docs: warn about <Outlet /> requirement in layout route files

[dikshit-n]

Summary

Add a documentation warning to the TanStack Start routing guide explaining that layout route files (e.g. posts.tsx) need an <Outlet /> to render child routes.

Problem

Closes #5351

New users following the getting started guide can get stuck when creating nested routes. The development server auto-fills layout route files with a basic component, but without an <Outlet />, child routes silently fail to render. The user sees no error — the dynamic URL just appears to do nothing. This creates a poor first experience.

Solution

Added a [!WARNING] callout directly in the "Creating File Routes" section of docs/start/framework/react/guide/routing.md. The callout:

• Explains that layout routes need <Outlet /> to render children
• Shows a concrete code example with the correct pattern
• Explicitly calls out the symptom (navigating to /posts/123 appears to do nothing)

Changes Made

• docs/start/framework/react/guide/routing.md: Added [!WARNING] callout after the file-routes table, before the "Defining Routes" section

Testing

• Documentation-only change — verified the file parses correctly
• Ran prettier --check on the modified file (documentation format is consistent)

Checklist

• Documentation updated
• No unrelated changes
• No test changes required (this is a docs-only change)

Summary by CodeRabbit

• Documentation
  • Added guidance explaining that layout routes require an <Outlet /> to render child routes.
  • Included an example demonstrating the behavior when <Outlet /> is omitted.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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Plan: Team

Run ID: bf65c363-5627-4594-9f69-3f277713a8c0

📥 Commits

Reviewing files that changed from the base of the PR and between edf0e16 and d146bc4.

📒 Files selected for processing (1)

• docs/start/framework/react/guide/routing.md

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📝 Walkthrough

Walkthrough

The routing guide now explains that layout routes must render <Outlet /> for child routes to appear. It includes a posts.tsx example and documents the behavior when <Outlet /> is omitted.

Changes

Routing documentation

Layer / File(s)	Summary
Document layout route rendering docs/start/framework/react/guide/routing.md	Adds an import and rendering example for <Outlet /> in a layout route. Documents that child routes do not appear when <Outlet /> is omitted.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Merge Risk: ⚪ Minimal · up to b016a

The routing guide now documents the required Outlet usage for layout routes without introducing an outstanding merge risk.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main documentation change: warning that layout routes require .
Description check	✅ Passed	The description explains the problem, solution, affected file, testing, and documentation-only scope. It does not reproduce the repository template headings or release-impact checklist, but the requir…
Linked Issues check	✅ Passed	The PR satisfies issue #5351 by documenting that layout route files require and by explaining the symptom that child routes such as /posts/123 appear not to render.
Out of Scope Changes check	✅ Passed	The changes are limited to the routing guide and directly support the linked issue. No unrelated code or documentation changes are described.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…

Full details: Description check

Explanation

The description explains the problem, solution, affected file, testing, and documentation-only scope. It does not reproduce the repository template headings or release-impact checklist, but the required context is mostly complete.

Full details: Docstring Coverage

Explanation

No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0 files. (1 skipped: 1 unsupported.)

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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