fix: prefer source plugin-sdk root alias in tests

src/plugin-sdk/root-alias.cjs

@@ -7,6 +7,7 @@ let monolithicSdk = null;
 let diagnosticEventsModule = null;
 const jitiLoaders = new Map();
 const pluginSdkSubpathsCache = new Map();
+const shouldPreferSourceInTests = Boolean(process.env.VITEST) || process.env.NODE_ENV === "test";
 
 function emptyPluginConfigSchema() {
   function error(message) {
@@ -142,7 +143,7 @@ function loadMonolithicSdk() {
   }
 
   const distCandidate = path.resolve(__dirname, "..", "..", "dist", "plugin-sdk", "compat.js");
-  if (fs.existsSync(distCandidate)) {
+  if (!shouldPreferSourceInTests && fs.existsSync(distCandidate)) {
     try {
       monolithicSdk = getJiti(true)(distCandidate);
       return monolithicSdk;
@@ -168,7 +169,7 @@ function loadDiagnosticEventsModule() {
     "infra",
     "diagnostic-events.js",
   );
-  if (fs.existsSync(distCandidate)) {
+  if (!shouldPreferSourceInTests && fs.existsSync(distCandidate)) {
     try {
       diagnosticEventsModule = getJiti(true)(distCandidate);
       return diagnosticEventsModule;

src/plugin-sdk/root-alias.test.ts

@@ -22,6 +22,7 @@ type EmptySchema = {
 
 function loadRootAliasWithStubs(options?: {
   distExists?: boolean;
+  env?: Record<string, string | undefined>;
   monolithicExports?: Record<string | symbol, unknown>;
 }) {
   let createJitiCalls = 0;
@@ -33,7 +34,11 @@ function loadRootAliasWithStubs(options?: {
   };
   const wrapper = vm.runInNewContext(
     `(function (exports, require, module, __filename, __dirname) {${rootAliasSource}\n})`,
-    {},
+    {
+      process: {
+        env: options?.env ?? {},
+      },
+    },
     { filename: rootAliasPath },
   ) as (
     exports: Record<string, unknown>,
@@ -157,6 +162,19 @@ describe("plugin-sdk root alias", () => {
     expect(lazyModule.createJitiOptions.at(-1)?.tryNative).toBe(true);
   });
 
+  it("prefers source loading under vitest even when compat resolves to dist", () => {
+    const lazyModule = loadRootAliasWithStubs({
+      distExists: true,
+      env: { VITEST: "1" },
+      monolithicExports: {
+        slowHelper: () => "loaded",
+      },
+    });
+
+    expect((lazyModule.moduleExports.slowHelper as () => string)()).toBe("loaded");
+    expect(lazyModule.createJitiOptions.at(-1)?.tryNative).toBe(false);
+  });
+
   it("forwards delegateCompactionToRuntime through the compat-backed root alias", () => {
     const delegateCompactionToRuntime = () => "delegated";
     const lazyModule = loadRootAliasWithStubs({