docs(start): document route and asset base paths

[whizzkid1452]

Summary

• Explain that Vite base prefixes asset URLs while Start router.basepath prefixes application routes and server functions.
• Add examples for matching route and asset prefixes and for serving them from separate paths.
• Add the Base Paths guide to the React and Solid Start navigation.

Closes #4888

Test plan

• pnpm test:docs
• Validate docs/start/config.json with JSON.parse
• Format the changed files with Prettier
• Run affected ESLint, type, unit, and build targets against upstream/main (no affected projects for this documentation-only change)

Summary by CodeRabbit

• Documentation
  • Added React and Solid Base Paths guides explaining how asset prefixes differ from application route and server-function prefixes.
  • Documented matching and separate prefix configurations, server-function prefix behavior, production routing considerations, and ways to verify routes and asset URLs.
  • Added Base Paths navigation entries to the React and Solid framework documentation.

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🧰 Additional context used

📚 Code guidelines (2)

docs/AGENTS.md — auto-discovered
CONTRIBUTING.md — configured

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Advanced

Run ID: 25da2c43-3e84-458d-b422-5a07187ee3d9

📥 Commits

Reviewing files that changed from the base of the PR and between ec92b3a and f1e43d5.

📒 Files selected for processing (2)

• docs/start/framework/react/guide/base-paths.md
• docs/start/framework/solid/guide/base-paths.md

🚧 Files skipped from review as they are similar to previous changes (1)

• docs/start/framework/react/guide/base-paths.md

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📝 Walkthrough

Walkthrough

Adds React and Solid guides for configuring asset and route prefixes. Adds navigation links to both guides.

Changes

Base Paths Documentation

Layer / File(s)	Summary
Base path configuration guide docs/start/framework/react/guide/base-paths.md, docs/start/framework/solid/guide/base-paths.md	Describes Vite asset prefixes, router route prefixes, server-function prefixes, development and production routing, and configuration checks.
Framework navigation integration docs/start/config.json	Adds Base Paths entries to the React and Solid Server & Execution navigation sections.

Priority: ➖ Normal

Estimated code review effort: 1 (Trivial) | ~3 minutes

Change: Other · Severity of issue fixed: Medium

Merge Risk: ⚪ Minimal · up to f1e43

The guides’ navigation and documented base-path behavior align with the runtime; no concrete merge risk is established.

Architecture Summary

Architecture risk: 🔵 Low · up to f1e43

The change affects 1 system.

Changed systems: docs

Architecture concerns
No architecture-level concerns identified.

Review details

Systems and components

• observed — docs (service) was modified; 3 changed files map to changed impact.

Before / after behavior

• observed — Modified behavior in docs/start/config.json: Inserted a new “Base Paths” navigation item (label + to URL) into the react “Server & Execution” sections list directly after “Routing” and before “Execution Model”.
• observed — Modified behavior in docs/start/config.json: Inserted a new “Base Paths” navigation item (label + to URL) into the solid “Server & Execution” sections list directly after “Routing” and before “Execution Model”.
• observed — Modified behavior in docs/start/framework/react/guide/base-paths.md: Added a guide explaining that Vite’s base sets asset URLs while router.basepath sets application-route URLs, and both should be configured in vite.config.ts. Examples show matching /app/ and /app prefixes, where the default serverFns.base of /_serverFn combines with the router base, and root routes with assets under /_ui/. The guide also describes inferred router base paths, development and production request handling, and checks for direct requests, client navigation, asset URLs, and nested-route forwarding.
• observed — Modified behavior in docs/start/framework/solid/guide/base-paths.md: Adds the guide’s base-path concepts and a matching /app/ configuration. It distinguishes Vite asset URLs from Start route URLs, explains that server-function URLs combine router.basepath with the default serverFns.base of /_serverFn, and describes deriving the router base from a path-based Vite base and forwarding requests in production.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the primary change: documenting route and asset base paths for Start.
Description check	✅ Passed	The description explains the documentation changes, motivation, linked issue, and test plan. It does not use the repository template headings or explicitly complete the contribution, AI-understanding,…
Linked Issues check	✅ Passed	Issue #4888 states that the solution requires Vite base and that the issue remains open until this behavior is documented. The React and Solid Start guides document the distinction between Vite `bas…
Out of Scope Changes check	✅ Passed	The reviewed changes are limited to the React and Solid Start base-path guides and their navigation entries. These changes directly support the documentation objective in issue #4888. The evidence sho…
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…

✨ Finishing Touches

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• Create a new PR

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Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@docs/start/framework/react/guide/base-paths.md`:
- Around line 38-46: Update the base-paths documentation around the URL table to
define serverFns.base in the preceding configuration example, or explicitly
document its default value and how it combines with router.basepath for
server-function URLs. Ensure the table’s server-function prefix source is
understandable from the surrounding text.

In `@docs/start/framework/solid/guide/base-paths.md`:
- Around line 1-2: Update the Solid base-paths guide referenced by its
frontmatter so it no longer serves the React guide verbatim. Make the shared
explanation framework-neutral and replace React-specific configuration such as
`@tanstack/react-start/plugin/vite`, `@vitejs/plugin-react`, and viteReact() with
valid Solid-specific examples.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 4dff169e-ef4e-4413-b9ca-3c9c6365acd8

📥 Commits

Reviewing files that changed from the base of the PR and between a76c192 and ec92b3a.

📒 Files selected for processing (3)

• docs/start/config.json
• docs/start/framework/react/guide/base-paths.md
• docs/start/framework/solid/guide/base-paths.md