Add 6-char subsquare grid overlay and fix map edge rendering

- Show subsquares (5' x 2.5') at zoom >= 11 with lighter styling
- Pad map bounds by 10% so edge tiles always have score data
- Re-send bounds after 500ms to catch late container layout changes

assets/js/maidenhead_grid.ts

@@ -73,25 +73,29 @@ function drawGridSquare(
       c.south > bounds.getNorth() || c.north < bounds.getSouth()) return
 
   const field = precision <= 2
+  const sub = precision >= 6
+  const weight = field ? 2.5 : sub ? 1 : 2
+  const opacity = sub ? 0.5 : 0.8
 
   layerGroup.addLayer(L.rectangle(
     [[c.south, c.west], [c.north, c.east]],
-    { color: "#E63946", weight: field ? 2.5 : 2, opacity: 0.8, fillOpacity: 0, interactive: false }
+    { color: "#E63946", weight, opacity, fillOpacity: 0, interactive: false }
   ))
 
   const sw = map.latLngToContainerPoint([c.south, c.west])
   const ne = map.latLngToContainerPoint([c.north, c.east])
   const px = Math.abs(ne.x - sw.x)
-  const minW = field ? 30 : 40
+  const minW = sub ? 25 : field ? 30 : 40
   if (px > minW) {
-    const len = field ? 2 : 4
-    const text = grid.substring(0, len)
-    const fs = Math.max(10, Math.min(14, Math.round(px / (len * 1.2))))
+    // Subsquares show just the last 2 chars (e.g. "kp"), others show full label
+    const text = sub ? grid.substring(4, 6) : grid.substring(0, field ? 2 : 4)
+    const len = text.length
+    const fs = Math.max(9, Math.min(sub ? 12 : 14, Math.round(px / (len * 1.2))))
     layerGroup.addLayer(L.marker([c.center.lat, c.center.lon], {
       interactive: false,
       icon: L.divIcon({
         className: "grid-label",
-        html: `<div style="font-size:${fs}px;font-weight:bold;color:#fff;background:rgba(0,0,0,0.5);padding:1px 4px;border-radius:3px;white-space:nowrap;width:fit-content;">${text}</div>`,
+        html: `<div style="font-size:${fs}px;font-weight:${sub ? "normal" : "bold"};color:#fff;background:rgba(0,0,0,${sub ? "0.35" : "0.5"});padding:1px 4px;border-radius:3px;white-space:nowrap;width:fit-content;">${text}</div>`,
         iconSize: [Math.round(len * fs * 0.8), Math.round(fs * 1.5)],
         iconAnchor: [Math.round(len * fs * 0.4), Math.round(fs * 0.75)]
       })
@@ -105,6 +109,7 @@ export function updateGridOverlay(map: L.Map, gridLayer: L.LayerGroup): void {
   const bounds = map.getBounds()
   const zoom = map.getZoom()
   const showSquares = zoom >= 7
+  const showSubsquares = zoom >= 11
 
   const south = Math.max(bounds.getSouth(), -90)
   const north = Math.min(bounds.getNorth(), 90)
@@ -133,8 +138,32 @@ export function updateGridOverlay(map: L.Map, gridLayer: L.LayerGroup): void {
   for (let lon = wE; lon < eE; lon += 2) {
     for (let lat = sE; lat < nE; lat += 1) {
       const nLon = ((lon % 360) + 540) % 360 - 180
-      const g = new GridSquare(lat + 0.5, nLon + 1).encode(4)
-      drawGridSquare(g.substring(0, 4), 4, bounds, gridLayer, drawn, map)
+
+      if (showSubsquares) {
+        // Draw the 4-char square boundary first
+        const sq = new GridSquare(lat + 0.5, nLon + 1).encode(4)
+        drawGridSquare(sq.substring(0, 4), 4, bounds, gridLayer, drawn, map)
+
+        // Then draw 6-char subsquares (24 x 24 = 576 per square, 5' x 2.5')
+        const subW = 5 / 60
+        const subH = 2.5 / 60
+        const startI = Math.max(0, Math.floor((bounds.getWest() - lon) / subW))
+        const endI = Math.min(24, Math.ceil((bounds.getEast() - lon) / subW))
+        const startJ = Math.max(0, Math.floor((bounds.getSouth() - lat) / subH))
+        const endJ = Math.min(24, Math.ceil((bounds.getNorth() - lat) / subH))
+
+        for (let i = startI; i < endI; i++) {
+          for (let j = startJ; j < endJ; j++) {
+            const cLon = nLon + i * subW + subW / 2
+            const cLat = lat + j * subH + subH / 2
+            const sub = new GridSquare(cLat, cLon).encode(6)
+            drawGridSquare(sub, 6, bounds, gridLayer, drawn, map)
+          }
+        }
+      } else {
+        const g = new GridSquare(lat + 0.5, nLon + 1).encode(4)
+        drawGridSquare(g.substring(0, 4), 4, bounds, gridLayer, drawn, map)
+      }
     }
   }
 }

assets/js/propagation_map_hook.ts

@@ -852,6 +852,8 @@ export const PropagationMap: Record<string, unknown> & {
     this.el.addEventListener("show-loading", () => topbar.show(300))
 
     requestAnimationFrame(() => this.sendBounds())
+    // Re-check bounds after layout settles (sidebar, fonts, etc.)
+    setTimeout(() => { this.map.invalidateSize(); this.sendBounds() }, 500)
     this.map.on("moveend", () => {
       this.sendBounds()
       if (this.gridVisible) {
@@ -1124,7 +1126,8 @@ export const PropagationMap: Record<string, unknown> & {
 
   sendBounds(this: PropagationMapHook) {
     topbar.show()
-    const b = this.map.getBounds()
+    // Pad bounds by ~0.5° so Leaflet edge tiles always have data to render
+    const b = this.map.getBounds().pad(0.1)
     this.pushEvent("map_bounds", {
       south: b.getSouth(),
       north: b.getNorth(),