## Summary
- allow `socketpair(AF_UNIX, ...)` in the proxy-routed Linux seccomp
mode
- continue denying `socket(AF_UNIX, ...)` so user commands cannot create
pathname or abstract Unix sockets
- extend the managed-proxy integration test to verify both behaviors
## Root cause
`NetworkSeccompMode::ProxyRouted` treated anonymous Unix socket pairs
like externally addressable Unix sockets and returned `EPERM`. This
breaks tools that use socket pairs for local child-process IPC even
though a socket pair cannot connect outside the sandbox or bypass the
routed proxy.
`dangerously_allow_all_unix_sockets` controls Unix-socket requests
forwarded by the managed network proxy; it does not currently configure
the Linux seccomp filter. Socket pairs should not require that dangerous
setting because they are unnamed, process-local IPC.
Related but independent: #26553 fixes host proxy bridge socket path
length handling.
---------
Co-authored-by: Codex <noreply@openai.com>
d40454522e