fix(core): isolate Vite cache for integration test servers

packages/core/tests/integration/client/concurrent-servers.test.ts

@@ -15,6 +15,9 @@
  * its own copied fixture root) both succeed.
  */
 
+import { existsSync, readdirSync } from "node:fs";
+import { join } from "node:path";
+
 import { describe, it, expect, afterAll } from "vitest";
 
 import type { TestServerContext } from "../server.js";
@@ -45,8 +48,17 @@ describe("Concurrent dev servers (#1604)", () => {
 		// Start both concurrently so they race for the (previously shared) lock.
 		const [a, b] = await Promise.all([startTracked(PORT_A), startTracked(PORT_B)]);
 
-		// Distinct roots -- the fix gives each server its own copied fixture.
-		expect(a.cwd).not.toBe(b.cwd);
+		// Vite must write optimizer output into each server's private cache root,
+		// not follow the shared node_modules symlink to one physical cache.
+		for (const cwd of [a.cwd, b.cwd]) {
+			const cacheDir = join(cwd, ".vite-cache");
+			expect(existsSync(cacheDir), `${cacheDir} was never created`).toBe(true);
+			const output = readdirSync(cacheDir, { recursive: true, withFileTypes: true });
+			expect(
+				output.some((entry) => entry.isFile()),
+				`${cacheDir} contains no Vite cache output`,
+			).toBe(true);
+		}
 
 		// Both must actually serve their independently seeded content.
 		const [collectionsA, collectionsB] = await Promise.all([
@@ -58,5 +70,5 @@ describe("Concurrent dev servers (#1604)", () => {
 			expect(slugs).toContain("posts");
 			expect(slugs).toContain("pages");
 		}
-	});
+	}, 120_000);
 });

packages/core/tests/integration/fixture/astro.config.mjs

@@ -13,6 +13,7 @@ import { sqlite } from "emdash/db";
 
 const dbUrl = process.env.EMDASH_TEST_DB || "file:./test.db";
 const uploadsDir = process.env.EMDASH_TEST_UPLOADS || "./uploads";
+const viteCacheDir = process.env.EMDASH_TEST_VITE_CACHE || undefined;
 const _rawMaxUploadSize = process.env.EMDASH_MAX_UPLOAD_SIZE
 	? parseInt(process.env.EMDASH_MAX_UPLOAD_SIZE, 10)
 	: undefined;
@@ -40,6 +41,7 @@ export default defineConfig({
 	},
 	devToolbar: { enabled: false },
 	vite: {
+		cacheDir: viteCacheDir,
 		server: {
 			fs: {
 				// When running from a temp dir, node_modules is symlinked back to the

packages/core/tests/integration/server.ts

@@ -162,6 +162,7 @@ export async function createTestServer(options: TestServerOptions): Promise<Test
 	});
 	const dbPath = join(workDir, "test.db");
 	const uploadsDir = join(workDir, "uploads");
+	const viteCacheDir = join(workDir, ".vite-cache");
 	mkdirSync(uploadsDir, { recursive: true });
 
 	// Borrow the donor node_modules via symlink (resolution still hits real
@@ -181,6 +182,7 @@ export async function createTestServer(options: TestServerOptions): Promise<Test
 			ASTRO_DEV_BACKGROUND: "1",
 			EMDASH_TEST_DB: `file:${dbPath}`,
 			EMDASH_TEST_UPLOADS: uploadsDir,
+			EMDASH_TEST_VITE_CACHE: viteCacheDir,
 			...options.env,
 		},
 		stdio: "pipe",