feat(nextjs): throw missing-env error instead of keyless bootstrap

[djgould]

Description

Part 1 of the keyless→CLI stack. Experiment: promote the CLI keyless flow over SDK keyless mode.

In development, when NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY / CLERK_SECRET_KEY are missing, @clerk/nextjs no longer provisions a keyless application. All three bootstrap entry points (app-router server ClerkProvider, clerkMiddleware, createOrReadKeylessAction) now throw a code=missing_env_keys error directing to:

npx clerk@latest init

The message states the command is non-interactive and requires no Clerk account or login (sandbox agent trials showed agents otherwise route around the CLI or invent placeholder keys). The error surfaces in both the dev server log and the dev error page. Configured keys, claimed keys, and production behavior are unchanged.

Supersedes #9474 (same content, restacked fresh off main).

Checklist

• pnpm test runs as expected.
• pnpm build runs as expected.
• (If applicable) JSDoc comments have been added or updated for any package exports
• (If applicable) Documentation has been updated

Type of change

• 🐛 Bug fix
• 🌟 New feature
• 🔨 Breaking change
• 📖 Refactoring / dependency upgrade / documentation
• other: experiment / RFC

🤖 Generated with Claude Code

[changeset-bot]

🦋 Changeset detected

Latest commit: 1072f9f

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 10 packages

Name	Type
@clerk/backend	Patch
@clerk/nextjs	Minor
@clerk/astro	Patch
@clerk/express	Patch
@clerk/fastify	Patch
@clerk/hono	Patch
@clerk/nuxt	Patch
@clerk/react-router	Patch
@clerk/tanstack-react-start	Patch
@clerk/testing	Patch

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Project	Deployment	Actions	Updated (UTC)
clerk-js-sandbox	Ready	Preview	Aug 18, 2026 6:20pm
swingset	Ready	Preview	Aug 18, 2026 6:20pm

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commit: 1072f9f

[djgould]

Recreated as #9493 to re-base it inside the reordered stack (GitHub blocks base edits on stack members); content unchanged. Successor of #9474.