NetSurf: what GTK's images and libcurl's resolver needed

NetSurf (GTK 3) now starts under X and loads pages over HTTPS. Every icon
GTK draws goes gdk-pixbuf -> glycin -> a loader process -> a sealed memfd
-> GMappedFile, and each hop found something missing:

- mkaroot runs Alpine's package triggers in the root under bubblewrap.
  --no-scripts had skipped them, so there was no MIME cache, pixbuf loader
  list, compiled GSettings schemas, GIO module cache, font cache or busybox
  applet links.
- /usr/bin/bwrap is a stand-in that parses bubblewrap's options and runs
  the program with no sandbox: glycin starts its loaders only through bwrap,
  and real bwrap needs namespaces. schos-base replaces bubblewrap for it.
- ioctl: FIOCLEX, FIONCLEX, FIONBIO and FIOASYNC on any descriptor (Rust's
  std uses them; pipes and sockets answered ENOTTY).
- capget/capset: root has every capability, others none.
- socketpair accepts SOCK_DGRAM and SOCK_SEQPACKET, carried as a stream.
- waitpid and setpgid match children against the thread group leader, so a
  thread can wait for the process it spawned (ECHILD before).
- memfd: fstat reports the ftruncate length, not the page-rounded one; file
  seals (F_ADD_SEALS, F_GET_SEALS, MFD_ALLOW_SEALING) are recorded and
  enforced on later writes, truncation and writable mappings; MFD_CLOEXEC
  is honoured; read-only MAP_PRIVATE maps are allowed.
- recvfrom honours O_NONBLOCK and MSG_DONTWAIT. musl's resolver reads its
  socket until EAGAIN and blocked for ever after the first DNS answer.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4

kernel/sys/table.inc

@@ -298,6 +298,8 @@ SYSCALL(205,        284, eventfd)
 SYSCALL(206,         73, flock)
 SYSCALL(207,         51, getsockname)
 SYSCALL(208,         52, getpeername)
+SYSCALL(209,        125, capget)
+SYSCALL(210,        126, capset)
 
 // --- mounts ---
 SYSCALL(185,        165, mount)