fix #270: retry spawn placement until first success (lost-cell recovery analog) + attributed probes

The creation-only spawn placement could no-op or fail during the login
flood (cell id not yet hydrated / streaming collision not resident) with
nothing retrying - monsters created in that window stayed
airborne-flagged forever and their action animations remained refused.
Retail's answer to 'object addressed before its cell exists' is the
CObjectMaint lost-cell list (GotoLostCell): park, re-place when the cell
is available. The UM dispatch path now retries SeedRemoteSpawnPlacement
while the body has never been successfully placed (no contact AND no
stored plane); one success ends the retries.

Probes: [SPAWN-PLACE] logs each placement outcome (guid/cell/ok/
contact/walkable); [UM-ACT]/[MT-FAIL] now carry the owning guid via
MotionInterpreter.DiagnosticGuid (probe-identity-attribution lesson)
plus the body's live contact/walkable flags.

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

src/AcDream.App/Physics/LiveEntityMotionRuntimeController.cs

@@ -45,6 +45,8 @@ internal sealed class LiveEntityMotionRuntimeController
             rm.Sink = new AcDream.Core.Physics.Motion.MotionTableDispatchSink(sequencer);
             rm.Motion.DefaultSink = rm.Sink;
         }
+        // #270 probe identity — strip with the probes.
+        rm.Motion.DiagnosticGuid = serverGuid;
         // #174 (2026-07-05): the RemoveLinkAnimations seam is retail
         // CPhysicsObj::RemoveLinkAnimations 0x0050fe20 — a TAILCALL to
         // CPartArray::HandleEnterWorld 0x00517d70 →

src/AcDream.App/Physics/LiveEntityNetworkUpdateController.cs

@@ -190,6 +190,12 @@ internal sealed class LiveEntityNetworkUpdateController
                   | AcDream.Core.Physics.ObjectInfoState.EdgeSlide
                 : AcDream.Core.Physics.ObjectInfoState.EdgeSlide,
             movingEntityId: entity.Id);
+        if (AcDream.Core.Physics.PhysicsDiagnostics.DumpMotionEnabled)
+        {
+            Console.WriteLine(
+                $"[SPAWN-PLACE] guid={serverGuid:X8} cell=0x{cellId:X8} ok={placement.Ok} "
+                + $"contact={placement.InContact} walkable={placement.OnWalkable}");
+        }
         if (!placement.Ok)
             return; // unplaceable — stays airborne, like a failed retail placement
 
@@ -720,15 +726,24 @@ internal sealed class LiveEntityNetworkUpdateController
                 update.Guid);
             remote.Body.Orientation = entity.Rotation;
             remote.Body.Position = entity.Position;
-            // #270: run the retail spawn placement so the fresh body has
-            // real ground contact BEFORE the funnel below dispatches this
-            // packet's actions — a first-ever-UM attack swing needs
-            // contact_allows_move true to animate.
+        }
+        // #270: run the retail spawn placement so the body has real ground
+        // contact BEFORE the funnel below dispatches this packet's actions —
+        // an attack swing needs contact_allows_move true to animate. Retried
+        // (not creation-only) while the body has never been successfully
+        // placed: creation during the login flood can precede streaming
+        // residency or the entity's cell hydration, and retail's own answer
+        // to "object addressed before its cell exists" is the
+        // CObjectMaint lost-cell list — park it, re-place when the cell is
+        // available. The no-contact-and-no-plane predicate is exactly
+        // "never placed"; one success ends the retries.
+        if (!remote.Body.InContact && !remote.Body.ContactPlaneValid)
+        {
             SeedRemoteSpawnPlacement(
                 remote,
                 update.Guid,
                 entity,
-                entity.Position,
+                remote.Body.Position,
                 // Interior live entities carry ParentCellId; outdoor live
                 // entities carry the outdoor landcell in EffectCellId (see
                 // WorldEntity's cell-field docs). 0 → helper no-ops.

src/AcDream.Core/Physics/MotionInterpreter.cs

@@ -678,6 +678,14 @@ public sealed class MotionInterpreter : IMotionDoneSink
     /// </summary>
     public Action? RemoveLinkAnimations { get; set; }
 
+    /// <summary>
+    /// #270 diagnostic identity (2026-07-30): the owning entity's server
+    /// guid, stamped by the binding layer so [UM-ACT]/[MT-FAIL] probe lines
+    /// are attributable (probe-identity-attribution lesson). 0 = unset.
+    /// Strip with the #270 probes.
+    /// </summary>
+    public uint DiagnosticGuid { get; set; }
+
     /// <summary>
     /// R3-W4 no-op seam standing in for retail
     /// <c>CPhysicsObj::InitializeMotionTables</c>, called from
@@ -2779,7 +2787,7 @@ public sealed class MotionInterpreter : IMotionDoneSink
                 if (PhysicsDiagnostics.DumpMotionEnabled)
                 {
                     Console.WriteLine(
-                        $"[UM-ACT] cmd=0x{a.Command:X8} stamp={incoming} stored={stored} "
+                        $"[UM-ACT] guid={DiagnosticGuid:X8} cmd=0x{a.Command:X8} stamp={incoming} stored={stored} "
                         + $"newer={newer} auton={a.Autonomous} localSkip={IsLocalPlayer && a.Autonomous}");
                 }
 
@@ -3038,8 +3046,10 @@ public sealed class MotionInterpreter : IMotionDoneSink
             if (!dispatchOk && PhysicsDiagnostics.DumpMotionEnabled)
             {
                 Console.WriteLine(
-                    $"[MT-FAIL] motion=0x{motion:X8} speed={p.Speed:F2} "
-                    + $"style=0x{InterpretedState.CurrentStyle:X8} substate=0x{InterpretedState.ForwardCommand:X8}");
+                    $"[MT-FAIL] guid={DiagnosticGuid:X8} motion=0x{motion:X8} speed={p.Speed:F2} "
+                    + $"style=0x{InterpretedState.CurrentStyle:X8} substate=0x{InterpretedState.ForwardCommand:X8} "
+                    + $"contact={PhysicsObj.TransientState.HasFlag(TransientStateFlags.Contact)} "
+                    + $"walkable={PhysicsObj.TransientState.HasFlag(TransientStateFlags.OnWalkable)}");
             }
 
             if (!dispatchOk)