Refactor SSR router state to use AsyncLocalStorage

[natew]

Summary

Currently, the router uses module-level state that persists across SSR requests. We work around this by calling globalThis['__vxrnresetState']?.() before each render, but this doesn't handle concurrent requests safely.

This issue tracks refactoring to use AsyncLocalStorage for proper per-request state isolation.

Current Implementation

Problem: 14+ module-level variables in router.ts persist across requests:

• initialized, routeNode, rootComponent
• Navigation state: initialState, rootState, nextState, routeInfo
• navigationRef, navigationRefSubscription
• 3 subscriber Set collections
• linkingConfig

Current workaround in oneServe.ts:184:

// Reset router state for each SSR request to ensure correct routing
// TODO: Consider using AsyncLocalStorage to isolate router state per request
// instead of using global reset, for better concurrency handling
globalThis['__vxrnresetState']?.()

Proposed Solution

Use AsyncLocalStorage (already used successfully in one-server-only.tsx for per-request headers).

1. Create routerAsyncLocalStore.ts

import { AsyncLocalStorage } from 'node:async_hooks'

interface RouterContextState {
  initialized: boolean
  routeNode: RouteNode | null
  rootState: NavigationState | undefined
  nextState: ResultState | undefined
  routeInfo: UrlObject | undefined
  navigationRef: NavigationContainerRef<any> | null
  // ... other state
}

export const ROUTER_CONTEXT_STORE = new AsyncLocalStorage<RouterContextState>()

export function getRouterContext() {
  return ROUTER_CONTEXT_STORE.getStore()
}

export function runWithRouterContext<T>(fn: () => T): T {
  return ROUTER_CONTEXT_STORE.run(createInitialContext(), fn)
}

2. Update router.ts

Replace module-level variable access with context getters.

3. Wrap SSR rendering in oneServe.ts

const response = await runWithRouterContext(async () => {
  const rendered = await (await getRender())({ ... })
  return new Response(rendered, { headers, status })
})

Benefits

• True request isolation (no state leakage between concurrent requests)
• Concurrency safe for parallel SSR requests
• Automatic cleanup per request
• Removes manual reset workaround
• Follows existing pattern in codebase (one-server-only.tsx)

Considerations

• Keep cacheable data (preloadingLoader, cssInjectFunctions) at module level for performance
• Need fallback for Vercel Lambda (doesn't support getStore() - but existing code has fallback patterns)
• Only applies to SSR path, not client-side

Files to Modify

• packages/one/src/router/router.ts - Move state to AsyncLocalStorage
• packages/one/src/router/useInitializeOneRouter.ts - Update initialization
• packages/one/src/router/linkingConfig.ts - Move linkingConfig to context
• packages/one/src/server/oneServe.ts - Wrap rendering in context
• packages/one/src/cli/buildPage.ts - Wrap SSG rendering in context