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>

1 files changed, 16 insertions, 0 deletions

diff --git a/recipes-containers/vcontainer/files/vctr b/recipes-containers/vcontainer/files/vctr
new file mode 100644
index 00000000..ca84644a
--- /dev/null
+++ b/recipes-containers/vcontainer/files/vctr
@@ -0,0 +1,16 @@
+#!/bin/sh
+# vctr - convenience wrapper for ctr with vxn runtime
+# Usage: vctr run <image> <cmd>   (same as: ctr run --runtime io.containerd.vxn.v2 ...)
+#        vctr <any ctr command>   (passed through to ctr)
+
+VXN_RUNTIME="io.containerd.vxn.v2"
+
+case "$1" in
+    run)
+        shift
+        exec ctr run --runtime "$VXN_RUNTIME" "$@"
+        ;;
+    *)
+        exec ctr "$@"
+        ;;
+esac