Add React on Rails-specific content to RSC migration docs

[AbanoubGhadban]

Summary

The RSC migration guide series (#2460) is well-written but ~60-70% of the framework-specific content targets Next.js rather than React on Rails. Each document needs React on Rails-specific sections or callouts.

Missing React on Rails Concepts

The following core concepts are barely or never mentioned across all 6 docs:

• Component registration: ReactOnRails.register() vs registerServerComponent() — what changes during migration?
• View helpers: stream_react_component, stream_react_component_with_async_props, rsc_payload_react_component_with_async_props
• ERB integration: "After" migration examples should show both the ERB view and the React component
• Rails controller patterns: How data flows from controllers to RSC components via props
• Shakapacker/Webpack: RSC configuration, bundle analysis with webpack-bundle-analyzer
• Node renderer architecture: React on Rails Pro specifics
• @loadable/component: Migration path from @loadable/component (common in React on Rails) to RSC code splitting

Next.js-Specific Content That Needs React on Rails Equivalents

Next.js Pattern	React on Rails Equivalent Needed
cookies() from next/headers (Auth, Theme, i18n providers)	Controller props from current_user, Rails cookies, i18n-js
app/products/page.jsx file naming	Standalone component files registered with React on Rails
revalidatePath()	Rails controller redirect / Turbo
router.refresh() from next/navigation	React on Rails equivalent
optimizePackageImports in next.config.js	sideEffects: false / Webpack aliases in Shakapacker
NEXT_PUBLIC_ / VITE_ env var prefixes	Shakapacker env var handling
@next/bundle-analyzer	webpack-bundle-analyzer with Shakapacker
next-intl for i18n	i18n-js or Rails I18n passed as props
Single App.jsx root assumption	Multiple registered component roots per page

Per-Document Gaps

1. migrating-to-rsc.md — Doesn't clarify if RSC is Pro-only; no mention of view helpers
2. rsc-component-patterns.md — Zero React on Rails content; "top-down migration" should start from Rails views, not App.jsx
3. rsc-context-and-state.md — Auth/Theme/i18n providers are entirely Next.js-specific
4. rsc-data-fetching.md — Best of the bunch (has async props section), but missing stream_react_component (sync) migration and ERB-side examples
5. rsc-third-party-libs.md — Missing @loadable/component guidance; optimizePackageImports is Next.js-only
6. rsc-troubleshooting.md — Missing React on Rails-specific issues entirely

Recommendation

Each section using Next.js-specific APIs should either:

• Have a parallel "In React on Rails" section showing the equivalent pattern
• Be clearly labeled as "Next.js-specific" with a note about the React on Rails approach
• Or be replaced entirely with React on Rails patterns

Related: #2460