feat(runtime): define borrowed views commands and ordered events

Establish the J1 presentation-independent contract with instance-scoped clocks and generations, immutable borrowed views, typed generation-gated commands, normalized ordered diagnostics, and teardown acknowledgements. Route graphical startup plus press-time selection, movement, and combat through focused App adapters over the exact existing owners without adding a queue or mirrored world.

Validated by the Release solution build, 13 Runtime tests, 3,838 App tests with three existing skips, and the complete 8,424-test Release suite with five existing skips.

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

src/AcDream.Runtime/RuntimeGeneration.cs

@@ -0,0 +1,62 @@
+namespace AcDream.Runtime;
+
+/// <summary>
+/// Identifies one exact client-session generation. Default is the
+/// pre-session generation and remains a valid compare token.
+/// </summary>
+public readonly record struct RuntimeGenerationToken(ulong Value)
+{
+    public static RuntimeGenerationToken Initial => default;
+
+    public RuntimeGenerationToken Next() => new(checked(Value + 1UL));
+
+    public override string ToString() => Value.ToString(
+        System.Globalization.CultureInfo.InvariantCulture);
+}
+
+public enum RuntimeLifecycleState
+{
+    Constructed,
+    Stopped,
+    Starting,
+    InWorld,
+    Stopping,
+    Faulted,
+    Disposed,
+}
+
+public readonly record struct RuntimeLifecycleSnapshot(
+    RuntimeGenerationToken Generation,
+    RuntimeLifecycleState State,
+    uint PlayerGuid,
+    bool HasTransport);
+
+[Flags]
+public enum RuntimeTeardownStage
+{
+    None = 0,
+    CommandsInert = 1 << 0,
+    InboundDetached = 1 << 1,
+    TransportDisposed = 1 << 2,
+    HostReset = 1 << 3,
+    Complete = CommandsInert | InboundDetached | TransportDisposed | HostReset,
+}
+
+/// <summary>
+/// A generation-scoped acknowledgement. A caller may retry only the missing
+/// suffix; completed teardown stages never replay.
+/// </summary>
+public readonly record struct RuntimeTeardownAcknowledgement(
+    RuntimeGenerationToken RetiredGeneration,
+    RuntimeGenerationToken CurrentGeneration,
+    RuntimeCommandStatus Status,
+    RuntimeTeardownStage CompletedStages,
+    Exception? Error = null)
+{
+    public bool IsComplete =>
+        Status == RuntimeCommandStatus.Accepted
+        &&
+        (CompletedStages & RuntimeTeardownStage.Complete)
+        == RuntimeTeardownStage.Complete
+        && Error is null;
+}