Bug

locale_selector() in vibetuner/frontend/middleware.py re-parses the request path to detect a language prefix:

def locale_selector(conn: HTTPConnection) -> str | None:
    parts = conn.scope.get("path", "").strip("/").split("/")
    if parts and len(parts[0]) == 2 and parts[0].islower() and parts[0].isalpha():
        return parts[0]
    return None

But LangPrefixMiddleware has already stripped the prefix from scope["path"] and stored it in scope["state"]["lang_prefix"]. So by the time locale_selector runs inside LocaleMiddleware, the path is / and it returns None.

Expected

Visiting /ca/ should detect Catalan as the locale, persist it via AdjustLangCookieMiddleware, and make it sticky.

Actual

The language prefix is ignored for locale detection. The cookie never gets updated, so the language doesn't persist.

Suggested Fix

locale_selector should read from scope["state"]["lang_prefix"]:

def locale_selector(conn: HTTPConnection) -> str | None:
    return conn.scope.get("state", {}).get("lang_prefix")

Filed by Claude Code.