feat(physics): A6.P1 — add LogPushBackCellTransit helper

One-line per-iteration emission helper for the CheckOtherCells
multi-cell BSP loop. Captures primary/other cell ids, BSP result,
and halted flag for direct comparison to retail's
CTransition::check_other_cells loop.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/AcDream.Core/Physics/PhysicsDiagnostics.cs

@@ -386,6 +386,34 @@ public static class PhysicsDiagnostics
             walkInterpEntry, returnState));
     }
 
+    /// <summary>
+    /// A6.P1 emission helper for the <c>CheckOtherCells</c> multi-cell
+    /// BSP iteration site. One line per off-cell hit: from-cell, to-cell,
+    /// BSP result (Ok / Adjusted / Slid / Collided), and the iteration
+    /// outcome. Direct paired comparison to retail's
+    /// <c>CTransition::check_other_cells</c> loop at decomp line
+    /// 272717. Augments the existing A4 multi-cell BSP instrumentation
+    /// with explicit per-iteration outcome telemetry.
+    ///
+    /// <para>
+    /// Caller MUST guard with <c>if (!ProbePushBackEnabled) return;</c>
+    /// before calling.
+    /// </para>
+    /// </summary>
+    public static void LogPushBackCellTransit(
+        uint   primaryCellId,
+        uint   otherCellId,
+        int    bspResult,
+        bool   halted)
+    {
+        var ci = System.Globalization.CultureInfo.InvariantCulture;
+        Console.WriteLine(string.Format(ci,
+            "[push-back-cell] site=other_cell " +
+            "primary=0x{0:X8} other=0x{1:X8} " +
+            "bspResult={2} halted={3}",
+            primaryCellId, otherCellId, bspResult, halted));
+    }
+
     public static void LogCpBoolWrite(string field, bool oldValue, bool newValue)
     {
         var caller = GetCpCallerName();