Add controller asset integrity tests

tests/assets.test.mjs

@@ -0,0 +1,42 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+
+import topHud from '../src/assets/controller/top-hud.js';
+import leftStatus from '../src/assets/controller/left-status.js';
+import rightControls from '../src/assets/controller/right-controls.js';
+import cannonRoundel from '../src/assets/controller/cannon-roundel.js';
+import helmFrame from '../src/assets/controller/helm-frame.js';
+import helmKnob from '../src/assets/controller/helm-knob.js';
+
+const assets = {
+  topHud,
+  leftStatus,
+  rightControls,
+  cannonRoundel,
+  helmFrame,
+  helmKnob,
+};
+
+const decodeWebP = (name, dataUrl) => {
+  const match = /^data:image\/webp;base64,([A-Za-z0-9+/=]+)$/.exec(dataUrl);
+  assert.ok(match, `${name} must be a WebP data URL`);
+
+  const bytes = Buffer.from(match[1], 'base64');
+  assert.equal(bytes.subarray(0, 4).toString('ascii'), 'RIFF', `${name} RIFF header`);
+  assert.equal(bytes.subarray(8, 12).toString('ascii'), 'WEBP', `${name} WEBP signature`);
+
+  const declaredSize = bytes.readUInt32LE(4) + 8;
+  assert.equal(
+    bytes.length,
+    declaredSize,
+    `${name} must not be truncated: declared ${declaredSize}, actual ${bytes.length}`,
+  );
+
+  assert.ok(bytes.length > 100, `${name} should contain real image data`);
+};
+
+for (const [name, dataUrl] of Object.entries(assets)) {
+  test(`${name} WebP payload is structurally complete`, () => {
+    decodeWebP(name, dataUrl);
+  });
+}