The websockets dials got proxy=None but the three HTTP /json/version dials
(CDP override discovery, is_browser_debug_ready used by Lightpanda and the
real-profile readiness check, and surviving-Chrome detection) still resolved
via getproxies(), so under a system/env proxy discovery fell back to the raw
http:// URL, readiness never fired and /browser connect reported not ready.
loopback_request_kwargs() sits next to loopback_connect_kwargs() and is used
at all three sites (ProxyHandler({}) opener for the urllib one).
add_loopback_no_proxy turned an operator NO_PROXY=* into '*,127.0.0.1,...',
which urllib/requests no longer treat as the wildcard, flipping bypass-all
configs into proxy-all. A wildcard in either casing now leaves env untouched.
is_loopback_host also accepts any loopback IP literal (127.x, ::ffff:127.0.0.1).
Review finding: HTTP /json/version dials still proxied loopback; NO_PROXY=* wildcard broken by append.
Move the loopback NO_PROXY merge from browser_tool into agent/proxy_bypass.py (the
module that already owns NO_PROXY semantics) and reuse no_proxy_entries() so comma-
and whitespace-separated operator values are both preserved. Add
loopback_connect_kwargs() and pass proxy=None on the two in-process websockets
dials to loopback CDP endpoints (browser_cdp_tool._cdp_call, BrowserSupervisor._run):
those never see the child env, so the env merge alone left them routed through a
macOS system proxy. Remote CDP URLs keep the default proxy behaviour.
Tests trimmed to two invariants: the built child env appends loopback to an
operator NO_PROXY in both casings, and only loopback URLs get proxy=None.
Sibling helper in tools/browser_use_cli (#110570) is redundant once the shared
env carries the entries.
websockets>=14 defaults to proxy=True and resolves proxies via
urllib.request.getproxies(), which reads the macOS/Windows system
proxy config even with no *_proxy env vars set. Local CDP endpoints
(ws://127.0.0.1:<port>/devtools/...) were therefore dialed through
the system proxy and the handshake failed with "did not receive a
valid HTTP response" (#110565).
Append 127.0.0.1/localhost/::1 to NO_PROXY/no_proxy (both casings)
in _build_browser_env so every browser subprocess (Browser Use CLI,
agent-browser, Chromium, Lightpanda) bypasses proxies for loopback.
Operator-provided NO_PROXY entries are preserved.
Fixes#110565
teknium1