refactor(net): own live session composition

Extract reset, selection, entered-world, and route construction behind LiveSessionHost while preserving the sole LiveSessionController authority. Retain partial route and subscription cleanup for retry, and replace the embedded ACE-only shortcut with the exact named-retail unsigned skill formula.

Co-authored-by: Codex <codex@openai.com>

tests/AcDream.App.Tests/Net/LiveSessionSubscriptionSetTests.cs

@@ -0,0 +1,60 @@
+using AcDream.App.Net;
+
+namespace AcDream.App.Tests.Net;
+
+public sealed class LiveSessionSubscriptionSetTests
+{
+    [Fact]
+    public void Dispose_RetriesOnlyFailedEdgesUntilTheyConverge()
+    {
+        var order = new List<int>();
+        var subscriptions = new LiveSessionSubscriptionSet();
+        subscriptions.Add(() => order.Add(1));
+        int secondFailures = 1;
+        subscriptions.Add(() =>
+        {
+            order.Add(2);
+            if (secondFailures-- > 0)
+                throw new InvalidOperationException("second failed");
+        });
+        int thirdFailures = 1;
+        subscriptions.Add(() =>
+        {
+            order.Add(3);
+            if (thirdFailures-- > 0)
+                throw new IOException("third failed");
+        });
+
+        AggregateException error = Assert.Throws<AggregateException>(
+            subscriptions.Dispose);
+
+        Assert.Equal([3, 2, 1], order);
+        Assert.Collection(
+            error.InnerExceptions,
+            exception => Assert.IsType<IOException>(exception),
+            exception => Assert.IsType<InvalidOperationException>(exception));
+
+        subscriptions.Dispose();
+        subscriptions.Dispose();
+
+        Assert.Equal([3, 2, 1, 3, 2], order);
+    }
+
+    [Fact]
+    public void Dispose_PersistentFailureNeverReplaysSuccessfulEdges()
+    {
+        var order = new List<int>();
+        var subscriptions = new LiveSessionSubscriptionSet();
+        subscriptions.Add(() => order.Add(1));
+        subscriptions.Add(() =>
+        {
+            order.Add(2);
+            throw new InvalidOperationException("persistent");
+        });
+
+        Assert.Throws<AggregateException>(subscriptions.Dispose);
+        Assert.Throws<AggregateException>(subscriptions.Dispose);
+
+        Assert.Equal([2, 1, 2], order);
+    }
+}