feat(frontend): LanderCanvas + App wiring cursor and state to WebSocket

Frontend/src/App.tsx

@@ -1,3 +1,34 @@
-export function App() {
-  return <div style={{ padding: 20 }}>Frontend placeholder</div>;
+import { useGameSocket } from './hooks/useGameSocket';
+import { LanderCanvas } from './LanderCanvas';
+
+// Vite dev server proxies `/ws` → `ws://localhost:5100`. In prod the backend
+// serves the built static files, so same-origin works there too.
+function buildWsUrl(): string {
+  const proto = window.location.protocol === 'https:' ? 'wss:' : 'ws:';
+  return `${proto}//${window.location.host}/ws/game`;
+}
+
+export function App() {
+  const { connected, state, sendCursor } = useGameSocket(buildWsUrl());
+
+  return (
+    <>
+      <LanderCanvas state={state} onCursor={sendCursor} />
+      <StatusBar connected={connected} step={state?.step ?? 0} />
+    </>
+  );
+}
+
+interface StatusBarProps { connected: boolean; step: number; }
+function StatusBar({ connected, step }: StatusBarProps) {
+  return (
+    <div style={{
+      position: 'fixed', top: 8, left: 8, padding: '4px 10px',
+      background: 'rgba(0,0,0,0.5)', borderRadius: 4, fontSize: 12,
+      pointerEvents: 'none',
+    }}>
+      <span style={{ color: connected ? '#5f5' : '#f55' }}>●</span>{' '}
+      {connected ? 'connected' : 'disconnected'} · step {step}
+    </div>
+  );
 }

Frontend/src/LanderCanvas.tsx

@@ -0,0 +1,52 @@
+import { useEffect, useRef } from 'react';
+import type { StateFrame } from './protocol';
+import { renderFrame } from './render';
+import { useAnimationLoop } from './hooks/useAnimationLoop';
+import { useCursorSender } from './hooks/useCursorSender';
+
+export interface LanderCanvasProps {
+  state: StateFrame | null;
+  onCursor: (x: number, y: number) => void;
+}
+
+/**
+ * Full-viewport canvas. Redraws every animation frame reading the latest
+ * `state` prop (no interpolation). Mouse movement is captured on the canvas
+ * and forwarded through `onCursor`.
+ */
+export function LanderCanvas({ state, onCursor }: LanderCanvasProps) {
+  const canvasRef = useRef<HTMLCanvasElement>(null);
+  const stateRef = useRef<StateFrame | null>(state);
+  stateRef.current = state;
+
+  // Keep the canvas's backing store in sync with its CSS size + devicePixelRatio.
+  useEffect(() => {
+    const canvas = canvasRef.current;
+    if (!canvas) return;
+
+    const resize = () => {
+      const dpr = window.devicePixelRatio ?? 1;
+      const rect = canvas.getBoundingClientRect();
+      canvas.width = Math.floor(rect.width * dpr);
+      canvas.height = Math.floor(rect.height * dpr);
+    };
+    resize();
+    window.addEventListener('resize', resize);
+    return () => window.removeEventListener('resize', resize);
+  }, []);
+
+  useAnimationLoop(() => {
+    const canvas = canvasRef.current;
+    if (!canvas) return;
+    renderFrame(canvas, stateRef.current);
+  });
+
+  useCursorSender(canvasRef as React.RefObject<HTMLElement>, onCursor);
+
+  return (
+    <canvas
+      ref={canvasRef}
+      style={{ display: 'block', width: '100vw', height: '100vh', cursor: 'crosshair' }}
+    />
+  );
+}

Frontend/src/hooks/useAnimationLoop.ts

@@ -0,0 +1,17 @@
+import { useEffect, useRef } from 'react';
+
+/** Calls `callback` once per browser frame. Runs while mounted. */
+export function useAnimationLoop(callback: (now: number) => void) {
+  const cbRef = useRef(callback);
+  cbRef.current = callback;
+
+  useEffect(() => {
+    let rafId = 0;
+    const loop = (now: number) => {
+      cbRef.current(now);
+      rafId = requestAnimationFrame(loop);
+    };
+    rafId = requestAnimationFrame(loop);
+    return () => cancelAnimationFrame(rafId);
+  }, []);
+}