feat(runtime): bridge executor completion to the placement stream

Cutover slice C0 (docs/plans/2026-08-02-placement-cutover.md): the seam
work that lets C3 flip hosts onto a complete receipt stream instead of
growing one mid-cutover. The executor's Released exit now publishes an
acknowledge-only ExecutorCompleted receipt through the one placement
projection stream — registered before observer dispatch, correlated to
the full execution receipt, reaped exactly once on acknowledgement/
discard/session-clear, and counted in the convergence ledger. All three
production placement sinks acknowledge-and-ignore the new kind via early
returns proven behavior-preserving for every existing kind; without them
the first such receipt at cutover would permanently wedge the exact-head
FIFO behind sinks that return false. Provably inert today: the publisher
has no production caller.

Execute's live inputs now derive from Runtime's own owners bound at
GameRuntime construction: UsePositionFromServer is retail's exact
autonomy_level != 2 (CommandInterpreter::UsePositionFromServer
0x006B3B40, startup-only knob), and PlayerDistance uses the live movement
controller's position with a null-safe fallback to the caller struct —
never a fabricated origin. TryPrepareAndSubmitAuthoredPlacement chains
the prepared-collision Setup read through PrepareMover to submission with
zero validation-semantics changes. TryCommitParent and CommitWithdrawal
gain the sibling cancellation flow (residence + ordinary placement
family); TryCommitParent deliberately omits LeaveWorld — retail's
set_parent performs its single gated leave_world (0x00515A90) and a
second would have no counterpart.

Not fully dormant: the two cancellation fixes change Runtime paths
production already calls (today as no-op-adjacent hardening, since
nothing upstream begins a residence yet); everything else is reachable
only by tests. Reviewed: retail-conformance PASS + architecture/
adversarial PASS after one fix round (sink wedge, completion-receipt
lifecycle, null-controller distance). Runtime 921/921; complete Release
solution 10,716 passed / 4 intentional skips.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/AcDream.Runtime.Tests/Entities/RuntimeInitialCreateResidenceStateTests.cs

@@ -2379,6 +2379,82 @@ public sealed class RuntimeInitialCreateResidenceStateTests
             Assert.Single(retained.Continuations).Kind);
     }
 
+    // ---------------------------------------------------------------
+    // C0-4: TryCommitParent/CommitWithdrawal cancellation asymmetries
+    // ---------------------------------------------------------------
+
+    [Fact]
+    public void TryCommitParent_CancelsActiveInitialResidenceAndItsPendingPlacement()
+    {
+        var engine = new PhysicsEngine { DataCache = new PhysicsDataCache() };
+        engine.AddLandblock(
+            Landblock,
+            new TerrainSurface(new byte[81], new float[256]),
+            Array.Empty<CellSurface>(),
+            Array.Empty<PortalPlane>(),
+            worldOffsetX: 0f,
+            worldOffsetY: 0f);
+        using var lifetime = new RuntimeEntityObjectLifetime(engine);
+        Bind(lifetime, 200UL);
+        const uint guid = 0x70004001u;
+        RuntimeEntityRecord canonical = lifetime
+            .RegisterEntityWithInitialResidence(
+                Spawn(guid, 1, setupId: null),
+                isLocalPlayer: false)
+            .Canonical!;
+        Assert.True(lifetime.TryGetInitialCreateResidence(
+            canonical,
+            out RuntimeInitialCreateResidenceLease lease));
+        // Unparented -> the classifier's route performs SetPosition, so
+        // Own() has already begun the lease's own placement operation.
+        // Submit it (a live Place receipt now sits unacknowledged) so
+        // cancellation has an ACTUAL outstanding receipt to discard, not
+        // merely an unpublished AwaitingPreparation operation.
+        Assert.True(lease.Placement.IsValid);
+        AttachDormantBody(lifetime, canonical);
+        RuntimeSetPositionOutcome outcome = lifetime.Physics.SetPosition
+            .SubmitPreparedPlacement(
+                lease.Placement,
+                Prepare(lifetime, lease, RuntimeSetPositionMoverSetup.ResolvedAbsent));
+        Assert.Equal(
+            RuntimeSetPositionStatus.CommittedHostAcknowledgementPending,
+            outcome.Status);
+        Assert.Equal(1, lifetime.Physics.SetPosition.PendingProjectionCount);
+
+        var discards = new List<RuntimePlacementProjectionSnapshot>();
+        using IDisposable subscription = lifetime.Events.SubscribePlacement(
+            new PlacementObserver(delta =>
+            {
+                if (delta.Placement.Kind is RuntimePlacementProjectionKind.Discard)
+                    discards.Add(delta.Placement);
+            }));
+
+        var relation = new ParentAttachmentRelation(
+            ParentGuid: 0x70004100u,
+            ChildGuid: guid,
+            ParentLocation: 1u,
+            PlacementId: 1u,
+            ParentInstanceSequence: 1,
+            ChildPositionSequence: 1);
+        Assert.True(lifetime.TryCommitParent(relation, null, out _));
+
+        Assert.Equal(0, lifetime.CaptureOwnership()
+            .InitialCreateResidenceLeaseCount);
+        Assert.Equal(0, lifetime.Physics.SetPosition.CaptureOwnership()
+            .ActiveOperationCount);
+        // The old Place receipt is REPLACED by a Discard at the same
+        // sequence, not removed outright - still awaiting host ack.
+        Assert.Equal(1, lifetime.Physics.SetPosition.PendingProjectionCount);
+        Assert.False(lifetime.Physics.SetPosition.IsPlacementCurrent(
+            lease.Placement));
+        RuntimePlacementProjectionSnapshot discard = Assert.Single(discards);
+        Assert.Equal(canonical.Key, discard.Token.Entity);
+        Assert.Equal(outcome.Projection.Sequence, discard.Token.Sequence);
+        Assert.True(lifetime.Physics.SetPosition.AcknowledgeProjection(
+            discard.Token));
+        Assert.Equal(0, lifetime.Physics.SetPosition.PendingProjectionCount);
+    }
+
     private static RuntimeSetPositionCommand Prepare(
         RuntimeEntityObjectLifetime lifetime,
         in RuntimeInitialCreateResidenceLease lease,