Avoid RSwM3 reject_step! temporaries on the in-place path

src/noise_interfaces/noise_process_interface.jl

@@ -466,7 +466,11 @@ must throw an informative error instead of silently reusing an invalid increment
                 # slot L₂ was popped from.
                 cutLength = L₁ - dtM
                 if cutLength > W.rswm.discard_length
-                    if W.Z == nothing
+                    if isinplace(W)
+                        @.. L₂ -= W.dWtilde
+                        W.Z !== nothing && @.. L₃ -= W.dZtilde
+                        ResettableStacks.copyat_or_push!(W.S₁, (cutLength, L₂, L₃))
+                    elseif W.Z == nothing
                         ResettableStacks.copyat_or_push!(
                             W.S₁, (cutLength, L₂ - W.dWtilde, nothing)
                         )

test/RSwM_correctness_test.jl

@@ -173,4 +173,27 @@
             end
         end
     end
+
+    @testset "RSwM3 in-place S₂ bridge reject_step! does not allocate" begin
+        W = WienerProcess!(
+            0.0, zeros(4), zeros(4);
+            rswm = RSWM(adaptivealg = :RSwM3), rng = Xoshiro(7)
+        )
+        calculate_step!(W, 0.2, nothing, nothing)
+        for _ in 1:50
+            reject_step!(W, 0.5 * W.dt, nothing, nothing)
+            accept_step!(W, 0.2, nothing, nothing)
+        end
+        # Measure through a local function so @allocated sees a compiled call site.
+        # A bare `@allocated reject_step!(...)` after `using` inside `@testset` /
+        # `@safetestset` leaves a 32 B/call world-age artifact on Julia 1.10.
+        measure_reject(W) = @allocated reject_step!(W, 0.5 * W.dt, nothing, nothing)
+        total = 0
+        for _ in 1:100
+            @test !isempty(W.S₂)
+            total += measure_reject(W)
+            accept_step!(W, 0.2, nothing, nothing)
+        end
+        @test total == 0
+    end
 end