Fix parallel nuget build (#10342)

Author: timotheeguerin

.chronus/changes/fix-parallel-nuger-build-2026-3-10-15-44-15.md

@@ -0,0 +1,8 @@
+---
+# Change versionKind to one of: internal, fix, dependencies, feature, deprecation, breaking
+changeKind: internal
+packages:
+  - typespec-vs
+---
+
+Fix parallel nuget build

packages/typespec-vs/scripts/build.js

@@ -6,10 +6,15 @@ import {
   run,
   runDotnet,
 } from "@typespec/internal-build-utils";
+import { mkdtempSync } from "fs";
 import { readFile } from "fs/promises";
+import { tmpdir } from "os";
 import { dirname, join, resolve } from "path";
 import { fileURLToPath } from "url";
 
+// Use a unique NuGet scratch directory to avoid lock contention during parallel builds
+process.env.NUGET_SCRATCH = mkdtempSync(join(tmpdir(), "nuget-scratch-"));
+
 main().catch((e) => {
   console.error(e);
   process.exit(1);