test(traffic): keep the timing test's Vite cache out of the package tree

The traffic timing test starts a Vite server rooted at the package, which
wrote its dependency cache to node_modules/.vite and kept writing after the
server closed. A host running Core's suite then finds files inside Core and
its check refuses them. The server now uses a temporary cache directory,
removed afterwards, and skips dependency discovery, which the SSR-loaded
modules never need.

The HUD place-lookup changelog note credits its PR, #1459.

changelog.d/1459-hud-place-lookups.md

@@ -2,4 +2,4 @@
   looks up place names when no OpenAI key is configured, reverse-geocodes at
   most two points instead of up to four, and looks up again only once the view
   shows a different area, not after every small pan, so a small pan no longer
-  asks OpenAI for a new summary either (samehkhamis, #0000).
+  asks OpenAI for a new summary either (samehkhamis, #1459).

src/data/trafficTiming.test.mjs

@@ -1,5 +1,8 @@
 import assert from 'node:assert/strict';
 import { readLayerSource } from '../testSupport/readLayerSource.mjs';
+import { mkdtempSync, rmSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import path from 'node:path';
 import test from 'node:test';
 import { fileURLToPath } from 'node:url';
 
@@ -136,6 +139,7 @@ test('traffic timing pairs real ordering to the scheduling change and guards re-
   const timeouts = new Map();
   let timerId = 0;
   let server;
+  const cacheDir = mkdtempSync(path.join(tmpdir(), 'gev-traffic-timing-vite-'));
   let trafficLayer;
   let viewer;
 
@@ -159,6 +163,12 @@ test('traffic timing pairs real ordering to the scheduling change and guards re-
     };
     server = await createServer({
       root: fileURLToPath(new URL('../..', import.meta.url)),
+      // Its own optimizer cache, not node_modules/.vite in the package tree:
+      // a host running Core's suite refuses files inside Core.
+      cacheDir,
+      // The test loads modules over SSR; the browser dependency optimizer would
+      // keep writing its cache after the server closes.
+      optimizeDeps: { noDiscovery: true, include: [] },
       configFile: false,
       appType: 'custom',
       logLevel: 'silent',
@@ -328,6 +338,7 @@ test('traffic timing pairs real ordering to the scheduling change and guards re-
     console.warn = originalWarn;
     performance.clearMarks();
     performance.clearMeasures();
+    rmSync(cacheDir, { recursive: true, force: true, maxRetries: 3 });
   }
 });