Link only the stars that are drawn

The jump-link graph linked the whole catalogue: 3.7 million links at 8 pc, 7.4-7.8 s in the
worker and a 443-515 ms frame on the main thread when they landed, and most of them between stars
that were neither drawn nor clickable. A graph request now carries the star field's drawn stars,
and the worker links only those, over an index of its own with cells as wide as the range. The
scene asks again once a new drawn set has held still for 250 ms.

The renderer is handed the graph's bounding sphere instead of computing it: three.js walked every
vertex on the main thread in the first frame that drew a new graph, 48-55 ms at 8 pc.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016jxMkwA2rbicdGxHosecYi

src/app/shared/astro/routing.ts

@@ -19,7 +19,8 @@ export interface RoutingCatalogue {
 
 export type RoutingRequest =
   | { readonly kind: 'route'; readonly requestId: number; readonly fromId: number; readonly toId: number; readonly rangePc: number; readonly ceilingPc: number }
-  | { readonly kind: 'links'; readonly requestId: number; readonly rangePc: number };
+  /** `drawn` is the stars the map is drawing, as positions in the catalogue that was sent: only they are linked. */
+  | { readonly kind: 'links'; readonly requestId: number; readonly rangePc: number; readonly drawn: Uint32Array };
 
 export type RoutingResponse =
   | { readonly kind: 'route'; readonly requestId: number; readonly route: Route | null; readonly neededRangePc: number | null }
@@ -38,7 +39,10 @@ export function indexCatalogue({ ids, positions }: RoutingCatalogue): StarNeighb
  */
 export function answerRouting(index: StarNeighbourhood, request: RoutingRequest): RoutingResponse {
   if (request.kind === 'links') {
-    return { kind: 'links', requestId: request.requestId, segments: jumpLinkSegments(index, request.rangePc) };
+    // An index of its own over the drawn stars, in cells as wide as the range, so each cell is
+    // paired with its immediate neighbours only: 14 cells a cell at 8 pc rather than 63.
+    const drawn = new StarNeighbourhood(Array.from(request.drawn, (at) => index.pointAt(at)), request.rangePc);
+    return { kind: 'links', requestId: request.requestId, segments: jumpLinkSegments(drawn, request.rangePc) };
   }
   const route = routeBetween(index, request.fromId, request.toId, request.rangePc);
   return {