Route with A* over numeric cell keys, so a route can reach past the Sun's crowd

The route search widened evenly from the departure, Dijkstra-style, with a
budget of 20 000 stars. On the Gaia catalogue those are all within about
40 pc of the Sun, so it found no route to anything farther at any range:
Sol to Mirfak (155 pc) failed at 3, 8, 15 and 30 pc alike. Every failure
then asked minimumRangeBetween what range would work. That search widened
the same way with a 30 pc ceiling, and it ran for up to a minute on the
main thread before giving up with nothing.

routeBetween is now an A* search. Each star is queued by the distance
travelled to it plus the straight line on to the destination, on a binary
heap rather than a linear scan of the frontier. It heads for the
destination instead of flooding the core around the departure.

minimumRangeBetween bisects the range, one routeBetween per step, because
whether a chain exists can only become truer as the range grows. Its
answer is always the longest hop of a route actually found, so a range it
names always opens one. Its ceiling is now the Routes panel's own
maximum, MAX_JUMP_RANGE_PC: a range the control cannot be set to is no
answer, and raiseTo already clamped any figure above it.

The spatial index keys its cells by one number packed from their three
indices instead of an "ix,iy,iz" string. A search visits up to 125 cells
for every star it expands, and building those strings was half of what a
route cost. forEachWithin hands neighbours over unsorted and uncollected,
which was most of the other half; within is now that, gathered and sorted.

The no-route line said nothing in the catalogue bridged the gap; it now
says no chain of jumps up to the panel's maximum reaches the star, which
is what was searched.

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

src/app/features/galaxy-system/galaxy-system-scene.component.ts

@@ -39,6 +39,7 @@ import { SystemObjectCardComponent } from './system-object-card.component';
 import { colorIndexToRgb, StarFieldRenderer, starRenderBudgetFromUrl } from './star-field-renderer';
 import { collectJumpLinks, minimumRangeBetween, routeBetween } from '../../shared/astro/jump-links';
 import { StarNeighbourhood } from '../../shared/astro/star-neighbourhood';
+import { MAX_JUMP_RANGE_PC } from '../hud/routes-panel.component';
 import { HostStarRings } from './host-star-rings';
 import { JumpLinkRenderer } from './jump-link-renderer';
 import { ReservedBox, ringPlacement } from './label-ring';
@@ -83,10 +84,11 @@ const PLAN_ZOOM_SPAN = 64;
 const ROUTE_OPTION_COUNT = 6;
 const MIN_ROUTE_QUERY_LENGTH = 2;
 /**
- * The widest crossing `minimumRangeBetween` will consider when saying what a route would need.
- * Beyond this the catalogue is one component and the answer stops being informative.
+ * The widest crossing `minimumRangeBetween` will consider when saying what a route would need:
+ * the Routes panel's own maximum, since a range the control cannot be set to is no answer. At
+ * 30 pc, as it was, the search could run for a minute through the dense core before answering.
  */
-const ROUTE_RANGE_CEILING_PC = 30;
+const ROUTE_RANGE_CEILING_PC = MAX_JUMP_RANGE_PC;
 
 /** How many neighbouring stars are named from inside a system. */
 const NEIGHBOUR_COUNT = 4;

src/app/features/hud/routes-panel.component.ts

@@ -2,6 +2,12 @@ import { ChangeDetectionStrategy, Component, computed, input, output, signal } f
 
 import { formatParsecs } from '../../shared/format/quantity';
 
+/**
+ * The widest jump the Routes panel offers. Past it the drawn graph is a solid sheet of lines, and
+ * a route search through the dense core around the Sun walks thousands of stars at every step.
+ */
+export const MAX_JUMP_RANGE_PC = 8;
+
 /** A star offered for one of the two fields, as the panel needs to show it. */
 export interface RouteStarOption {
   readonly id: number;
@@ -117,7 +123,7 @@ type Field = 'from' | 'to';
                   {{ format(plotted.neededRangePc) }} would reach.
                 </button>
               } @else {
-                Nothing in the catalogue bridges the gap.
+                No chain of jumps up to {{ format(maxRangePc) }} reaches it.
               }
             </p>
           }
@@ -160,8 +166,7 @@ export class RoutesPanelComponent {
   readonly fields: readonly Field[] = ['from', 'to'];
   /** A tenth of a parsec is finer than the catalogue's own distances are known to. */
   readonly minRangePc = 0.5;
-  /** Beyond this the graph is a solid sheet of lines and every pair of stars is connected. */
-  readonly maxRangePc = 8;
+  readonly maxRangePc = MAX_JUMP_RANGE_PC;
 
   readonly rangePc = signal(3);
   readonly open = signal<Field | null>(null);