feat(podman): honor OCI image working directories

Podman sandboxes now use a custom OCI image WORKDIR as the workspace and
as the working directory for agent commands, matching Docker. Empty, /,
and /sandbox values keep the managed /sandbox workspace volume.

A custom workspace stays in the image's container filesystem: no
workspace volume, no archive upload, and no root setup step. Resolve the
image ID, user, environment, and working directory from one pinned
inspection, validate the workdir with the shared OCI rules, and reject
Podman control-path overlaps and image volumes or driver mounts that
cover it. The runtime starts from / and passes the resolved path to agent
commands with --workdir.

Add podman_oci_identity to the Podman CI test list.

Signed-off-by: Matthew Grossman <mgrossman@nvidia.com>

Author: matthewgrossman

crates/openshell-driver-podman/README.md

@@ -44,7 +44,8 @@ only the channel bootstrap into the existing channel volume, preserving the
 workspace. The workload starts before the supervisor so its user namespace exists
 when the supervisor joins it; a stopped supervisor resolves that namespace again
 on its next start. The driver creates the managed workspace volume owned by
-the workload's final UID and GID, so the workload never starts as root.
+the workload's final UID and GID, so the workload never starts as root. Custom
+image workspaces have no workspace volume or upload.
 
 The runtime must pass the sandbox's unprivileged enforcement probe, including
 nested seccomp notification and Landlock. Unsupported runtime defaults fail
@@ -91,6 +92,20 @@ binary extraction path. `supervisor_image` supplies the dynamically linked
 glibc `/openshell-supervisor` binary outside the workload. Image and request
 environment belong to agent children, never the supervisor process.
 
+## OCI working directory
+
+OpenShell reads `WORKDIR` from the workload image. If it is unset, `/`, or
+`/sandbox`, OpenShell uses its managed `/sandbox` workspace volume. A custom
+path must be absolute and normalized, and cannot overlap `/proc`, `/sys`,
+`/dev`, OpenShell-reserved paths, or the workload's private control and CA
+mounts. Image volumes and driver mounts cannot cover it; mounts nested below it
+remain valid.
+
+A custom path stays in the image's container filesystem with its ownership and
+permissions. The workload starts as the final non-root user, which must be able
+to reach and write the directory. Agent commands use the path as their working
+directory.
+
 ## Lifecycle and readiness
 
 Create builds both stopped containers and stages the private archives before

crates/openshell-driver-podman/src/client.rs

@@ -191,6 +191,10 @@ pub struct ImageConfig {
     pub user: String,
     #[serde(default)]
     pub env: Vec<String>,
+    #[serde(default)]
+    pub working_dir: String,
+    #[serde(default)]
+    pub volumes: Option<HashMap<String, Value>>,
 }
 
 /// Whether a driver-owned volume has exactly the options `OpenShell` creates it
@@ -1226,12 +1230,12 @@ mod tests {
     }
 
     #[tokio::test]
-    async fn inspect_image_reads_immutable_id_and_oci_user() {
+    async fn inspect_image_reads_immutable_id_and_oci_config() {
         let (socket_path, request_log, handle) = spawn_podman_stub(
             "inspect-image",
             vec![StubResponse::new(
                 StatusCode::OK,
-                r#"{"Id":"sha256:immutable","Config":{"User":"app:staff"}}"#,
+                r#"{"Id":"sha256:immutable","Config":{"User":"app:staff","Env":["A=one"],"WorkingDir":"/workspace/project","Volumes":{"/workspace/project/cache":{}}}}"#,
             )],
         );
         let client = PodmanClient::new(socket_path.clone());
@@ -1246,6 +1250,20 @@ mod tests {
             image.config.as_ref().map(|config| config.user.as_str()),
             Some("app:staff")
         );
+        assert_eq!(
+            image
+                .config
+                .as_ref()
+                .map(|config| config.working_dir.as_str()),
+            Some("/workspace/project")
+        );
+        assert!(
+            image
+                .config
+                .as_ref()
+                .and_then(|config| config.volumes.as_ref())
+                .is_some_and(|volumes| volumes.contains_key("/workspace/project/cache"))
+        );
         handle.await.expect("stub task should finish");
         assert_eq!(
             request_log