[K8s] Fix rsync Not Found (#7844)

* Suppress future warning for launch output.

* fix syntax.

* Remove future warning using grep.

* Sleep if not present.

* Clean up.

* Wait for rsync on remote.

Author: lloyd-brown

sky/utils/kubernetes/rsync_helper.sh

@@ -48,8 +48,14 @@ fi
 
 if [ -z "$context" ] || [ "$context_lower" = "none" ]; then
     # If context is none, it means we are using incluster auth. In this case,
-    # use need to set KUBECONFIG to /dev/null to avoid using kubeconfig file.
-    kubectl exec -i "$resource_type/$resource_name" -n "$namespace" --kubeconfig=/dev/null -- "$@"
+    # we need to set KUBECONFIG to /dev/null to avoid using kubeconfig file.
+    kubectl_cmd_base="kubectl exec \"$resource_type/$resource_name\" -n \"$namespace\" --kubeconfig=/dev/null --"
 else
-    kubectl exec -i "$resource_type/$resource_name" -n "$namespace" --context="$context" -- "$@"
+    kubectl_cmd_base="kubectl exec \"$resource_type/$resource_name\" -n \"$namespace\" --context=\"$context\" --"
 fi
+
+# Execute command on remote pod, waiting for rsync to be available first.
+# The waiting happens on the remote pod, not locally, which is more efficient
+# and reliable than polling from the local machine.
+# We wrap the command in a bash script that waits for rsync, then execs the original command.
+eval "${kubectl_cmd_base% --} -i -- bash -c 'until which rsync >/dev/null 2>&1; do sleep 0.5; done; exec \"\$@\"' -- \"\$@\""