@@ -56,7 +56,7 @@ function readOrchestrionPluginGraphSources(): string[] {
   const entrySource = fs.readFileSync(pluginEntry, 'utf8');
   return [
     entrySource,
-    ...[...entrySource.matchAll(/require\('(\.\.?\/[^']+)'\)/g)].map(([, specifier]) =>
+    ...[...entrySource.matchAll(/require\(['"](\.\.?\/[^'"]+)['"]\)/g)].map(([, specifier]) =>
       fs.readFileSync(path.resolve(path.dirname(pluginEntry), specifier), 'utf8'),
     ),
   ];
 
@@ -12,7 +12,7 @@
   "scripts": {
     "build": "pnpm run build:transpile && pnpm run build:types",
     "build:dev": "pnpm run build",
-    "build:transpile": "rollup -c rollup.npm.config.mjs",
+    "build:transpile": "rolldown -c rollup.npm.config.mjs",
     "build:types": "tsc -p tsconfig.types.json",
     "clean": "rimraf -g suites/**/node_modules suites/**/tmp_* && pnpm run clean:script",
     "clean:script": "node scripts/clean.js",
 
@@ -0,0 +1,14 @@
+import * as Sentry from '@sentry/node';
+
+// `Sentry.init()` synchronously calls `registerDiagnosticsChannelInjection()`, which reaches the
+// vendored orchestrion transformer. That chain is split so a bundler can tree-shake it (see
+// `makeCjsExportsSplitPlugin` in server-utils' rollup config); this asserts the split degrades to
+// "no channel injection" rather than throwing when the bundler drops it.
+Sentry.init({
+  dsn: 'https://public@dsn.ingest.sentry.io/1337',
+  tracesSampleRate: 0,
+  autoSessionTracking: false,
+});
+
+// eslint-disable-next-line no-console
+console.log(`SENTRY_NODE_INITIALIZED client=${Boolean(Sentry.getClient())}`);
@@ -32,4 +32,34 @@ describe('esbuild bundling', () => {
       rmSync(outDir, { recursive: true, force: true });
     }
   });
+
+  test('@sentry/node survives init() when bundled to ESM with tree-shaking', async () => {
+    const outDir = mkdtempSync(join(tmpdir(), 'sentry-esbuild-esm-'));
+    const outfile = join(outDir, 'bundle.mjs');
+
+    try {
+      await build({
+        entryPoints: [join(__dirname, 'app-init.ts')],
+        outfile,
+        platform: 'node',
+        format: 'esm',
+        bundle: true,
+        // `@sentry/server-utils` is `sideEffects: false`, so this is where a bundler is free to
+        // drop the vendored orchestrion transformer.
+        treeShaking: true,
+        logLevel: 'silent',
+      });
+
+      const result = spawnSync('node', [outfile], { encoding: 'utf-8' });
+
+      // Dropping the transformer must not take `init()` with it: reading a tree-shaken CJS
+      // container has to yield `undefined`, not throw on destructuring or on a call.
+      expect(result.stderr).not.toContain('Cannot destructure');
+      expect(result.stderr).not.toContain('is not a function');
+      expect(result.status).toBe(0);
+      expect(result.stdout).toContain('SENTRY_NODE_INITIALIZED client=true');
+    } finally {
+      rmSync(outDir, { recursive: true, force: true });
+    }
+  });
 });
@@ -1,56 +1,50 @@
 /**
- * Rollup config docs: https://rollupjs.org/guide/en/#big-list-of-options
+ * Rolldown config docs: https://rolldown.rs/reference/config-options
  */
 
-import { builtinModules } from 'module';
+import * as fs from 'fs';
+import * as path from 'path';
 
 import deepMerge from 'deepmerge';
 
 import {
+  makeBannerOptions,
   makeBrowserBuildPlugin,
-  makeCommonJSPlugin,
-  makeEsbuildPlugin,
   makeIsDebugBuildPlugin,
-  makeLicensePlugin,
-  makeNodeResolvePlugin,
+  makeMinifierOptions,
   makeRrwebBuildPlugin,
   makeSetSDKSourcePlugin,
-  makeTerserPlugin,
 } from './plugins/index.mjs';
-import { mergePlugins } from './utils.mjs';
+import { getNodeBuiltIns, mergePlugins, treeShakePreset } from './utils.mjs';
 import { makeProductionReplacePlugin } from './plugins/npmPlugins.mjs';
 
 const BUNDLE_VARIANTS = ['.js', '.min.js', '.debug.min.js'];
 
