diff --git a/playwright.ui.config.ts b/playwright.ui.config.ts
index d2ab7c67..dfab4155 100644
--- a/playwright.ui.config.ts
+++ b/playwright.ui.config.ts
@@ -1,8 +1,24 @@
+import { randomInt } from "node:crypto";
 import { defineConfig } from "@playwright/test";
 
-const port = Number(process.env.UI_TEST_PORT || 3107);
-if (!Number.isInteger(port) || port < 1024 || port > 65535)
-	throw Error("Invalid UI_TEST_PORT");
+// The fixture server binds a loopback port. The CI runner packs several jobs
+// onto the shared host network (capacity > 1), so a fixed port makes concurrent
+// runs fight over the bind: one wins, the other's browser then gets
+// "connection refused". Pick one random high port for the whole run and pass it
+// to every worker through the environment, unless a port is pinned explicitly
+// (e.g. a developer reusing a manually started fixture server).
+function fixturePort() {
+	const requested = Number(process.env.UI_TEST_PORT);
+	if (Number.isInteger(requested) && requested >= 1024 && requested <= 65535)
+		return requested;
+	const shared = Number(process.env.PW_UI_TEST_PORT);
+	if (Number.isInteger(shared) && shared >= 1024 && shared <= 65535)
+		return shared;
+	const port = randomInt(30000, 50000);
+	process.env.PW_UI_TEST_PORT = String(port);
+	return port;
+}
+const port = fixturePort();
 const baseURL = `http://127.0.0.1:${port}`;
 export default defineConfig({
 	testDir: "./e2e/ui",
@@ -65,7 +81,7 @@ export default defineConfig({
 		command: "node e2e/ui/fixture-server.mjs",
 		url: `${baseURL}/health`,
 		timeout: 120000,
-		reuseExistingServer: true,
+		reuseExistingServer: !process.env.CI,
 		env: { UI_TEST_PORT: String(port) },
 	},
 });