procfs: /proc/sys/fs/aio-max-nr and aio-nr are missing; Redpanda/Seastar aborts at startup

Runtime: runsc release-20261012.0-139-g73eaa38549eb, systrap platform, amd64.

redpanda (Seastar based) aborts at startup:

libc++abi: terminating due to uncaught exception of type std::__1::system_error: open: No such file or directory

/proc/sys/fs/aio-max-nr and /proc/sys/fs/aio-nr do not exist in the sandbox. Seastar reads aio-max-nr at startup with every reactor backend (--reactor-backend=epoll and io_uring abort the same way).

If we mount a writable directory over /proc/sys/fs that contains these two files (1048576 and 0), Redpanda starts, and produce and consume work.

Request

Expose read-only /proc/sys/fs/aio-max-nr and /proc/sys/fs/aio-nr. gVisor already implements io_setup and io_submit.