+const packageDotJSON = JSON.parse(fs.readFileSync(path.resolve(process.cwd(), './package.json'), { encoding: 'utf8' }));
+
 export function makeBaseBundleConfig(options) {
-  const { bundleType, entrypoints, licenseTitle, outputFileBase, packageSpecificConfig, esbuild } = options;
+  const { bundleType, entrypoints, licenseTitle, outputFileBase, packageSpecificConfig } = options;
 
-  const nodeResolvePlugin = makeNodeResolvePlugin();
-  const transpilePlugin = makeEsbuildPlugin(esbuild);
   const markAsBrowserBuildPlugin = makeBrowserBuildPlugin(true);
-  const licensePlugin = makeLicensePlugin(licenseTitle);
+  const banner = makeBannerOptions(licenseTitle, packageDotJSON.version);
   const rrwebBuildPlugin = makeRrwebBuildPlugin({
     excludeIframe: false,
     excludeShadowDom: false,
   });
   const productionReplacePlugin = makeProductionReplacePlugin();
 
-  // The `commonjs` plugin is the `esModuleInterop` of the bundling world. When used with `transformMixedEsModules`, it
-  // will include all dependencies, imported or required, in the final bundle. (Without it, CJS modules aren't included
-  // at all, and without `transformMixedEsModules`, they're only included if they're imported, not if they're required.)
-  const commonJSPlugin = makeCommonJSPlugin({ transformMixedEsModules: true });
-
   // used by `@sentry/browser`
   const standAloneBundleConfig = {
     output: {
+      banner,
       format: 'iife',
       name: 'Sentry',
       intro: () => {
         return 'exports = window.Sentry || {};';
       },
     },
     context: 'window',
-    plugins: [rrwebBuildPlugin, markAsBrowserBuildPlugin, licensePlugin],
+    plugins: [rrwebBuildPlugin, markAsBrowserBuildPlugin],
   };
 
   // used by `@sentry/wasm` & pluggable integrations from core/browser (bundles which need to be combined with a stand-alone SDK bundle)
@@ -61,7 +55,7 @@ export function makeBaseBundleConfig(options) {
       format: 'cjs',
 
       // code to add before the CJS wrapper
-      banner: '(function (__window) {',
+      banner: `${banner}\n(function (__window) {`,
 
       // code to add just inside the CJS wrapper, before any of the wrapped code
       intro: 'var exports = {};',
@@ -84,30 +78,41 @@ export function makeBaseBundleConfig(options) {
       // code to add after the CJS wrapper
       footer: '}(window));',
     },
-    plugins: [rrwebBuildPlugin, markAsBrowserBuildPlugin, licensePlugin],
+    plugins: [rrwebBuildPlugin, markAsBrowserBuildPlugin],
   };
 
   const workerBundleConfig = {
     output: {
+      banner,
       format: 'esm',
+      minify: makeMinifierOptions(),
     },
-    plugins: [commonJSPlugin, makeTerserPlugin(), licensePlugin],
     // Don't bundle any of Node's core modules
-    external: builtinModules,
+    external: getNodeBuiltIns(),
   };
 
   const awsLambdaExtensionBundleConfig = {
     output: {
       format: 'esm',
+      minify: makeMinifierOptions(),
     },
-    plugins: [commonJSPlugin, makeIsDebugBuildPlugin(true), makeTerserPlugin()],
+    plugins: [makeIsDebugBuildPlugin(true)],
     // Don't bundle any of Node's core modules
-    external: builtinModules,
+    external: getNodeBuiltIns(),
   };
 
   // used by all bundles
   const sharedBundleConfig = {
     input: entrypoints,
+
+    // Point at the package's tsconfig so rolldown picks up its TypeScript & JSX settings.
+    tsconfig: path.resolve(process.cwd(), './tsconfig.json'),
+
+    // ES2020 is our floor: keeps `?.`/`??` native and downlevels everything newer.
+    transform: {
+      target: 'es2020',
+    },
+
     output: {
       // a file extension will be added to this base value when we specify either a minified or non-minified build
       entryFileNames: outputFileBase,
@@ -116,8 +121,8 @@ export function makeBaseBundleConfig(options) {
       strict: false,
       esModule: false,
     },
-    plugins: [productionReplacePlugin, transpilePlugin, nodeResolvePlugin],
-    treeshake: 'smallest',
+    plugins: [productionReplacePlugin],
+    treeshake: treeShakePreset('smallest'),
   };
 
   const bundleTypeConfigMap = {
@@ -147,7 +152,7 @@ export function makeBundleConfigVariants(baseConfig, options = {}) {
 
   const includeDebuggingPlugin = makeIsDebugBuildPlugin(true);
   const stripDebuggingPlugin = makeIsDebugBuildPlugin(false);
-  const terserPlugin = makeTerserPlugin();
+  const minify = makeMinifierOptions();
   const setSdkSourcePlugin = makeSetSDKSourcePlugin('cdn');
 
