try this

package.json

@@ -25,10 +25,9 @@
     "release:check": "changeset status --verbose --since=origin/main",
     "release:publish": "pnpm install && pnpm build && changeset publish",
     "release:version": "changeset version && pnpm install --lockfile-only && pnpm run changelog:generate",
-    "pretest": "ANVIL_PORT=8556 tsx test-setup/startAnvil.ts & wait-on tcp:8556",
-    "test": "pnpm run --recursive test",
-    "pretest:ci": "pnpm run pretest",
-    "test:ci": "pnpm run --recursive test:ci",
+    "test": "pnpm run test:start-anvil & wait-on tcp:8556 && pnpm run --recursive test",
+    "test:ci": "pnpm run test:start-anvil & wait-on tcp:8556 && pnpm run --recursive test:ci",
+    "test:start-anvil": "tsx test-setup/startAnvil.ts",
     "type-bench": "pnpm --filter ./test/ts-benchmarks bench",
     "type-stats-repo": "attest stats packages/*",
     "vercel:prepare": "(forge --version || pnpm foundryup) && ln -sf /vercel/.foundry/bin/* node_modules/.bin/ && forge --version"

test-setup/common.ts

@@ -1,7 +1,7 @@
 import { createTestClient, http } from "viem";
 
-export const anvilHost = process.env.ANVIL_HOST ?? "127.0.0.1";
-export const anvilPort = process.env.ANVIL_PORT ?? "8556";
+export const anvilHost = process.env.ANVIL_HOST || "127.0.0.1";
+export const anvilPort = Number(process.env.ANVIL_PORT) || 8556;
 
 // ID of the current test worker. Used by the `@viem/anvil` proxy server.
 export const poolId = Number(process.env.VITEST_POOL_ID ?? 1);

test-setup/startAnvil.ts

@@ -13,10 +13,7 @@ await execa("pnpm", ["run", "build"], {
 });
 
 console.log("starting anvil proxy");
-await startAnvilProxy({
-  host: anvilHost,
-  port: Number(anvilPort),
-});
+await startAnvilProxy({ host: anvilHost, port: anvilPort });
 
 // ensure anvil dies
 process.on("SIGINT", () => process.exit());