feat(scamin): honor SCAMIN exactly for light sectors

The LIGHTS06 sector figure (arcs/legs) was the one discrete light mark
not getting exact SCAMIN: its flare (point_symbols) and characteristic
text already bucket, but the baker dumped the sector geometry into the
shared `lines` source-layer with NO scamin tag, gated only to integer
floor(z*) by tile content — so sectors popped in up to ~1 zoom too
early when zooming out.

Baker: tag each sector with its parent LIGHTS' SCAMIN and emit it into
its OWN `sector_lines` source-layer (not the shared `lines`), so it can
be bucketed without fanning every coastline/contour into per-SCAMIN
variants. Also stop clamping a sector's tile-availability floor to
bandMin, matching the flare prim, so a SCAMIN-below-band sector stays
available down to its SCAMIN scale.

Client: add `sector_lines` to SCAMIN_BUCKET_LAYERS and two thin style
layers (solid/dashed) mirroring lines-solid/lines-dashed. Sectors now
cut at the exact fractional scale, both directions, like the flare/text.

General `lines`/`areas` deliberately left unbucketed: they're
continuous / best-available gap-fill, where SCAMIN-removal is a
separate (hole-punching) concern.

Requires a re-bake (the `scamin` tag + `sector_lines` layer are new
baked data).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: beetlebugorg

internal/engine/bake/bake.go

@@ -262,6 +262,7 @@ type sectorPrim struct {
 	cat      int
 	zMin     uint32
 	natMax   uint32
+	scamin   uint32 // SCAMIN denominator of the parent LIGHTS (0 = none); emitted as `scamin` so the client's per-SCAMIN bucket layer gates the exact display cutoff, same as point symbols/text
 	// legNorm is the full-length leg reach (VALNMR nominal range) as a fraction
 	// of the normalized world — a fixed GROUND distance, so zoom-independent
 	// (unlike the 25 mm short legs / ring, which are screen-px). Drives the tile
@@ -878,6 +879,7 @@ func (b *Baker) route(p portrayal.Primitive, class string, drawPrio, cat int, zr
 		b.sectors = append(b.sectors, sectorPrim{
 			anchor: v.Anchor, params: v.Sector, class: class, cell: b.curCell,
 			drawPrio: drawPrio, cat: cat, zMin: zMin, natMax: zr.Max,
+			scamin:  b.curScamin,
 			legNorm: sectorLegFullNorm(v.Anchor.Lat, v.Sector.RadiusNM),
 		})
 	}
@@ -1098,10 +1100,11 @@ func (b *Baker) TileCoordsBand(extent, bandMin, bandMax uint32) []tile.TileCoord
 			continue
 		}
 		ax, ay := normX(sp.anchor.Lon), normY(sp.anchor.Lat)
+		// Like the flare prim (see lo := r.zMin above), a SCAMIN-bearing sector may
+		// sit BELOW bandMin — keep it AVAILABLE down to its SCAMIN scale so the
+		// client's per-SCAMIN bucket gates the exact cutoff. Non-SCAMIN sectors have
+		// zMin == bandMin (bandZMin floors them), so this is a no-op for them.
 		lo := sp.zMin
-		if lo < bandMin {
-			lo = bandMin
-		}
 		for z := lo; z <= b.clampZMax(sp.natMax); z++ {
 			r := math.Max(sectorRadiusNorm(z), sp.legNorm)
 			bb := geo.BoundingBox{
@@ -1490,7 +1493,14 @@ func (b *Baker) emitTileInto(coord tile.TileCoord, extent uint32, buffer float64
 			if st.sleg >= 0 {
 				attrs = append(attrs, mvt.KeyValue{Key: "sleg", Value: mvt.IntVal(int64(st.sleg))})
 			}
-			tb.Layer("lines").AddLines(paths, attrs)
+			// SCAMIN of the parent LIGHTS — so the client's per-SCAMIN bucket layer
+			// gates the sector figure at the EXACT display scale, in both directions,
+			// matching the light's flare (point_symbols) and characteristic text. Its
+			// own `sector_lines` layer keeps the bucket fan-out off the shared `lines`.
+			if sp.scamin != 0 {
+				attrs = append(attrs, mvt.KeyValue{Key: "scamin", Value: mvt.IntVal(int64(sp.scamin))})
+			}
+			tb.Layer("sector_lines").AddLines(paths, attrs)
 		}
 	}
 

