refactor(tanstack-start): reuse TanStack request context

[bgub]

TL;DR

Reuse TanStack Start's existing request context instead of maintaining a second AsyncLocalStorage-backed condition store. Server translation helpers now resolve and memoize conditions directly from TanStack's current Request, so gtMiddleware is optional.

Code Changes

• Remove AsyncLocalConditionStore and its singleton plumbing.
• Resolve server conditions through TanStack's getRequest() and memoize them per request.
• Share the small request cache/config record across package bundle instances.
• Collapse the runtime helpers onto one isomorphic condition lookup.
• Delegate client locale initialization to the existing shared browser condition store.
• Reduce parseLocale() to a deprecated alias for getLocale().
• Retain and deprecate gtMiddleware as a compatibility/eager-warming hook.
• Add focused request isolation, memoization, bundle-sharing, and middleware coverage.

Notes / Flags

• No public API is removed; existing gtMiddleware registrations continue to work.
• Main entry gzip sizes improve from 3.35 kB to 2.94 kB on the client and 3.27 kB to 2.72 kB on the server. The deprecated /server compatibility entry grows from 1.66 kB to 2.47 kB because it now includes direct request resolution.
• Verified with formatting, Oxlint, TypeScript, 29 package tests, and the production package build.

Greptile Summary

Summary

This change replaces the TanStack Start adapter’s async-local request state with conditions resolved from TanStack’s active request, memoized per request, and shared across package instances. It also makes gtMiddleware an optional compatibility hook and uses the shared React browser condition store during client initialization.

Focused execution disproved the relevant failure hypotheses: runtime helpers resolved the active request without middleware, separate requests retained separate locale and enablement values while repeated reads reused the same conditions, and a path locale did not override the cookie locale when locale routing was disabled. The related request-condition and runtime tests passed, and the package typecheck completed successfully.

No defects were found.

Confidence Score: 5/5

The changed TanStack Start request-condition behavior is safe to merge based on the exercised request-resolution, isolation, memoization, and locale-routing paths.

Focused executable coverage exercised the key behavior introduced by this change, while the adjacent changed-module tests and package typecheck also completed successfully. No independently actionable defects remain.

Files Needing Attention: No files need follow-up attention. The exercised implementation paths were packages/tanstack-start/src/functions/requestConditions.ts and packages/tanstack-start/src/functions/runtime.ts.

T-Rex Logs

What T-Rex did

• Ran a focused Vitest test against the changed request-condition and runtime modules.
• Validated runtime helpers read locale and enablement from the mocked active getRequest() without middleware; distinct Request objects produced distinct conditions; repeated reads reused conditions; and locale routing disabled left the cookie locale in effect for /fr/about.
• The focused test passed all three scenarios; the adjacent request-condition and runtime suites passed 10 tests; and the TanStack Start package typecheck completed successfully.
• Validated locale-resolution and per-request condition behavior: runtime.ts resolved locale from the mock, requestConditions.ts produced separate conditions per Request and reused on repeats, and localeRouting=false prevented consulting /fr/about with the locale cookie es.
• Artifacts documenting the validation sources and test results were prepared for review.

_{Ran code and verified through T-Rex}

_{Reviews (1): Last reviewed commit: "refactor(tanstack-start): reuse TanStack..." | Re-trigger Greptile}

[github-actions]

size-limit report 📦

Path	Size
generaltranslation	18.5 KB (0%)
generaltranslation/runtime	15.28 KB (0%)
generaltranslation/id	2.55 KB (0%)
generaltranslation/internal	7.34 KB (0%)
generaltranslation/types	115 B (0%)
generaltranslation/errors	81 B (0%)
@generaltranslation/format	9.92 KB (0%)
@generaltranslation/format/types	89 B (0%)
@generaltranslation/format/internal	880 B (0%)
gt-i18n	11.97 KB (0%)
gt-i18n/types	13 B (0%)
gt-i18n/internal	22.83 KB (0%)
gt-i18n/internal/cookies	228 B (0%)
gt-i18n/internal/string	2.9 KB (0%)
gt-i18n/internal/types	13 B (0%)
@generaltranslation/react-core/pure	26.46 KB (0%)
@generaltranslation/react-core/hooks	21.08 KB (0%)
@generaltranslation/react-core/components	23.52 KB (0%)
@generaltranslation/react-core/components-rsc	26.93 KB (0%)
gt-react (client)	32.86 KB (0%)
gt-react (rsc)	29.47 KB (0%)
gt-react (server)	32.7 KB (0%)
gt-react/macros	8.82 KB (0%)
gt-vue	9.7 KB (0%)
gt-vue (SPA)	19.25 KB (0%)
gt-next (client)	45.05 KB (0%)
gt-next (rsc)	49.32 KB (0%)
gt-next (server)	45.38 KB (0%)
gt-next/config	271.07 KB (0%)
gt-next/server	47.81 KB (0%)
gt-next/middleware	37.84 KB (0%)
gt-next/link	43.92 KB (0%)
gt-next/internal/_dictionary	144 B (0%)
gt-next/internal/_load-translations	144 B (0%)
gt-next/internal/_load-dictionary	144 B (0%)
gt-next/internal/_getLocale	125 B (0%)
gt-next/internal/_getRegion	122 B (0%)
gt-node	23.99 KB (0%)
gt-node/types	219 B (0%)
gt-node/internal	13.4 KB (0%)
gt-tanstack-start (client)	32.36 KB (-0.79% 🔽)
gt-tanstack-start (server)	32.75 KB (-1.05% 🔽)
gt-tanstack-start/server	20.67 KB (+101.65% 🔺)
gt-react-native	31.12 KB (0%)
gt-react-native/plugin	4.72 KB (0%)
gt-react-native/internal	746 B (0%)