Add Lambert solver, transfer matrix, Dijkstra routing, and route planner UI

- Lambert's problem solver using universal variable method with bisection
  (handles elliptic, parabolic, hyperbolic transfers + anti-podal cases)
- Transfer matrix: precompute pairwise station transfers over time window
  using Lambert solver with configurable launch velocity
- Dijkstra routing on time-expanded graph (station × week nodes, transfer
  + wait edges) to find minimum-time routes
- Route Planner UI: from/to station dropdowns, search window selector
  (1-10 years), "Find Optimal Route" button with results card
- Route visualization: orange dashed trajectory lines with arrow heads
  and leg numbers on the 2D canvas
- Tested: Mercury L1 → Jupiter L1 computes 6-month direct transfer at
  30 km/s — physically reasonable

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/lib/render/canvas2d/SolarSystem2D.ts

@@ -20,6 +20,7 @@ export class SolarSystem2DRenderer {
 	private stationPositions: Float64Array = new Float64Array(0);
 	private stationNames: string[] = [];
 	private showStations: boolean = true;
+	private routeLegs: { from: number; to: number }[] = [];
 	private isDragging = false;
 	private lastMouse = { x: 0, y: 0 };
 	private animFrameId: number = 0;
@@ -86,6 +87,10 @@ export class SolarSystem2DRenderer {
 		this.showStations = visible;
 	}
 
+	updateRoute(legs: { from: number; to: number }[]) {
+		this.routeLegs = legs;
+	}
+
 	render() {
 		const { canvas, ctx } = this;
 		const dpr = window.devicePixelRatio || 1;
@@ -133,6 +138,11 @@ export class SolarSystem2DRenderer {
 			}
 		}
 
+		// Draw route legs
+		if (this.routeLegs.length > 0 && this.stationPositions.length > 0) {
+			this.drawRoute();
+		}
+
 		// Scale indicator
 		this.drawScaleBar(rect.width, rect.height);
 	}
@@ -287,6 +297,58 @@ export class SolarSystem2DRenderer {
 		ctx.fillText(info.name, sx + size + 4, sy + 3);
 	}
 
+	private drawRoute() {
+		const ctx = this.ctx;
+		const colors = ['#ff6a33', '#33ff88', '#ff33aa', '#33aaff', '#ffaa33'];
+
+		for (let i = 0; i < this.routeLegs.length; i++) {
+			const leg = this.routeLegs[i];
+			const fromX = this.stationPositions[leg.from * 3];
+			const fromY = this.stationPositions[leg.from * 3 + 1];
+			const toX = this.stationPositions[leg.to * 3];
+			const toY = this.stationPositions[leg.to * 3 + 1];
+
+			const [sx1, sy1] = this.auToScreen(fromX, fromY);
+			const [sx2, sy2] = this.auToScreen(toX, toY);
+
+			const color = colors[i % colors.length];
+
+			// Draw line
+			ctx.strokeStyle = color;
+			ctx.lineWidth = 2;
+			ctx.setLineDash([6, 4]);
+			ctx.beginPath();
+			ctx.moveTo(sx1, sy1);
+			ctx.lineTo(sx2, sy2);
+			ctx.stroke();
+			ctx.setLineDash([]);
+
+			// Arrow head
+			const angle = Math.atan2(sy2 - sy1, sx2 - sx1);
+			const arrowLen = 8;
+			ctx.fillStyle = color;
+			ctx.beginPath();
+			ctx.moveTo(sx2, sy2);
+			ctx.lineTo(
+				sx2 - arrowLen * Math.cos(angle - 0.3),
+				sy2 - arrowLen * Math.sin(angle - 0.3),
+			);
+			ctx.lineTo(
+				sx2 - arrowLen * Math.cos(angle + 0.3),
+				sy2 - arrowLen * Math.sin(angle + 0.3),
+			);
+			ctx.closePath();
+			ctx.fill();
+
+			// Leg number
+			const mx = (sx1 + sx2) / 2;
+			const my = (sy1 + sy2) / 2;
+			ctx.fillStyle = color;
+			ctx.font = 'bold 10px monospace';
+			ctx.fillText(`${i + 1}`, mx + 5, my - 5);
+		}
+	}
+
 	private drawStation(xAU: number, yAU: number, name: string) {
 		const ctx = this.ctx;
 		const [sx, sy] = this.auToScreen(xAU, yAU);

frontend/src/lib/stores/routing.svelte.ts

@@ -0,0 +1,12 @@
+import type { RouteResult } from '$lib/wasm/bridge';
+
+class RoutingState {
+	fromStation = $state<number | null>(null);
+	toStation = $state<number | null>(null);
+	route = $state<RouteResult | null>(null);
+	isComputing = $state(false);
+	error = $state('');
+	weekWindow = $state(260); // ~5 years search window
+}
+
+export const routing = new RoutingState();

