fix(cdi): preserve GPU sandbox compatibility

Signed-off-by: Evan Lezar <elezar@nvidia.com>

Author: elezar

crates/openshell-driver-docker/README.md

@@ -134,18 +134,29 @@ inventory, then passes the same IDs to Docker with a CDI `DeviceRequest`.
 For a GPU sandbox, the driver writes those IDs and projected CDI spec directory
 paths to a versioned context in the protected workload boundary configuration.
 It uses structured, read-only, non-recursive binds at `/.openshell/cdi-specs/<index>`.
-Docker validates source existence on the daemon host; missing directories fail
-container creation without being created. OpenShell does not relabel the host
-spec directories. Administrators must make the existing directories readable
+The driver checks source existence on the daemon host using one temporary,
+stopped container per directory and the prepared workload image. Each probe has
+one read-only, private bind with source creation disabled. Successful probes are
+removed with anonymous image-volume cleanup, including after provisioning
+cancellation. Confirmed missing directories are omitted; other errors fail
+provisioning. Results are cached for 30 seconds and refreshed on demand; observed
+changes to daemon identity, configured directories, or GPU inventory invalidate
+the cache. The resulting context records only available projections. The actual
+sandbox is created once, and selected devices must still resolve from the
+projected specs. No probe starts a process, creates missing directories, or
+relabels host spec directories. Administrators must make the existing directories readable
 under the host's SELinux policy when SELinux is enabled.
 
 Whole spec directories are available to the trusted runtime, which resolves only
 the selected devices. The mandatory Landlock baseline hides these projections
 from agent processes, even when the authored policy grants a broad ancestor.
 The sandbox runtime resolves the selected devices in that mount namespace before
 it launches agent processes and derives Landlock paths and supplemental groups
-from CDI `containerEdits`. A missing context or spec directory fails workload
-startup closed. Non-GPU sandboxes receive no CDI context or spec mounts.
+from CDI `containerEdits`. Containers with CDI context fail startup if their
+selected devices cannot be resolved. Existing GPU containers without context
+retain legacy baseline handling on restart. Admission checks persisted context
+for existing containers and the creation context for new ones. Non-GPU sandboxes
+receive no CDI context or spec mounts.
 
 ## Driver Config Mounts