refactor(sandbox): remove unused pod_template field from CreateSandbox RPC (NVIDIA#522)

Author: drew

architecture/sandbox-custom-containers.md

@@ -67,7 +67,7 @@ The server applies these transforms to every sandbox pod template (`sandbox/mod.
 3. Overrides the agent container's `command` to `/opt/openshell/bin/openshell-sandbox`.
 4. Sets `runAsUser: 0` so the supervisor has root privileges for namespace creation, proxy setup, and Landlock/seccomp.
 
-These transforms apply to both generated templates and user-provided `pod_template` overrides.
+These transforms apply to every generated pod template.
 
 ## CLI Usage
 

crates/openshell-core/src/proto/openshell.datamodel.v1.rs

@@ -92,7 +92,7 @@ const MAX_TEMPLATE_STRING_LEN: usize = 1024;
 /// Maximum number of entries in template map fields (`labels`, `annotations`, `environment`).
 const MAX_TEMPLATE_MAP_ENTRIES: usize = 128;
 
-/// Maximum serialized size (bytes) for template Struct fields (`resources`, `pod_template`,
+/// Maximum serialized size (bytes) for template Struct fields (`resources`,
 /// `volume_claim_templates`).
 const MAX_TEMPLATE_STRUCT_SIZE: usize = 65_536;
 
@@ -3161,14 +3161,6 @@ fn validate_sandbox_template(tmpl: &SandboxTemplate) -> Result<(), Status> {
             )));
         }
     }
-    if let Some(ref s) = tmpl.pod_template {
-        let size = s.encoded_len();
-        if size > MAX_TEMPLATE_STRUCT_SIZE {
-            return Err(Status::invalid_argument(format!(
-                "template.pod_template serialized size exceeds maximum ({size} > {MAX_TEMPLATE_STRUCT_SIZE})"
-            )));
-        }
-    }
     if let Some(ref s) = tmpl.volume_claim_templates {
         let size = s.encoded_len();
         if size > MAX_TEMPLATE_STRUCT_SIZE {