   // The additional options to use for each variant we're going to create.
@@ -162,15 +167,17 @@ export function makeBundleConfigVariants(baseConfig, options = {}) {
     '.min.js': {
       output: {
         entryFileNames: chunkInfo => `${baseConfig.output.entryFileNames(chunkInfo)}.min.js`,
+        minify,
       },
-      plugins: [stripDebuggingPlugin, setSdkSourcePlugin, terserPlugin],
+      plugins: [stripDebuggingPlugin, setSdkSourcePlugin],
     },
 
     '.debug.min.js': {
       output: {
         entryFileNames: chunkInfo => `${baseConfig.output.entryFileNames(chunkInfo)}.debug.min.js`,
+        minify,
       },
-      plugins: [includeDebuggingPlugin, setSdkSourcePlugin, terserPlugin],
+      plugins: [includeDebuggingPlugin, setSdkSourcePlugin],
     },
   };
 
 
@@ -4,4 +4,4 @@ export { plugins };
 
 export * from './bundleHelpers.mjs';
 export * from './npmHelpers.mjs';
-export { insertAt } from './utils.mjs';
+export { insertAt, treeShakePreset } from './utils.mjs';
@@ -1,27 +1,25 @@
 // @ts-check
 
 /**
- * Rollup config docs: https://rollupjs.org/guide/en/#big-list-of-options
+ * Rolldown config docs: https://rolldown.rs/reference/config-options
  */
 
 import * as fs from 'fs';
-import { builtinModules, isBuiltin } from 'module';
+import { isBuiltin } from 'module';
 import * as path from 'path';
 import { fileURLToPath } from 'url';
 
 import deepMerge from 'deepmerge';
 
-import { defineConfig } from 'rollup';
+import { defineConfig } from 'rolldown';
 import {
   makeDebugBuildStatementReplacePlugin,
-  makeEsbuildPlugin,
   makeEsmCjsReplacePlugin,
-  makeNodeResolvePlugin,
   makeProductionReplacePlugin,
   makeRrwebBuildPlugin,
 } from './plugins/index.mjs';
 import { makePackageNodeEsm } from './plugins/make-esm-plugin.mjs';
-import { mergeExternals, mergePlugins } from './utils.mjs';
+import { getNodeBuiltIns, mergeExternals, mergePlugins } from './utils.mjs';
 
 const __dirname = path.dirname(fileURLToPath(import.meta.url));
 
@@ -97,20 +95,17 @@ export function makeBaseNPMConfig(options = {}) {
     entrypoints = ['src/index.ts'],
     hasBundles = false,
     packageSpecificConfig = {},
-    esbuild = {},
     bundledBuiltins = [],
   } = options;
 
-  const nodeResolvePlugin = makeNodeResolvePlugin();
-  const transpilePlugin = makeEsbuildPlugin(esbuild);
   const debugBuildStatementReplacePlugin = makeDebugBuildStatementReplacePlugin();
   const rrwebBuildPlugin = makeRrwebBuildPlugin({
     excludeShadowDom: undefined,
     excludeIframe: undefined,
   });
 
   const deps = [
-    ...builtinModules.filter(m => !bundledBuiltins.includes(m)),
+    ...getNodeBuiltIns(bundledBuiltins),
     ...Object.keys(packageDotJSON.dependencies || {}),
     ...Object.keys(packageDotJSON.peerDependencies || {}),
     ...Object.keys(packageDotJSON.optionalDependencies || {}),
@@ -119,6 +114,31 @@ export function makeBaseNPMConfig(options = {}) {
   const defaultBaseConfig = {
     input: entrypoints,
 
