Track upstream rcl_buffer::Buffer<T> adoption and phase out custom shadowing types

[sykwer]

Background

An upstream proposal is in progress to modify rosidl_generator_cpp so that uint8[] fields in message definitions are generated as rcl_buffer::Buffer<uint8_t> instead of std::vector<uint8_t>. Concretely, this means types like sensor_msgs::msg::Image or sensor_msgs::msg::PointCloud2::data would carry a rcl_buffer::Buffer<uint8_t> in the upstream ROS 2 type system.

Buffer<T> is designed with a polymorphic backend, allowing it to hold pointers to data residing on either CPU or GPU memory under a single unified type.

Impact on Agnocast

This change is a strong tailwind for Agnocast's GPU memory support:

• Custom shadowing types become unnecessary.
  Currently, handling GPU-backed PointCloud2 or Image data requires maintaining custom wrapper classes that shadow the upstream message types (e.g., duplicating the data field with a GPU-aware allocator). Once rcl_buffer::Buffer<T> lands upstream, the vanilla message types can be used as-is.

• GPU memory lifetime management remains Agnocast's responsibility.
  This upstream change is not the same as Agnocast's GPU memory support. The lifetime of GPU memory across processes — tracked via ipc_shared_ptr — is still uniquely Agnocast's concern and remains a core differentiator of our zero-copy IPC design.

Action Items

• Monitor the upstream rosidl_generator_cpp proposal and track its progress toward merge
• Track Fast DDS backend support, as the current prototype targets rmw_zenoh_cpp only
• Maintain existing custom shadowing types during the transition period until the upstream change stabilizes and is released
• Plan migration: replace shadowing types with native upstream message types once rcl_buffer::Buffer<T> is available
• Evaluate whether ipc_shared_ptr lifetime semantics need any adjustment when wrapping Buffer<T>-backed messages

References

• Working prototype of native buffers / accelerated memory transport (ROS Discourse, Feb 2026)
• Update on ROS native buffers (ROS Discourse, preceding post)
• Accelerated Memory Transport Working Group
• nvcyc/ros2 meta repo (prototype source)