--- a/sway/desktop/layer_shell.c
+++ b/sway/desktop/layer_shell.c
@@ -1,3 +1,6 @@
+#include <stdio.h>
+#include <time.h>
+#include "sway/tree/root.h"
 #include <scenefx/types/wlr_scene.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -340,7 +343,26 @@
 
 	struct wlr_layer_surface_v1 *layer_surface = surface->layer_surface;
 
-	// Rerender the optimized blur on change
+	/* WHY: verify actual source ownership before interpreting cache invalidation.
+     * CONTRACT: passive private trace; reads borrowed scene/surface pointers.
+     * INVARIANT: no extra dirty call or change to commit/arrangement order. */
+    if (getenv("OPT_TRACE")) {
+        struct timespec t; clock_gettime(CLOCK_MONOTONIC, &t);
+        struct wlr_surface *s = layer_surface->surface;
+        int x = 0, y = 0; bool valid = wlr_scene_node_coords(&surface->scene->tree->node, &x, &y);
+        fprintf(stderr, "OPT_BACKGROUND_COMMIT ns=%lld output=%s surface=%p resource=%u buffer=%p seq=%u layer=%u mapped=%d coords=%d,%d valid=%d tree=%p parent=%p layer_parent=%p background=%p background_parent=%p global_background=%p bottom=%p blur_tree=%p opt_node=%p opt_parent=%p damage=%d,%d,%d,%d namespace=%s\n",
+            (long long)t.tv_sec * 1000000000LL + t.tv_nsec, surface->output ? surface->output->wlr_output->name : "none",
+            (void *)s, wl_resource_get_id(s->resource), (void *)s->buffer, s->current.seq, layer_surface->current.layer, s->mapped, x, y, valid,
+            (void *)surface->scene->tree, (void *)surface->scene->tree->node.parent, (void *)surface->tree->node.parent,
+            surface->output ? (void *)surface->output->layers.shell_background : NULL,
+            surface->output ? (void *)surface->output->layers.shell_background->node.parent : NULL, (void *)root->layers.shell_background,
+            surface->output ? (void *)surface->output->layers.shell_bottom : NULL,
+            (void *)root->layers.blur_tree, surface->output ? (void *)surface->output->layers.blur_layer : NULL,
+            surface->output ? (void *)surface->output->layers.blur_layer->node.parent : NULL,
+            s->buffer_damage.extents.x1, s->buffer_damage.extents.y1, s->buffer_damage.extents.x2, s->buffer_damage.extents.y2,
+            layer_surface->namespace);
+    }
+    // Rerender the optimized blur on change
 	if (layer_surface->current.layer ==
 			ZWLR_LAYER_SHELL_V1_LAYER_BACKGROUND ||
 		layer_surface->current.layer == ZWLR_LAYER_SHELL_V1_LAYER_BOTTOM) {