From bbeb0b95a7eea722dbc5273750f0a84b1460becc Mon Sep 17 00:00:00 2001
From: Yuval Tassa <tassa@google.com>
Date: Mon, 13 Oct 2025 06:17:41 -0700
Subject: [PATCH] Reset contact `efc_address` in `mj_clearEfc`, fixes #2869

The truth is that all these solver-related values should be moved out of `mjContact` altogether, but that can be done in a future followup.

PiperOrigin-RevId: 818624976
Change-Id: I5b9e63927098cdf26b9f8acfdd9d86e75d6ce331
---
 src/engine/engine_memory.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/engine/engine_memory.h b/src/engine/engine_memory.h
index c232b20f..3202353d 100644
--- a/src/engine/engine_memory.h
+++ b/src/engine/engine_memory.h
@@ -75,6 +75,11 @@ static inline void mj_clearEfc(mjData* d) {
   d->nefc = 0;
   d->nisland = 0;
   d->contact = (mjContact*) d->arena;
+
+  // if any contacts are allocated, clear their efc_address
+  for (int i=0; i < d->ncon; i++) {
+    d->contact[i].efc_address = -1;
+  }
 }
 
 #ifdef __cplusplus