web/chartplotter.mjs

@@ -117,7 +117,11 @@ const BAND_DISPLAY_MIN = { overview: 0, general: 0, coastal: 10, approach: 12, h
 // track the display scale of the object it annotates — keyed on the SOURCE-LAYER,
 // not the style-layer id, because the text labels fan out into many style layers
 // (text-<halign>-<valign>, light-text) that all read the one `text` source-layer.
-const SCAMIN_BUCKET_LAYERS = new Set(["point_symbols", "soundings", "text"]);
+// `sector_lines` is the LIGHTS06 sector figure (arcs/legs), baked into its own
+// source-layer (not the shared `lines`) precisely so it can be bucketed here
+// without fanning every coastline/contour into per-SCAMIN variants — the sector
+// then cuts at the same exact scale as its light's flare + characteristic text.
+const SCAMIN_BUCKET_LAYERS = new Set(["point_symbols", "soundings", "text", "sector_lines"]);
 
 // The display zoom at which a 1:N (scamin) feature first becomes visible at the
 // given latitude: the zoom whose display-scale denominator equals scamin. FRACTIONAL
@@ -1403,6 +1407,13 @@ export class ChartPlotter extends HTMLElement {
       { id: "lines-solid", type: "line", source: "chart", "source-layer": "lines", filter: ["==", ["coalesce", ["get", "dash"], "solid"], "solid"], paint: { "line-color": this.colorExpr("color_token"), "line-width": ["coalesce", ["get", "width_px"], 1] } },
       { id: "lines-dashed", type: "line", source: "chart", "source-layer": "lines", filter: ["==", ["get", "dash"], "dashed"], paint: { "line-color": this.colorExpr("color_token"), "line-width": ["coalesce", ["get", "width_px"], 1], "line-dasharray": [4, 3] } },
       { id: "lines-dotted", type: "line", source: "chart", "source-layer": "lines", filter: ["all", ["==", ["get", "dash"], "dotted"], ["!", ["has", "danger_depth"]]], paint: { "line-color": this.colorExpr("color_token"), "line-width": ["coalesce", ["get", "width_px"], 1], "line-dasharray": [1, 2] } },
+      // LIGHTS06 sector figure (coloured arcs / OUTLW backing / dashed legs) — its
+      // OWN source-layer so it can be SCAMIN-bucketed (see SCAMIN_BUCKET_LAYERS)
+      // without dragging every coastline/contour into per-SCAMIN variants. Styling
+      // mirrors lines-solid/lines-dashed (the sector tessellation emits only solid
+      // and dashed runs); sleg/category/boundary gating rides combineFilters as before.
+      { id: "sector-lines-solid", type: "line", source: "chart", "source-layer": "sector_lines", filter: ["==", ["coalesce", ["get", "dash"], "solid"], "solid"], paint: { "line-color": this.colorExpr("color_token"), "line-width": ["coalesce", ["get", "width_px"], 1] } },
+      { id: "sector-lines-dashed", type: "line", source: "chart", "source-layer": "sector_lines", filter: ["==", ["get", "dash"], "dashed"], paint: { "line-color": this.colorExpr("color_token"), "line-width": ["coalesce", ["get", "width_px"], 1], "line-dasharray": [4, 3] } },
       // OBSTRN/WRECKS dotted foul boundary (client-side): shown only when the
       // feature's VALSOU is ≤ the live safety contour. Filter updates on
       // safetyContour — no re-bake. Excluded from lines-dotted above.