Fixes 'exit proxy never used in chain' and 'browsers break when chain is green'. Chain Builder gets a Save-as-final-hop button that appends the typed exit proxy to the manual chain. On engage, Chromium browsers get pinned to our proxy via HKLM policy (ProxyMode=fixed_servers, ProxyServer, ProxyBypassList) and QuicAllowed=0 so HTTP/3 doesn't bypass HTTP proxies and stall under the kill-switch. Chain start now runs check_https_tunnel and warns clearly when proxies forward HTTP but refuse CONNECT — the real cause of green-chain-yet-blank-browser.
Co-authored-by: Cursor <cursoragent@cursor.com>
httpx.AsyncClient.get() does not accept proxy= per-request.
Shared client caused every check_one call to raise TypeError,
silently caught as False, so 0/N proxies ever passed.
Reverted to per-proxy AsyncClient(proxy=url) in _check_one.
Semaphore concurrency + wall-clock cap preserved.
Also re-adds _check_one helper that was accidentally removed.
Made-with: Cursor