+    // Point at the package's tsconfig so rolldown picks up its TypeScript & JSX settings.
+    tsconfig: path.resolve(process.cwd(), './tsconfig.json'),
+
+    // NOTE: we deliberately leave `platform` unset so rolldown infers it from the output format
+    // ('node' for cjs, 'browser' for everything else). Every explicit value breaks something:
+    // 'node' injects `import "node:module"` into each runtime chunk, which webpack rejects for
+    // browser targets; 'neutral' rewrites `import.meta` to `{}`, so `createRequire(import.meta.url)`
+    // gets `undefined`. Node-only packages that need the node platform for both halves set it
+    // themselves (see server-utils and bundler-plugins).
+
+    // ES2020 is our floor: keeps `?.`/`??` native and downlevels everything newer. Packages that
+    // need more (e.g. top-level await) raise it through `packageSpecificConfig`.
+    transform: {
+      target: 'es2020',
+
+      // The inferred 'browser' platform defines `process.env.NODE_ENV`, which folds every
+      // `process.env.NODE_ENV !== 'development'` guard to a constant and lets DCE delete the
+      // branch behind it. That silently dropped the orchestrion and source-map plugins from the
+      // vite integrations' ESM output while the CJS half kept them. Mapping it to itself keeps
+      // the runtime lookup, so the guard is evaluated by the consumer as it always was.
+      define: {
+        'process.env.NODE_ENV': 'process.env.NODE_ENV',
+      },
+    },
+
     output: {
       // an appropriately-named directory will be added to this base value when we specify either a cjs or esm build
       dir: hasBundles ? 'build/npm' : 'build',
@@ -130,6 +150,7 @@ export function makeBaseNPMConfig(options = {}) {
 
       // output individual files rather than one big bundle
       preserveModules: true,
+      preserveModulesRoot: 'src',
 
       // Don't hoist imports into entrypoints
       // should be ignored when `preserveModules` is used,
@@ -139,8 +160,6 @@ export function makeBaseNPMConfig(options = {}) {
       // Allow wrappers or helper functions generated by rollup to use any ES2015 features
       generatedCode: {
         preset: 'es2015',
-        // With arrow functions, Node can't see `export *` exports when ESM code imports our CJS files.
-        arrowFunctions: false,
       },
 
       // don't add `"use strict"` to the top of cjs files
@@ -154,19 +173,17 @@ export function makeBaseNPMConfig(options = {}) {
       //       get: () => are.great,
       //     });
       externalLiveBindings: false,
-
-      // Don't call `Object.freeze` on the results of `import * as someModule from '...'`
-      // (We don't need it, so why waste the bytes?)
-      freeze: false,
-
-      // Assume externals are ESM-shaped (`__esModule` + `.default`), which our own `@sentry/*`
-      // packages satisfy via `esModule: 'if-default-prop'`. This keeps `import * as x` a live
-      // reference to the real module rather than an `_interopNamespace` copy — instrumentation code
-      // relies on that to monkey-patch modules like `fs` in place. Packages that pull in bare-CJS
-      // third-party deps (no `.default`) override this per-module (see server-utils).
-      interop: 'esModule',
     },
 
+    // NOTE: rolldown has no equivalent of rollup's `output.interop`. In the CJS build it wraps
+    // namespace imports of externals as `x = __toESM(require('x'))`, and `__toESM` returns a copy
+    // whose properties are getter-only forwarders. Reads pass through to the real module but writes
+    // do not, so code that monkey-patches a module in place has to default-import it (`import x
+    // from 'x'`, whose `.default` is the live `require()` result) rather than namespace-import it.
+    // Rolldown errors on a statically visible `ns.foo = ...` (ASSIGN_TO_IMPORT), but it cannot see a
+    // write made through a helper, and that one fails silently. See
+    // `packages/node/src/integrations/fs/vendored/instrumentation.ts`.
+
     treeshake: {
       moduleSideEffects: (id, external) => {
         if (external === false && ignoreSideEffects.test(id)) {
@@ -186,7 +203,7 @@ export function makeBaseNPMConfig(options = {}) {
       },
     },
 
-    plugins: [nodeResolvePlugin, transpilePlugin, debugBuildStatementReplacePlugin, rrwebBuildPlugin],
+    plugins: [debugBuildStatementReplacePlugin, rrwebBuildPlugin],
 
     // don't include imported modules from outside the package in the final output
     // also treat subpath exports (e.g. `@sentry/core/browser`) as external
@@ -248,8 +265,7 @@ export function makeNPMConfigVariants(baseConfig, options = {}) {
   }
 
   return variantSpecificConfigs.map(variant =>
-    // Plugin arrays must be merged in the right order or the build silently misbehaves
-    // (e.g. esbuild strips dev-mode marker comments before the replace plugin can act).
+    // Plugin arrays must be merged in the right order or the build silently misbehaves.
     deepMerge(baseConfig, variant, {
       customMerge: key => (key === 'plugins' ? mergePlugins : undefined),
     }),