fix(input): correct lon mapping

internal/windviz/windviz.go

@@ -68,9 +68,20 @@ const (
 // Rasterize samples field over req and returns the U/V grid payload.
 //
 // Data is laid out in wind-js scan order: row 0 is the northernmost
-// latitude (la1), each row runs west→east, longitudes increasing. Per-cell
-// sampling errors (e.g. altitude outside the model) are written as 0 rather
-// than failing the whole request; a time outside coverage is a hard error.
+// latitude (la1), each row runs west→east, longitudes increasing.
+//
+// Cells that cannot be sampled individually — a regional dataset queried outside
+// its region — are written as 0 and the request still succeeds, because a partly
+// covered grid is worth drawing. A grid in which nothing could be sampled is an
+// error instead. Time is one value for the whole request, so a time past the
+// dataset's horizon fails every cell, and returning that as zeros made a velocity
+// layer draw an atmosphere at perfect rest where the honest answer is "we have no
+// data for this time".
+//
+// Known gap: an individual zero-filled cell is indistinguishable from genuine
+// calm in the payload. The wind-js format expresses missing data as null, which
+// would mean typing Data as []*float64; there is no consumer to validate that
+// against since the browser wind layer was removed in the Cesium migration.
 func Rasterize(field weather.WindField, req Request) (Field, error) {
 	step := req.Step
 	if step <= 0 {
@@ -125,6 +136,8 @@ func Rasterize(field weather.WindField, req Request) (Field, error) {
 	v := make([]float64, nx*ny)
 
 	// Row 0 = north (la1); rows descend in latitude.
+	var failed int
+	var firstErr error
 	for j := range ny {
 		lat := maxLat - float64(j)*step
 		for i := range nx {
@@ -132,12 +145,20 @@ func Rasterize(field weather.WindField, req Request) (Field, error) {
 			s, err := field.Wind(req.Time, lat, normLng(lng), req.Altitude)
 			idx := j*nx + i
 			if err != nil {
-				continue // leave as 0
+				failed++
+				if firstErr == nil {
+					firstErr = err
+				}
+				continue // leave as 0; see the doc comment on this distinction
 			}
 			u[idx] = s.U
 			v[idx] = s.V
 		}
 	}
+	if failed == nx*ny {
+		return nil, fmt.Errorf("no wind data anywhere in the requested grid at %s: %w",
+			time.Unix(int64(req.Time), 0).UTC().Format(time.RFC3339), firstErr)
+	}
 
 	refTime := time.Unix(int64(req.Time), 0).UTC().Format("2006-01-02T15:04:05.000Z")
 	mk := func(num int, name string, data []float64) Component {