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

One-line per-call emission helper for the FindCollisions dispatcher
instrumentation site. Captures path-selection state (collide flag,
insertType, objState) + walk-interp + return state for direct
comparison to retail's BSPTREE::find_collisions breakpoint.
Output uses the [push-back-disp] tag to disambiguate from
[push-back] adjust-sphere events.

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

src/AcDream.Core/Physics/PhysicsDiagnostics.cs

@@ -348,6 +348,44 @@ public static class PhysicsDiagnostics
             dpPos, dpMove, iDist, applied));
     }
 
+    /// <summary>
+    /// A6.P1 emission helper for the <c>FindCollisions</c> dispatcher
+    /// site. One line per call: input sphere center, movement vector,
+    /// path-selection state flags (collide / insertType / objState),
+    /// walk-interp at entry, and the return state. Direct paired
+    /// comparison to retail's cdb breakpoint on
+    /// <c>BSPTREE::find_collisions</c>.
+    ///
+    /// <para>
+    /// Caller MUST guard with <c>if (!ProbePushBackEnabled) return;</c>
+    /// before calling.
+    /// </para>
+    /// </summary>
+    public static void LogPushBackDispatch(
+        Vector3 sphereCenter,
+        Vector3 movement,
+        bool    collide,
+        int     insertType,
+        int     objState,
+        float   walkInterpEntry,
+        int     returnState)
+    {
+        // Output format mirrors LogPushBackAdjust: single string.Format
+        // with CultureInfo.InvariantCulture so the F4 / hex formatting is
+        // locale-independent and the output is greppable.
+        var ci = System.Globalization.CultureInfo.InvariantCulture;
+        Console.WriteLine(string.Format(ci,
+            "[push-back-disp] site=dispatch " +
+            "center=({0:F4},{1:F4},{2:F4}) " +
+            "mvmt=({3:F4},{4:F4},{5:F4}) " +
+            "collide={6} insertType={7} objState=0x{8:X} " +
+            "winterp={9:F4} return={10}",
+            sphereCenter.X, sphereCenter.Y, sphereCenter.Z,
+            movement.X, movement.Y, movement.Z,
+            collide, insertType, objState,
+            walkInterpEntry, returnState));
+    }
+
     public static void LogCpBoolWrite(string field, bool oldValue, bool newValue)
     {
         var caller = GetCpCallerName();