fix(runtime/core): Slice 5.3 review corrections — retirement/transit close, per-unit pricing, guarded auto-close dispatch

The adversarial review's three blocking findings, each fixed at root:

1. A vendor session now CLOSES when its entity retires (despawn,
   death, ObjectDelete) and at teleport BEGIN
   (HasPendingTeleportStart || IsTeleportActive at the existing
   per-frame seam — both hosts funnel through
   RuntimeWorldTransitState.TryQueueTeleportStart, which flips the
   pending flag strictly before activation). The previous permissive
   early-return stranded the session forever: panel pinned to a stale
   guid, ActiveVendorId swallowing Use for the rest of the session.
2. VendorShopItem carries the desc's stack size, and
   VendorPricing.PerUnitValue ports retail's stack-total division
   (VendorProfile::VendorSellPrice 0x005D1B00: <= 0 guard, integer
   division) — a stack of 50 arrows now prices per arrow, not at 50x.
3. VendorState.Close() guards its observer fanout with the
   dispatcher's catch-and-log semantics — a throwing panel listener
   can no longer propagate into the unprotected per-frame path.

Register honesty rides along: the 0.6 m UseRadius fallback was
acdream's invention (ACE's CheckClose has no fallback; retail passes
the raw authored radius) — removed, the watcher now uses the raw
radius and AP-160's citations are corrected and extended with the
accepted-position-snapshot cadence; AD-72 files VendorPricing's
double-vs-x87-extended narrowing (AD-33's class, bounded by the
±0.1 margin).

Nine tests added. Clean-room complete solution: 11,311 passed /
4 skipped / 0 failed.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

tests/AcDream.Core.Tests/Items/VendorStateTests.cs

@@ -120,6 +120,26 @@ public sealed class VendorStateTests
         Assert.Equal(0u, change.VendorId);
     }
 
+    [Fact]
+    public void Close_ThrowingObserver_DoesNotPropagateAndStillClosesTheSession()
+    {
+        // Slice 5.3 review fix 3: unlike Reset(), Close() must never
+        // rethrow — its production caller (RuntimeVendorRangeQuery.
+        // EnforceRange) runs inside an unprotected per-frame callback.
+        var state = new VendorState();
+        state.Apply(0x40000007u, default, Array.Empty<VendorShopItem>());
+
+        bool secondObserverRan = false;
+        state.Changed += _ => throw new InvalidOperationException("boom");
+        state.Changed += _ => secondObserverRan = true;
+
+        Exception? thrown = Record.Exception(() => { state.Close(); });
+
+        Assert.Null(thrown);
+        Assert.True(secondObserverRan);
+        Assert.Equal(0u, state.VendorId);
+    }
+
     [Fact]
     public void Reset_RetryRepublishesAndOneObserverCannotStarveAnother()
     {