fix(physics): #307 — PreviousTeleport was always 0 on the live Position path

Shipped defect in route 2 (9966b531), found while reviewing route 4a.

`InboundPhysicsStateController.TryApplyPosition` built its AcceptedPhysicsTimestamps
via `Current(gate, teleportAdvanced: ...)`, omitting `previousTeleport`, which
defaulted to a literal 0. The only site that populated it was the deferred
initial-create path — which is why the continuation executor was correct and
every newer consumer was not.

Consequence in shipped code: route 2 feeds this into
`ValidAcceptedAuthority`, which requires Previous == Accepted for a
ForcePosition. Any local player whose TELEPORT_TS is nonzero — anyone who has
portalled or recalled this session — had the authority rejected and the force
correction SILENTLY DROPPED. The user's @pklite acceptance was genuine but
narrow: that character had not teleported, so the stamp was still 0.

Second latent consequence: with an accepted stamp >= 0x8000, wrap-safe
TeleportRegressed also fires against the 0 and rejects ordinary Apply positions,
not just ForcePosition.

The fix captures `previousTeleport = gate.TeleportTimestamp` BEFORE
`TryAcceptPositionEvent` mutates it, matching the shape the deferred path
already used. Ordering is the whole point: capturing after would make
Previous == Accepted unconditionally, so ValidAcceptedAuthority's check would
pass vacuously — the symptom would disappear while the semantics broke.

Also removes the footgun that allowed it. `Current`'s parameter is now
`ushort? previousTeleport = null` resolving to `gate.TeleportTimestamp`, so the
eleven non-Position channels — none of which can move TELEPORT_TS — get
"previous == current" by omission rather than a literal 0 that is
indistinguishable from a genuine "never teleported".

Consumer audit: only TryApplyPosition was defective. The two route-2 call sites
trace back to it; the RuntimeEntityObjectLifetime sites source from
TryAcceptDeferredPosition and were already correct.

Tests discrimination-verified by reverting the argument to 0: the stamp test
fails Expected 10 / Actual 0, and the classifier test fails Expected
SetPositionSimple / Actual RejectedAuthority — the shipped defect reproduced
exactly.

Gates: complete Release solution 10,935 passed / 4 skipped / 0 failed.

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

src/AcDream.Runtime/Entities/InboundPhysicsStateController.cs

@@ -624,8 +624,16 @@ public sealed class InboundPhysicsStateController
             return false;
         }
 
+        // #307: TryAcceptPositionEvent MUTATES gate.TeleportTimestamp, so the
+        // pre-event value must be captured BEFORE the call - the exact shape
+        // TryAcceptDeferredPosition already used. Reading it afterwards would
+        // yield the accepted value and make Previous == Accepted vacuously
+        // true; omitting it (the original defect) left it 0, which made every
+        // downstream ValidAcceptedAuthority ForcePosition check fail for any
+        // entity whose TELEPORT_TS had ever advanced.
+        ushort previousTeleport = gate.TeleportTimestamp;
         bool advancesTeleport = PhysicsTimestampGate.IsNewer(
-            gate.TeleportTimestamp,
+            previousTeleport,
             update.TeleportSequence);
         disposition = gate.TryAcceptPositionEvent(
             update.InstanceSequence,
@@ -636,7 +644,8 @@ public sealed class InboundPhysicsStateController
         timestamps = Current(
             gate,
             teleportAdvanced: disposition is PositionTimestampDisposition.Apply
-                && advancesTeleport);
+                && advancesTeleport,
+            previousTeleport: previousTeleport);
         accepted = ApplyAcceptedPosition(
             old,
             update,
@@ -1113,17 +1122,28 @@ public sealed class InboundPhysicsStateController
             0,
             spawn.InstanceSequence);
 
+    /// <summary>
+    /// #307: <paramref name="previousTeleport"/> is the TELEPORT_TS value the
+    /// gate held BEFORE the event this call is stamping. Only the two Position
+    /// entry points can move that channel, so they pass their own pre-event
+    /// capture; every other channel leaves it untouched and therefore gets
+    /// "previous == current" by omission. The parameter deliberately has NO
+    /// zero default: a literal 0 is a legal, common TELEPORT_TS, so a silent
+    /// zero is indistinguishable from a genuine "never teleported" and reads
+    /// as a spurious teleport regression to
+    /// <c>RuntimeAuthoritativePositionRouteClassifier</c>.
+    /// </summary>
     private static AcceptedPhysicsTimestamps Current(
         PhysicsTimestampGate gate,
         bool teleportAdvanced = false,
-        ushort previousTeleport = 0) => new(
+        ushort? previousTeleport = null) => new(
         gate.InstanceTimestamp,
         gate.ServerControlledMoveTimestamp,
         gate.TeleportTimestamp,
         gate.ForcePositionTimestamp,
         teleportAdvanced,
         TeleportHookRequired: false,
-        previousTeleport);
+        previousTeleport ?? gate.TeleportTimestamp);
 
     private static WorldSession.EntitySpawn MergeUntimestampedCreate(
         WorldSession.EntitySpawn retained,