frontend/src/lib/wasm/bridge.ts

@@ -57,3 +57,34 @@ export function getStationNames(stationsJson: string): string[] {
 	if (!wasm) return [];
 	return JSON.parse(wasm.get_station_names(stationsJson));
 }
+
+export interface RouteResult {
+	legs: {
+		from_station: number;
+		to_station: number;
+		departure_week: number;
+		arrival_week: number;
+		wait_weeks: number;
+	}[];
+	total_time_weeks: number;
+	departure_week: number;
+}
+
+export function computeRoute(
+	stationsJson: string,
+	fromStation: number,
+	toStation: number,
+	launchVelocityKms: number,
+	startJd: number,
+	weekWindow: number,
+): RouteResult | null {
+	const wasm = getWasm();
+	if (!wasm) return null;
+	const json = wasm.compute_route(stationsJson, fromStation, toStation, launchVelocityKms, startJd, weekWindow);
+	if (!json) return null;
+	try {
+		return JSON.parse(json);
+	} catch {
+		return null;
+	}
+}

frontend/src/routes/(simulator)/components/Canvas2DView.svelte

@@ -3,6 +3,7 @@
 	import { SolarSystem2DRenderer } from '$lib/render/canvas2d/SolarSystem2D';
 	import { simulation } from '$lib/stores/simulation.svelte';
 	import { stations } from '$lib/stores/stations.svelte';
+	import { routing } from '$lib/stores/routing.svelte';
 	import { getBodyPositions, getBodyVelocities, getBodyInfos, getOrbitPoints, getStationPositions } from '$lib/wasm/bridge';
 
 	let canvas: HTMLCanvasElement;
@@ -48,6 +49,16 @@
 					renderer.updateStations(stations.stationPositions, stations.stationNames, stations.visible);
 				}
 
+				// Update route visualization
+				if (routing.route) {
+					renderer.updateRoute(routing.route.legs.map(l => ({
+						from: l.from_station,
+						to: l.to_station,
+					})));
+				} else {
+					renderer.updateRoute([]);
+				}
+
 				if (!orbitsComputed || frameCount % 600 === 0) {
 					computeOrbits();
 				}

