Guard package export entrypoints

Author: AbrahamGreenman

scripts/package-runtime-coverage.test.ts

@@ -261,8 +261,11 @@ test("validatePackageRuntimeCoverage requires root export type conditions", asyn
 
   const rootPackageJson = path.join(tempDir, "package.json");
   const packageDir = path.join(tempDir, "packages", "sdk");
+  const cachePackageDir = path.join(tempDir, "packages", "cache");
   await mkdir(packageDir, { recursive: true });
+  await mkdir(cachePackageDir, { recursive: true });
   const sdkPackageJson = path.join(packageDir, "package.json");
+  const cachePackageJson = path.join(cachePackageDir, "package.json");
   await writeFile(
     rootPackageJson,
     JSON.stringify(
@@ -299,10 +302,27 @@ test("validatePackageRuntimeCoverage requires root export type conditions", asyn
       2,
     ),
   );
+  await writeFile(
+    cachePackageJson,
+    JSON.stringify(
+      {
+        name: "@ray/cache-test",
+        type: "module",
+        main: "./dist/index.js",
+        exports: {
+          ".": {
+            default: "./dist/cache.js",
+          },
+        },
+      },
+      null,
+      2,
+    ),
+  );
 
   const summary = await validatePackageRuntimeCoverage({
     cwd: tempDir,
-    packageJsonPaths: [rootPackageJson, sdkPackageJson],
+    packageJsonPaths: [rootPackageJson, sdkPackageJson, cachePackageJson],
   });
   const diagnostics = summary.results.flatMap((result) => result.diagnostics);
 
@@ -321,6 +341,13 @@ test("validatePackageRuntimeCoverage requires root export type conditions", asyn
         diagnostic.packagePath === sdkPackageJson,
     ),
   );
+  assert.ok(
+    diagnostics.some(
+      (diagnostic) =>
+        diagnostic.code === "package_root_export_default_mismatch" &&
+        diagnostic.packagePath === cachePackageJson,
+    ),
+  );
 });
 
 test("validatePackageRuntimeCoverage requires config and Bun cache storage preflight coverage", async (t) => {

scripts/package-runtime-coverage.ts

@@ -758,6 +758,55 @@ function validatePackageExportTypes(
   return diagnostics;
 }
 
+function validatePackageExportMain(
+  packageJsonPath: string,
+  parsedPackage: Record<string, unknown>,
+): PackageRuntimeCoverageDiagnostic[] {
+  const main = parsedPackage.main;
+  const exports = parsedPackage.exports;
+
+  if (typeof main !== "string" || exports === undefined) {
+    return [];
+  }
+
+  const diagnostics: PackageRuntimeCoverageDiagnostic[] = [];
+  if (typeof exports !== "object" || exports === null || Array.isArray(exports)) {
+    diagnostics.push({
+      level: "error",
+      code: "package_exports_must_be_object_for_main",
+      packagePath: packageJsonPath,
+      message:
+        "Package manifests with top-level main must use an object exports map so JavaScript entrypoints can be checked.",
+    });
+    return diagnostics;
+  }
+
+  const rootExport = (exports as Record<string, unknown>)["."];
+  if (typeof rootExport !== "object" || rootExport === null || Array.isArray(rootExport)) {
+    diagnostics.push({
+      level: "error",
+      code: "package_root_export_must_be_object_for_main",
+      packagePath: packageJsonPath,
+      message:
+        'Package manifests with top-level main must expose exports["."] as an object with a matching default condition.',
+    });
+    return diagnostics;
+  }
+
+  const rootExportDefault = (rootExport as Record<string, unknown>).default;
+  if (rootExportDefault !== main) {
+    diagnostics.push({
+      level: "error",
+      code: "package_root_export_default_mismatch",
+      packagePath: packageJsonPath,
+      message:
+        'Package manifests with top-level main must set exports["."].default to the same JavaScript entrypoint so consumers resolve package exports consistently.',
+    });
+  }
+
+  return diagnostics;
+}
+
 function isLocalHealthCurl(line: string): boolean {
   return (
     /\bcurl\b/.test(line) &&
@@ -2940,6 +2989,7 @@ export async function validatePackageRuntimeCoverage(
       const diagnostics = [
         ...validateRootPackageManager(cwd, packageJsonPath, parsedPackage),
         ...validatePackageExportTypes(packageJsonPath, parsedPackage),
+        ...validatePackageExportMain(packageJsonPath, parsedPackage),
         ...validateScripts(packageJsonPath, scripts),
       ];