--- a/src/sliding_fb.rs	Wed Jul 22 16:48:22 2026 -0500
+++ b/src/sliding_fb.rs	Sun Jul 26 17:30:51 2026 -0500
@@ -1092,14 +1092,14 @@
         // Merge spikes.
         // This crucially expects the merge routine to be stable with respect to spike locations,
         // and not to performing any pruning. That is be to done below simultaneously for γ.
-        if config.insertion.merge_now(&state) {
+        config.insertion.if_merge_now(&state, |ins| {
             let m = prox_penalty.merge_spikes(
                 &mut μ,
                 &mut τv̆,
                 &μ̆,
                 τ,
                 ε,
-                &config.insertion,
+                ins,
                 &reg,
                 Some(|μ̃: &RNDM<N, F>| f.apply(μ̃)),
             );
@@ -1107,7 +1107,7 @@
             stats.merged += m;
             //v = f.differential(&μ);
             //}
-        }
+        });
 
         γ.prune_compat(&mut μ, &mut stats);