frontend/src/routes/(simulator)/components/RoutingPanel.svelte

@@ -0,0 +1,158 @@
+<script lang="ts">
+	import { simulation } from '$lib/stores/simulation.svelte';
+	import { stations } from '$lib/stores/stations.svelte';
+	import { routing } from '$lib/stores/routing.svelte';
+	import { computeRoute } from '$lib/wasm/bridge';
+	import { formatWeeks } from '$lib/utils/format';
+
+	function handleCompute() {
+		if (routing.fromStation === null || routing.toStation === null) {
+			routing.error = 'Select both start and end stations';
+			return;
+		}
+		if (routing.fromStation === routing.toStation) {
+			routing.error = 'Start and end must differ';
+			return;
+		}
+
+		routing.isComputing = true;
+		routing.error = '';
+		routing.route = null;
+
+		// Use setTimeout to let the UI update before blocking computation
+		setTimeout(() => {
+			const result = computeRoute(
+				stations.stationsJson,
+				routing.fromStation!,
+				routing.toStation!,
+				stations.launchVelocityKms,
+				simulation.currentJD,
+				routing.weekWindow,
+			);
+
+			if (result && result.legs.length > 0) {
+				routing.route = result;
+			} else {
+				routing.error = 'No route found. Try increasing velocity or search window.';
+			}
+			routing.isComputing = false;
+		}, 50);
+	}
+
+	const windowOptions = [
+		{ label: '1 year', value: 52 },
+		{ label: '2 years', value: 104 },
+		{ label: '5 years', value: 260 },
+		{ label: '10 years', value: 520 },
+	];
+</script>
+
+<div class="flex flex-col gap-3 p-3 bg-[var(--bg-panel)] rounded-lg border border-white/5">
+	<h3 class="text-xs font-semibold uppercase tracking-wider text-[var(--text-secondary)]">
+		Route Planner
+	</h3>
+
+	<!-- From station -->
+	<div>
+		<label class="text-[10px] text-[var(--text-secondary)] mb-0.5 block">From</label>
+		<select
+			bind:value={routing.fromStation}
+			class="w-full bg-[var(--bg-primary)] text-xs text-[var(--text-primary)] border border-white/10 rounded px-2 py-1.5 [color-scheme:dark]"
+		>
+			<option value={null}>Select station...</option>
+			{#each stations.stationNames as name, i}
+				<option value={i}>{name}</option>
+			{/each}
+		</select>
+	</div>
+
+	<!-- To station -->
+	<div>
+		<label class="text-[10px] text-[var(--text-secondary)] mb-0.5 block">To</label>
+		<select
+			bind:value={routing.toStation}
+			class="w-full bg-[var(--bg-primary)] text-xs text-[var(--text-primary)] border border-white/10 rounded px-2 py-1.5 [color-scheme:dark]"
+		>
+			<option value={null}>Select station...</option>
+			{#each stations.stationNames as name, i}
+				<option value={i}>{name}</option>
+			{/each}
+		</select>
+	</div>
+
+	<!-- Search window -->
+	<div>
+		<label class="text-[10px] text-[var(--text-secondary)] mb-0.5 block">Search Window</label>
+		<div class="flex gap-1">
+			{#each windowOptions as opt}
+				<button
+					onclick={() => { routing.weekWindow = opt.value; }}
+					class="flex-1 px-1 py-0.5 text-[10px] rounded transition-colors {routing.weekWindow === opt.value
+						? 'bg-[var(--accent-blue)] text-white'
+						: 'bg-white/5 text-[var(--text-secondary)] hover:bg-white/10'}"
+				>
+					{opt.label}
+				</button>
+			{/each}
+		</div>
+	</div>
+
+	<!-- Compute button -->
+	<button
+		onclick={handleCompute}
+		disabled={routing.isComputing || routing.fromStation === null || routing.toStation === null}
+		class="w-full py-2 px-3 text-xs font-semibold rounded transition-colors
+			{routing.isComputing
+				? 'bg-[var(--accent-blue)]/50 text-white/50 cursor-wait'
+				: 'bg-[var(--accent-orange)] text-white hover:bg-[var(--accent-orange)]/80 disabled:opacity-30 disabled:cursor-not-allowed'}"
+	>
+		{#if routing.isComputing}
+			Computing route...
+		{:else}
+			Find Optimal Route
+		{/if}
+	</button>
+
+	<!-- Error -->
+	{#if routing.error}
+		<p class="text-[10px] text-red-400">{routing.error}</p>
+	{/if}
+
+	<!-- Route result -->
+	{#if routing.route}
+		<div class="border-t border-white/5 pt-2 mt-1">
+			<div class="flex justify-between items-baseline mb-2">
+				<span class="text-xs font-semibold text-[var(--accent-green)]">Route Found</span>
+				<span class="text-sm font-bold text-[var(--text-primary)]">
+					{formatWeeks(routing.route.total_time_weeks)}
+				</span>
+			</div>
+
+			<div class="text-[10px] text-[var(--text-secondary)] mb-1">
+				Departs week {routing.route.departure_week} &middot; {routing.route.legs.length} leg{routing.route.legs.length !== 1 ? 's' : ''}
+			</div>
+
+			<!-- Leg details -->
+			<div class="flex flex-col gap-1">
+				{#each routing.route.legs as leg, i}
+					<div class="flex items-center gap-1.5 text-[10px]">
+						<span class="w-3 h-3 rounded-full bg-[var(--accent-blue)] flex items-center justify-center text-[8px] text-white font-bold shrink-0">
+							{i + 1}
+						</span>
+						<div class="flex-1 min-w-0">
+							<div class="text-[var(--text-primary)] truncate">
+								{stations.stationNames[leg.from_station]} → {stations.stationNames[leg.to_station]}
+							</div>
+							<div class="text-[var(--text-secondary)]">
+								{formatWeeks(leg.arrival_week - leg.departure_week)} transit
+								{#if leg.wait_weeks > 0}
+									&middot; {formatWeeks(leg.wait_weeks)} wait
+								{/if}
+							</div>
+						</div>
+					</div>
+				{/each}
+			</div>
+		</div>
+	{/if}
+</div>

frontend/src/routes/+page.svelte

@@ -7,6 +7,7 @@
 	import TimeControls from './(simulator)/components/TimeControls.svelte';
 	import ViewToggle from './(simulator)/components/ViewToggle.svelte';
 	import StationPanel from './(simulator)/components/StationPanel.svelte';
+	import RoutingPanel from './(simulator)/components/RoutingPanel.svelte';
 
 	let wasmError = $state('');
 
@@ -58,8 +59,9 @@
 				<Viewport />
 			</div>
 			<!-- Right sidebar -->
-			<aside class="w-64 shrink-0 p-2 bg-[var(--bg-secondary)] border-l border-white/5 overflow-y-auto">
+			<aside class="w-64 shrink-0 p-2 bg-[var(--bg-secondary)] border-l border-white/5 overflow-y-auto flex flex-col gap-2">
 				<StationPanel />
+				<RoutingPanel />
 			</aside>
 		{/if}
 	</main>