diff --git a/plugin-designs/doxa-research-map/research-map.vue b/plugin-designs/doxa-research-map/research-map.vue
index 95a107aa1..1532dcac8 100644
--- a/plugin-designs/doxa-research-map/research-map.vue
+++ b/plugin-designs/doxa-research-map/research-map.vue
@@ -1111,6 +1111,26 @@ function _buildFlatLegendMatchExpr(node, legendType) {
 const REGION_IDLE_FILL  = ['case', ['has', 'iso_3166_1_alpha_3'], 0.7, 0.7]
 const REGION_IDLE_COLOR = ['case', ['has', 'iso_3166_1_alpha_3'], 'rgba(60,60,80,0.35)', 'rgba(60,60,80,0.35)']
 const REGION_IDLE_WIDTH = ['case', ['has', 'iso_3166_1_alpha_3'], 0.6, 0.6]
+// Make the region paints data-driven WITHOUT changing what they show: each property is read back and
+// re-written wrapped in a case whose two branches are the value it already had. A property the layer
+// does not define is skipped rather than invented, and one already wrapped is left alone.
+function prewarmRegionPaint(m) {
+  if (!m || !m.getLayer('regions-fill')) return
+  const wrap = (v) => ['case', ['has', 'iso_3166_1_alpha_3'], v, v]
+  const warm = (layer, prop) => {
+    if (!m.getLayer(layer)) return
+    const cur = m.getPaintProperty(layer, prop)
+    if (cur === undefined || cur === null) return
+    if (Array.isArray(cur) && cur[0] === 'case') return
+    m.setPaintProperty(layer, prop, wrap(cur))
+  }
+  try {
+    warm('regions-fill', 'fill-opacity')
+    warm('regions-border', 'line-color')
+    warm('regions-border', 'line-width')
+  } catch (_) { /* style still loading - the first real paint carries it */ }
+}
+
 function paintRegionScope(m, isoCodes) {
   if (!m || !m.getLayer('regions-fill')) return
   // ★ CANONICAL FIRST, OR THE COMPARE BELOW IS A LIE (rega, L43: still 9 writes per click, not 3).
@@ -1618,9 +1638,20 @@ async function ensureRegionsLoaded() {
         // ★ PRE-WARM HERE, which is the only moment that helps. These layers are added on first visit
         // to the Regions tab, and rega measured the first ROW click paying 5.5 s (MapLibre) / 11.1 s
         // (Mapbox) of shader compile because that click was when their paint first became data-driven.
-        // Painting the idle state through paintRegionScope makes it data-driven from the first draw, so
-        // the variant compiles here — where a 6.4 MB GeoJSON is already loading — instead of mid-gesture.
-        paintRegionScope(map.value, [])
+        // Making the paint data-driven at layer-add moves that compile here, where a 6.4 MB GeoJSON is
+        // already loading, instead of into the middle of a gesture.
+        //
+        // WARNING IT WRAPS WHAT THE LAYER ALREADY PAINTS, and does NOT paint the cleared state. The
+        // first version called paintRegionScope(map.value, []) — the CLEARED look, flat grey borders at
+        // width 0.6. addRegionsLayer does not start there: it sets line-color to the region-coloured
+        // match expression and line-width 1 (useMapLayers). So pre-warming with the cleared values
+        // silently repainted every border grey and thinner the moment the layer appeared — a visible
+        // change nobody asked for, and invisible to both things being measured at the time, a timing
+        // check and a write count.
+        // Reading each property back and re-writing it wrapped in an identical-branch case keeps the
+        // appearance exactly as the layer defined it while still making the property data-driven, which
+        // is all the shader variant depends on.
+        prewarmRegionPaint(map.value)
         // Hide regions on non-Doxa-Regions tabs so they don't show through.
         if (map.value.getLayer('regions-fill') && activeTab.value?.id !== 'doxa-regions') {
           map.value.setLayoutProperty('regions-fill',   'visibility', 'none')