Budget the jump-link layer in pixels of line, nearest the view's centre first

With the drawn set following the view, the layer at 8 pc cost the integrated Radeon 503 ms a frame
at 30 pc from the Sun. Measured, the cost follows the length of line on screen (about 10 ms per
million pixels near the Sun), not the number of links: 100 000 links were 12 ms at the opening
view, 25 000 were 61 ms at 30 pc. So the budget is a length: a million pixels, turned into parsecs
at the depth the view is centred on, spent on the links nearest that centre by their nearer end.
Orbiting with links at 8 pc on the iGPU: 12-18 ms p50 at every pose measured, no long tasks.

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

@@ -7,7 +7,7 @@
  * answers them in place where one does not.
  */
 
-import { jumpLinkSegments, minimumRangeBetween, Route, routeBetween } from './jump-links';
+import { jumpLinkSegments, LinkBudget, minimumRangeBetween, Route, routeBetween } from './jump-links';
 import { StarNeighbourhood } from './star-neighbourhood';
 
 /** The catalogue, sent once: ids, and positions packed three to a star in the same order. */
@@ -19,8 +19,11 @@ export interface RoutingCatalogue {
 
 export type RoutingRequest =
   | { readonly kind: 'route'; readonly requestId: number; readonly fromId: number; readonly toId: number; readonly rangePc: number; readonly ceilingPc: 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 };
+  /**
+   * `drawn` is the stars the map is drawing, as positions in the catalogue that was sent: only they
+   * are linked. `budget`, where given, keeps only the links nearest the view that fit its length.
+   */
+  | { readonly kind: 'links'; readonly requestId: number; readonly rangePc: number; readonly drawn: Uint32Array; readonly budget?: LinkBudget };
 
 export type RoutingResponse =
   | { readonly kind: 'route'; readonly requestId: number; readonly route: Route | null; readonly neededRangePc: number | null }
@@ -42,7 +45,7 @@ export function answerRouting(index: StarNeighbourhood, request: RoutingRequest)
     // 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) };
+    return { kind: 'links', requestId: request.requestId, segments: jumpLinkSegments(drawn, request.rangePc, request.budget) };
   }
   const route = routeBetween(index, request.fromId, request.toId, request.rangePc);
   return {