feat(progression): read surface and change announcements (slice 10a)

reads for the UI: TotalCoins, Lives, IsRunOver, CurrentLevel,
LevelOf/IsOwned/CanAfford, HasCleared. The read half of candidate 01 -
callers get a narrow surface instead of reaching into state.

new domain events LivesChanged / TotalCoinsChanged / SkillSetChanged,
announced by comparing against the last announced value, so an operation
can neither forget to announce nor announce something unchanged.

HandlePlayerDeath now clears the spent attempt - it was still counting
towards TotalCoins after its ledger had been discarded.

republisher and EventBus extended; SkillSetChanged is what SkillManager
will reconcile against instead of the non-atomic call pairs. 65 tests.

progression.tests/ProgressionServiceTests.cs

@@ -21,6 +21,7 @@ public class ProgressionServiceTests
             startingLives: Lives.Of(3));
 
         service.StartPlaythrough(Id);
+        service.DrainEvents();   // setup announces; tests assert about the operation under test
         return service;
     }
 
@@ -84,6 +85,7 @@ public class ProgressionServiceTests
             TwoLevels(), Skills(), Lives.Of(3));
         service.StartPlaythrough(Id);
         service.EnterLevel(First);
+        service.DrainEvents();   // setup announces; tests assert about the operation under test
         return service;
     }
 
@@ -167,4 +169,33 @@ public class ProgressionServiceTests
         Assert.Equal(Second, reloaded.CurrentLevel);
         Assert.Equal(LevelTime.Of(30.0), profileStore.Load().Value!.BestTimeFor(First));
     }
+
+    [Fact]
+    public void Picking_up_a_coin_announces_the_new_total_so_the_hud_never_polls()
+    {
+        // CoinsChanged is emitted from four places today and subscribed by nobody, while Hud rebuilds
+        // three translated strings every frame in _Process. One announcement, one read path.
+        var service = ServiceWithSkills();
+
+        service.RecordCoinsFound(Coins.Of(7));
+
+        var announced = service.DrainEvents().OfType<TotalCoinsChanged>().Single();
+        Assert.Equal(Coins.Of(7), announced.Total);
+        Assert.Equal(Coins.Of(7), service.TotalCoins);
+    }
+
+    [Fact]
+    public void Dying_announces_both_the_remaining_lives_and_the_coins_reverting_to_the_bank()
+    {
+        var service = ServiceWithSkills();
+        service.RecordCoinsFound(Coins.Of(40));
+
+        service.HandlePlayerDeath();
+
+        var events = service.DrainEvents();
+        Assert.Equal(2, events.OfType<LivesChanged>().Single().Remaining.Value);
+        // The attempt is discarded, so the 40 found coins were never banked.
+        Assert.Equal(Coins.Zero, events.OfType<TotalCoinsChanged>().Last().Total);
+        Assert.Equal(Coins.Zero, service.TotalCoins);
+    }
 }