chore(deps): upgrade Next.js 15 → 16 + React 18 → 19

app/knowledge/guides/[slug]/page.tsx

@@ -155,7 +155,11 @@ const mdxComponents = {
   },
   pre: ({ children }: React.HTMLAttributes<HTMLPreElement>) => {
     // Extract language from code element if present
-    const codeElement = children as React.ReactElement;
+    // React 19 typed ReactElement['props'] as unknown; annotate the shape we read.
+    const codeElement = children as React.ReactElement<{
+      className?: string;
+      children?: React.ReactNode;
+    }>;
     const className = codeElement?.props?.className || '';
     const language = className.replace('language-', '');
 

components/blog/MDXComponents.tsx

@@ -66,7 +66,9 @@ const Img = (
 
   // Extract slug from URL if not provided directly
   useEffect(() => {
-    if (!src) {
+    // React 19 widened ImgHTMLAttributes['src'] to string | Blob; MDX only ever
+    // passes string paths, so narrow before the string operations below.
+    if (!src || typeof src !== 'string') {
       console.info('Image source missing');
       setIsError(true);
       return;

components/blog/ServerMDXContent.tsx

@@ -136,7 +136,9 @@ export default function ServerMDXContent({ content, slug }: ServerMDXContentProp
     img: (imgProps: React.ImgHTMLAttributes<HTMLImageElement>) => {
       const { src, alt } = imgProps;
 
-      if (!src) {
+      // React 19 widened ImgHTMLAttributes['src'] to string | Blob; MDX only ever
+      // passes string paths, so narrow before the string operations below.
+      if (!src || typeof src !== 'string') {
         return <span className="block my-8 p-4 bg-red-50 text-red-500">Image source missing</span>;
       }
 

components/documents/ChatMessageList.tsx

@@ -8,7 +8,7 @@ interface ChatMessageListProps {
   messages: ChatMessage[];
   loading: boolean;
   selectedDocId: string | null;
-  chatEndRef: RefObject<HTMLDivElement>;
+  chatEndRef: RefObject<HTMLDivElement | null>;
 }
 
 export const ChatMessageList = ({

eslint.config.mjs

@@ -0,0 +1,61 @@
+import nextCoreWebVitals from 'eslint-config-next/core-web-vitals';
+import nextTypeScript from 'eslint-config-next/typescript';
+import eslintConfigPrettier from 'eslint-config-prettier';
+
+// ESLint 9 flat config. eslint-config-next 16 ships native flat configs, so we
+// compose them directly instead of wrapping legacy .eslintrc via FlatCompat
+// (which crashes on the react plugin's circular flat-config object). Rule set is
+// carried over verbatim from the previous .eslintrc.json.
+const eslintConfig = [
+  {
+    ignores: [
+      'node_modules/',
+      '.next/',
+      'next-env.d.ts',
+      'dist/',
+      'build/',
+      'coverage/',
+      '*.config.js',
+      '*.config.mjs',
+      'healthcheck.js',
+      'scripts/',
+    ],
+  },
+  ...nextCoreWebVitals,
+  ...nextTypeScript,
+  // Must come after the configs it disables formatting rules from.
+  eslintConfigPrettier,
+  {
+    rules: {
+      '@typescript-eslint/no-unused-vars': [
+        'error',
+        // caughtErrors:'none' preserves the pre-upgrade contract — @typescript-eslint
+        // v8 flipped the default from 'none' to 'all', which would newly flag every
+        // unused `catch (err)` binding. Not a real regression; keep prior behaviour.
+        { argsIgnorePattern: '^_', varsIgnorePattern: '^_', caughtErrors: 'none' },
+      ],
+      '@typescript-eslint/no-explicit-any': 'warn',
+      '@typescript-eslint/explicit-function-return-type': 'off',
+      '@typescript-eslint/explicit-module-boundary-types': 'off',
+      '@typescript-eslint/no-empty-function': 'warn',
+      '@typescript-eslint/no-require-imports': 'off',
+      'no-console': ['error', { allow: ['warn', 'error', 'info'] }],
+      'prefer-const': 'error',
+      'no-var': 'error',
+      'react/no-unescaped-entities': 'off',
+      'react/display-name': 'off',
+      '@next/next/no-img-element': 'warn',
+      // eslint-plugin-react-hooks v6 (bundled with Next 16's eslint-config-next)
+      // adds React-Compiler-era rules that did not exist in the Next 15 config and
+      // flag pre-existing intentional patterns (localStorage hydration, load-on-mount
+      // effects). Adopting them is a dedicated refactor, out of scope for this
+      // framework upgrade — deferred, tracked as follow-up. rules-of-hooks and
+      // exhaustive-deps stay enabled.
+      'react-hooks/set-state-in-effect': 'off',
+      'react-hooks/error-boundaries': 'off',
+      'react-hooks/immutability': 'off',
+    },
+  },
+];
+
+export default eslintConfig;

next-env.d.ts

@@ -1,6 +1,6 @@
 /// <reference types="next" />
 /// <reference types="next/image-types/global" />
-/// <reference path="./.next/types/routes.d.ts" />
+import "./.next/types/routes.d.ts";
 
 // NOTE: This file should not be edited
 // see https://nextjs.org/docs/app/api-reference/config/typescript for more information.

next.config.js

@@ -12,9 +12,8 @@ const nextConfig = {
     ],
   },
   serverExternalPackages: ['onnxruntime-node', '@xenova/transformers', 'sharp'],
-  experimental: {
-    typedRoutes: true,
-  },
+  // typedRoutes graduated from `experimental` to a stable top-level option in Next 16.
+  typedRoutes: true,
   env: {
     NEXT_PUBLIC_DEPLOY_TIME: new Date().toUTCString(),
   },