fix: support Node.js 26.1.0 and 25.9.0

## Problem
- The compatibility matrix covered latest LTS `24.15.0` and older
supported runtime boundaries, but missed newer non-EOL Node lines
`26.1.0` and `25.9.0`.
- Node 26 runtime-deprecates `module.register()` as DEP0205; suppressing
that warning would hide the real migration target.
- `module.registerHooks()` is only safe for tsx's CJS interop path once
Node can re-enter `Module._load` from sync hooks (`24.11.1`, `25.1.0`,
`26.0.0+`). Earlier `registerHooks()` versions keep the async
`module.register()` path.

## Changes
- Add an exact feature gate for the CJS-reload-safe
`module.registerHooks()` boundary, with pinned Node source/PR citations.
- Use sync `registerHooks()` resolve/load hooks on Node versions with
CJS reload support, while preserving async `module.register()` for older
supported Node versions.
- Keep CJS `require()` on tsx's CJS loader path when the global CJS hook
is active, and buffer early IPC dependency messages so watch mode sees
sync-hook loads.
- Update smoke/API/version-sensitive coverage for DEP0205, CJS namespace
shape, `require.cache`, watch reruns, and Node `26.1.0`/`25.9.0`
compatibility.

Author: privatenumber

src/cjs/api/module-resolve-filename/resolve-implicit-extensions.ts

@@ -26,7 +26,7 @@ export const createImplicitResolver = (
 	 */
 	if (isDirectoryPattern.test(request)) {
 		// If directory, can be index.js, index.ts, etc.
-		let joinedPath = path.join(request, 'index.js');
+		let joinedPath = path.join(request, 'index');
 
 		/**
 		 * path.join will remove the './' prefix if it exists
@@ -49,7 +49,7 @@ export const createImplicitResolver = (
 
 		if (nodeError.code === 'MODULE_NOT_FOUND') {
 			try {
-				return nextResolve(`${request}${path.sep}index.js`);
+				return nextResolve(`${request}${path.sep}index`);
 			} catch {}
 		}
 

src/cjs/api/register.ts

@@ -5,6 +5,7 @@ import { loadTsconfig } from '../../utils/tsconfig.js';
 import type { RequiredProperty } from '../../types.js';
 import { urlSearchParamsStringify } from '../../utils/url-search-params-stringify.js';
 import { fileUrlPrefix } from '../../utils/path-utils.js';
+import { activateGlobalCjsLoader } from '../../utils/cjs-loader-state.js';
 import type { LoaderState } from './types.js';
 import { createExtensions } from './module-extensions.js';
 import { createResolveFilename } from './module-resolve-filename/index.js';
@@ -88,6 +89,11 @@ export const register: Register = (
 		tsconfig,
 		options?.namespace,
 	);
+	const unregisterGlobalCjsLoader = (
+		options?.namespace
+			? undefined
+			: activateGlobalCjsLoader()
+	);
 
 	const unregister = () => {
 		if (sourceMapsEnabled === false) {
@@ -103,6 +109,7 @@ export const register: Register = (
 			Module._resolveFilename = originalResolveFilename;
 		}
 		unregisterExtensions();
+		unregisterGlobalCjsLoader?.();
 	};
 
 	if (options?.namespace) {

src/esm/api/register.ts

@@ -2,7 +2,11 @@ import module from 'node:module';
 import { MessageChannel, type MessagePort } from 'node:worker_threads';
 import type { Message } from '../types.js';
 import type { RequiredProperty } from '../../types.js';
+import { isFeatureSupported, moduleRegisterHooksCjsReload } from '../../utils/node-features.js';
 import { interopCjsExports } from '../../cjs/api/module-resolve-filename/interop-cjs-exports.js';
+import { createData } from '../hook/initialize.js';
+import { createLoadSync } from '../hook/load.js';
+import { createResolveSync } from '../hook/resolve.js';
 import { createScopedImport, type ScopedImport } from './scoped-import.js';
 
 export type TsconfigOptions = false | string;
@@ -36,7 +40,12 @@ let cjsInteropApplied = false;
 export const register: Register = (
 	options,
 ) => {
-	if (!module.register) {
+	const supportsRegisterHooks = (
+		typeof module.registerHooks === 'function'
+		&& isFeatureSupported(moduleRegisterHooksCjsReload)
+	);
+
+	if (!module.register && !supportsRegisterHooks) {
 		throw new Error(`This version of Node.js (${process.version}) does not support module.register(). Please upgrade to Node v18.19 or v20.6 and above.`);
 	}
 
@@ -55,6 +64,34 @@ export const register: Register = (
 	const { sourceMapsEnabled } = process;
 	process.setSourceMapsEnabled(true);
 
+	if (supportsRegisterHooks) {
+		const hookData = createData({
+			namespace: options?.namespace,
+			onImport: options?.onImport,
+			tsconfig: options?.tsconfig,
+		});
+		const registeredHooks = module.registerHooks({
+			load: createLoadSync(hookData),
+			resolve: createResolveSync(hookData),
+		});
+
+		const unregister = (async () => {
+			hookData.active = false;
+			registeredHooks.deregister();
+
+			if (sourceMapsEnabled === false) {
+				process.setSourceMapsEnabled(false);
+			}
+		}) as NamespacedUnregister;
+
+		if (options?.namespace) {
+			unregister.import = createScopedImport(options.namespace);
+			unregister.unregister = unregister;
+		}
+
+		return unregister;
+	}
+
 	const { port1, port2 } = new MessageChannel();
 	module.register(
 		// Load new copy of loader so it can be registered multiple times

src/esm/hook/initialize.ts

@@ -6,6 +6,7 @@ import { loadTsconfig } from '../../utils/tsconfig.js';
 
 type Data = InitializationOptions & {
 	active: boolean;
+	onImport?: (url: string) => void;
 	parsedTsconfig: TsconfigResult | undefined;
 };
 
@@ -14,22 +15,39 @@ export const data: Data = {
 	parsedTsconfig: undefined,
 };
 
+export type { Data };
+
+export const createData = (
+	options?: InitializationOptions & {
+		onImport?: (url: string) => void;
+	},
+): Data => {
+	const hookData: Data = {
+		active: true,
+		namespace: options?.namespace,
+		onImport: options?.onImport,
+		parsedTsconfig: undefined,
+		port: options?.port,
+		tsconfig: options?.tsconfig,
+	};
+
+	if (options?.tsconfig !== false) {
+		hookData.parsedTsconfig = loadTsconfig(options?.tsconfig ?? process.env.TSX_TSCONFIG_PATH);
+	}
+
+	return hookData;
+};
+
 export const initialize: InitializeHook = async (
 	options?: InitializationOptions,
 ) => {
 	if (!options) {
 		throw new Error('tsx must be loaded with --import instead of --loader\nThe --loader flag was deprecated in Node v20.6.0 and v18.19.0');
 	}
 
-	data.namespace = options.namespace;
-
-	if (options.tsconfig !== false) {
-		data.parsedTsconfig = loadTsconfig(options.tsconfig ?? process.env.TSX_TSCONFIG_PATH);
-	}
+	Object.assign(data, createData(options));
 
 	if (options.port) {
-		data.port = options.port;
-
 		// Unregister
 		options.port.on('message', (message: string) => {
 			if (message === 'deactivate') {