speculatively.

progression.tests/CoinsTests.cs

@@ -14,4 +14,10 @@ public class CoinsTests
         // which is the safe outcome; clamping would silently consume what wasn't there.
         Assert.Equal(Coins.Of(10), remaining);
     }
+
+    [Fact]
+    public void A_negative_quantity_of_coins_cannot_exist()
+    {
+        Assert.Throws<ArgumentOutOfRangeException>(() => Coins.Of(-1));
+    }
 }

progression.tests/LevelIdTests.cs

@@ -0,0 +1,14 @@
+namespace Mr.BrickAdventures.Progression.Tests;
+
+public class LevelIdTests
+{
+    [Theory]
+    [InlineData("")]
+    [InlineData("   ")]
+    public void A_blank_id_is_not_a_level(string value)
+    {
+        // Levels are addressed by a stable authored id, never by position in a list. An unset
+        // field in a .tres would otherwise become a valid id that silently collides with itself.
+        Assert.Throws<ArgumentException>(() => LevelId.Of(value));
+    }
+}

progression.tests/LevelTimeTests.cs

@@ -10,4 +10,14 @@ public class LevelTimeTests
         // files. Rejecting zero makes that unrepresentable rather than merely unlikely.
         Assert.Throws<ArgumentOutOfRangeException>(() => LevelTime.Of(0));
     }
+
+    [Theory]
+    [InlineData(double.NaN)]
+    [InlineData(double.PositiveInfinity)]
+    public void A_time_that_is_not_a_finite_number_is_rejected(double seconds)
+    {
+        // Times are derived from subtracting tick counts, so a stale or unset start time can
+        // produce NaN or infinity rather than a plausible-but-wrong number.
+        Assert.Throws<ArgumentOutOfRangeException>(() => LevelTime.Of(seconds));
+    }
 }

progression.tests/LivesTests.cs

@@ -0,0 +1,21 @@
+namespace Mr.BrickAdventures.Progression.Tests;
+
+public class LivesTests
+{
+    [Fact]
+    public void Losing_the_last_life_exhausts_them()
+    {
+        var remaining = Lives.Of(1).Decrement();
+
+        Assert.Equal(0, remaining.Value);
+        Assert.True(remaining.IsExhausted);
+    }
+
+    [Fact]
+    public void Decrementing_when_already_exhausted_stays_at_zero()
+    {
+        var remaining = Lives.Of(0).Decrement();
+
+        Assert.Equal(0, remaining.Value);
+    }
+}

progression.tests/PlaythroughIdTests.cs

@@ -0,0 +1,13 @@
+namespace Mr.BrickAdventures.Progression.Tests;
+
+public class PlaythroughIdTests
+{
+    [Fact]
+    public void The_empty_guid_is_not_a_playthrough()
+    {
+        // Ids arrive from an adapter, never from Guid.NewGuid() inside the domain — otherwise every
+        // test touching identity would be non-deterministic. That makes a default-valued guid a
+        // realistic mistake worth refusing.
+        Assert.Throws<ArgumentException>(() => PlaythroughId.Of(Guid.Empty));
+    }
+}

progression.tests/SkillIdTests.cs

@@ -0,0 +1,20 @@
+namespace Mr.BrickAdventures.Progression.Tests;
+
+public class SkillIdTests
+{
+    [Theory]
+    [InlineData("")]
+    [InlineData("   ")]
+    public void A_blank_id_is_not_a_skill(string value)
+    {
+        Assert.Throws<ArgumentException>(() => SkillId.Of(value));
+    }
+
+    [Fact]
+    public void Ids_with_the_same_text_are_the_same_skill()
+    {
+        // Owned skills are held in a dictionary keyed by id, so value equality is what makes the
+        // type usable at all rather than a convenience.
+        Assert.Equal(SkillId.Of("brick_throw"), SkillId.Of("brick_throw"));
+    }
+}