Bug Report: Next.js 16 Canary SSR Prerender useContext Null Error

Summary

Next.js 16.0.0-canary.7 fails to build due to useContext returning null during SSR prerendering of /_global-error page, even with minimal/no custom error components.

Environment

• Next.js: 16.0.0-canary.7
• React: 19.2.0 (stable)
• Node.js: 20.19.5
• Package Manager: npm 10.9.2
• OS: macOS (Darwin 24.6.0)
• Build Mode: Production (next build --webpack)

Error Message

Error occurred prerendering page "/_global-error". Read more: https://nextjs.org/docs/messages/prerender-error
TypeError: Cannot read properties of null (reading 'useContext')
    at B (.next/server/chunks/3077.js:11:187105) {
  digest: '4119382757'
}
Export encountered an error on /_global-error/page: /_global-error, exiting the build.

Reproduction Steps

1. Create Next.js 16 canary.7 project with React 19.2.0
2. Use next build --webpack (OpenNext Cloudflare adapter requirement)
3. Add custom global-error.tsx with 'use client' and export const dynamic = "force-dynamic"
4. Run build

Minimal Reproduction:

// src/app/global-error.tsx
'use client';

export const dynamic = "force-dynamic";

export default function GlobalError({ error, reset }) {
  return (
    <div>
      <h1>Error</h1>
      <button onClick={reset}>Try Again</button>
    </div>
  );
}

Behavior

• Expected: Build succeeds (global-error should not prerender with force-dynamic)
• Actual: Build fails with useContext null error during prerendering
• Surprising: Error persists even with NO custom global-error.tsx (Next.js default fails)

Investigation

Tested exhaustively:

• ✅ Removed all context providers from custom global-error
• ✅ Used inline styles only (no imported components)
• ✅ Added export const dynamic = "force-dynamic"
• ✅ Deleted custom global-error.tsx entirely (Next.js default still fails)
• ✅ Changed <a> to <button> (eliminate Next.js Link)
• ✅ Removed deprecated config options (swcMinify, eslint)

Result: Error persists in ALL cases

Root Cause

Error occurs in Next.js Link component internals (AppRouterContext is null during SSR):

.next/server/chunks/3077.js:11:187105

This is Next.js framework code, not application code. The error is in how Next.js handles context during static generation of error pages.

Related Issues

• #79427: Similar useContext null with Turbopack in Next.js 15.3.2 (reportedly fixed in 15.5.1-canary.4)
• #65447: Error prerendering /_not-found with pageExtensions
• #55462: Root layout errors not triggering global-error.tsx

Additional Context

Project Type: Large application (2,576+ TypeScript files) Use Case: Cloudflare Workers deployment via OpenNext adapter Migration: From Next.js 14.2.33 → 16.0.0-canary.7

Next.js 16 Breaking Changes Fixed:

• Static runtime config (no conditional exports)
• Client Components with route config (commented out)
• Deprecated config options removed
• 85% migration complete, blocked only by this error

Expected Resolution

Since Issue #79427 indicates a fix exists in later canaries for Next.js 15, likely one of:

1. Fix will appear in Next.js 16.0.0-canary.8+
2. Fix requires React 19.3.0 (not yet released)
3. Different root cause specific to Next.js 16

Workaround Needed

For production deployment with Next.js 16 beta, need way to:

• Disable /_global-error prerendering entirely, OR
• Skip error page static generation, OR
• Use different error boundary approach

Links

• Next.js 16 Beta Blog: https://nextjs.org/blog/next-16-beta
• Related Issue (#79427): https://github.com/vercel/next.js/issues/79427
• Prerender Error Docs: https://nextjs.org/docs/messages/prerender-error