docs: promote composable VM images proposal to a design document

The proposal told us to move it under docs/design/ once it was accepted
and implemented.  The systemd base landed on main and the NVIDIA split
(nvidia base + gpu extension) is what this series wires up, so it's no
longer a proposal - promote it to docs/design/composable-vm-images.md,
flip the status accordingly and repoint the in-tree references (agent,
osbuilder and kata-deploy) at the new path.

Signed-off-by: Fabiano Fidêncio <ffidencio@nvidia.com>

docs/design/composable-vm-images.md

@@ -1,9 +1,6 @@
 # Composable VM Images for Kata Containers
 
-> **Status**: Proposal
->
-> Once accepted and implemented, this document should be moved to
-> `docs/design/composable-vm-images.md`.
+> **Status**: Implemented
 
 ## Summary
 

src/agent/kata-extension-mount.sh

@@ -94,7 +94,7 @@ HASH_DEV="${REAL_DEV}${PART_SEP}2"
 #   NO hash device + NO params -> raw mount (genuinely unmeasured extension)
 #
 # See "Integrity policy: measured vs. unmeasured, and failing closed" in
-# docs/design/proposals/composable-vm-images.md for the rationale.
+# docs/design/composable-vm-images.md for the rationale.
 if [[ -b "${HASH_DEV}" ]]; then
 	if [[ -z "${VERITY_PARAMS}" ]]; then
 		echo "ERROR: extension ${EXTENSION_NAME} ships a dm-verity hash device but no verity params were provided on the kernel command line; refusing to mount it unverified" >&2

src/agent/src/guest_extension_image.rs

@@ -21,7 +21,7 @@
 //!
 //! The manifest schema, the `${var}` substitution variables the agent publishes,
 //! and the attester-variant / NVRC contract are documented in
-//! `docs/design/proposals/composable-vm-images.md`, which is the source of
+//! `docs/design/composable-vm-images.md`, which is the source of
 //! truth; this module must stay consistent with it.
 
 use anyhow::{anyhow, bail, Context, Result};

tools/osbuilder/rootfs-builder/nvidia/nvidia_rootfs.sh

@@ -546,7 +546,7 @@ partition_gpu_extension() {
 # This is subtractive on purpose while the monolith still exists: the base is
 # the monolith minus the GPU allow-list. The planned next step inverts this into
 # a purely additive base/extension assembly (monolith = base + extension); see
-# "Additive image assembly" in docs/design/proposals/composable-vm-images.md.
+# "Additive image assembly" in docs/design/composable-vm-images.md.
 partition_base() {
 	echo "nvidia: building driver-agnostic base layout"
 

tools/packaging/kata-deploy/local-build/kata-deploy-binaries.sh

@@ -918,7 +918,7 @@ install_image_nvidia_gpu_confidential() {
 }
 
 # Install the driver-agnostic nvidia base image: the NVRC-init half of the
-# chiseled NVIDIA tree (see docs/design/proposals/composable-vm-images.md).
+# chiseled NVIDIA tree (see docs/design/composable-vm-images.md).
 # The driver still has to be installed to build the shared stage-one (the GPU
 # files are carved out afterwards), so keep the same NVIDIA_GPU_STACK as the
 # monolith.
@@ -936,7 +936,7 @@ install_image_nvidia() {
 
 # Install the gpu extension image: the driver half of the chiseled NVIDIA tree,
 # laid out for /run/kata-extensions/gpu (see
-# docs/design/proposals/composable-vm-images.md).  It is an erofs+verity image
+# docs/design/composable-vm-images.md).  It is an erofs+verity image
 # (MEASURED_ROOTFS) and is driver-versioned, so multiple driver extensions can
 # coexist against a single nvidia base image.
 install_image_nvidia_gpu_extension() {