vxn: add containerd OCI runtime integration

Add shell-based OCI runtime (vxn-oci-runtime) that enables containerd
to manage Xen DomU containers through the standard runc shim. Non-terminal
container output flows back to ctr via the shim's pipe mechanism.

New files:
- vxn-oci-runtime: OCI runtime (create/start/state/kill/delete/features/logs)
- vxn-sendtty.c: SCM_RIGHTS helper for terminal mode PTY passing
- containerd-shim-vxn-v2: PATH trick wrapper for runc shim coexistence
- containerd-config-vxn.toml: CRI config (vxn default, runc fallback)
- vctr: convenience wrapper injecting --runtime io.containerd.vxn.v2

Key design:
- Monitor subprocess uses wait on xl console (not sleep-polling) for
  instant reaction when domain dies, then extracts output markers and
  writes to stdout (shim pipe -> containerd FIFO -> ctr client)
- cmd_state checks monitor PID liveness (not domain status) to prevent
  premature cleanup race that killed monitor before output
- cmd_delete always destroys remnant domains (no --force needed)
- Coexists with runc: /usr/libexec/vxn/shim/runc symlink + PATH trick

Verified: vctr run --rm, vctr run -d, vxn standalone, vxn daemon mode.

Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>

0 files changed, 0 insertions, 0 deletions