ENG-9553: prepend frontend_path to RouterData.url and RouterData.page.raw_path

[masenf]

If a frontend path is configured for the app, the framework must prepend it to the reported path, which only includes the internal route path.

[linear]

ENG-9553

[codspeed-hq]

Merging this PR will not alter performance

✅ 24 untouched benchmarks

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_{Comparing masenf/router-url-frontend-path (e8f5945) with main (5d65aa9)}

[greptile-apps]

Greptile Summary

This PR ensures that RouterData.url and PageData.raw_path both include the configured frontend_path prefix. Previously, Next.js asPath (stored as RouteVar.ORIGIN) only carried the app-relative path, so state consumers reading router.url.path or router.page.raw_path saw a path that did not match what the browser displayed.

• PageData.from_router_data now wraps the raw asPath with get_config().prepend_frontend_path(...) before assigning it to raw_path (and consequently full_raw_path).
• RouterData.from_router_data applies the same transformation when building the full ReflexURL, so router.url and router.url.path reflect the browser-visible URL.
• A new integration test (test_router_includes_frontend_path) verifies the fix across index, static, and dynamic routes for all prefix variants.

Confidence Score: 4/5

The change is safe to merge; both call sites are straightforward and the fix is well-covered by a new parameterised integration test.

The core logic is correct: Next.js strips basePath from asPath before sending it to the backend, so prepending frontend_path server-side is the right fix. The only observations are minor — get_config() is called twice per request where once would suffice, and the test has a redundant regex assertion that cannot catch anything the exact-value check misses.

No files require special attention; both changed files are straightforward.

Important Files Changed

Filename	Overview
reflex/istate/data.py	Prepends frontend_path to raw_path in PageData and to the URL in RouterData; get_config() is called twice per request
tests/integration/tests_playwright/test_frontend_path.py	Adds _router_info() UI helper and test_router_includes_frontend_path test; contains a redundant regex assertion before an exact-value check on #router-url

Sequence Diagram

sequenceDiagram
    participant Browser
    participant Frontend as Next.js Frontend
    participant Backend as Reflex Backend
    participant RouterData as RouterData.from_router_data()

    Browser->>Frontend: Navigate to /prefix/dynamic/42
    Note over Frontend: basePath="/prefix"<br/>router.asPath="/dynamic/42"
    Frontend->>Backend: "WebSocket: {asPath: "/dynamic/42", pathname: "/dynamic/[page_id]"}"
    Backend->>RouterData: from_router_data(router_data)
    RouterData->>RouterData: "raw_path = prepend_frontend_path("/dynamic/42") -> "/prefix/dynamic/42""
    RouterData->>RouterData: "url = ReflexURL(host + "/prefix/dynamic/42")"
    RouterData-->>Backend: "RouterData(url="https://host/prefix/dynamic/42", page.raw_path="/prefix/dynamic/42")"
    Backend-->>Frontend: State delta with updated router
    Frontend-->>Browser: "router.url.path = "/prefix/dynamic/42""

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Comments Outside Diff (1)

1. reflex/istate/data.py, line 450-461 (link)

   get_config() is called twice for every incoming WebSocket message: once inside PageData.from_router_data and again directly in the url= argument. Since the same config value is needed for both, fetching it once and passing it through (or at least caching the result locally) avoids the redundant lookup on every request.

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