In kick1 after all is done, update the part's acceleration to include the...

In kick1 after all is done, update the part's acceleration to include the gpart acceleration. This allows the hydro drift to use the correct accelerations for hydro predictions.

src/runner.c

@@ -1001,6 +1001,21 @@ void runner_do_kick1(struct runner *r, struct cell *c, int timer) {
 
         /* do the kick */
         kick_part(p, xp, ti_begin, ti_begin + ti_step / 2, timeBase);
+
+        /* Update the accelerations to be used in the drift for hydro */
+        if (p->gpart != NULL) {
+
+          const float a_tot[3] = {p->a_hydro[0] + p->gpart->a_grav[0],
+                                  p->a_hydro[1] + p->gpart->a_grav[1],
+                                  p->a_hydro[2] + p->gpart->a_grav[2]};
+
+          p->a_hydro[0] = a_tot[0];
+          p->a_hydro[1] = a_tot[1];
+          p->a_hydro[2] = a_tot[2];
+          p->gpart->a_grav[0] = a_tot[0];
+          p->gpart->a_grav[1] = a_tot[1];
+          p->gpart->a_grav[2] = a_tot[2];
+        }
       }
     }