containerd-worker inside container

I'm trying to run buildkitd with a containerd worker inside a container, but if fails without a clear error message.
My container:

# syntax = docker/dockerfile:1.7
FROM debian:unstable

RUN apt-get update && apt-get install -y \
    git containerd supervisor \
    && rm -rf /var/lib/apt/lists/*

COPY --link etc /etc
COPY --link --from=moby/buildkit:latest /usr/bin/buildkitd /usr/bin/buildkitd
COPY --link --from=moby/buildkit:latest /usr/bin/buildctl /usr/bin/buildctl

ENTRYPOINT ["/usr/bin/supervisord"]

my /etc/supervisord.conf:

; this is a comment
[supervisord]
nodaemon=true
logfile=/dev/stdout
logfile_maxbytes=0
logfile_backups=0
loglevel=warn
user=root

[program:containerd]
command=containerd

stdout_logfile=/dev/stdout
stdout_logfile_maxbytes=0
stderr_logfile=/dev/stderr
stderr_logfile_maxbytes=0

[program:buildkitd]
; this works fine
; command=buildkitd --addr=tcp://0.0.0.0:1234 --addr=unix:///run/buildkit/buildkitd.sock

; this fails
command=buildkitd --debug --oci-worker=false --containerd-worker=true --addr=tcp://0.0.0.0:1234 --addr=unix:///run/buildkit/buildkitd.sock

stdout_logfile=/dev/stdout
stdout_logfile_maxbytes=0
stderr_logfile=/dev/stderr
stderr_logfile_maxbytes=0

exec'ing into this container that's running with --privileged and running:

cat <<EOF > Dockerfile
FROM alpine
RUN echo hello
EOF

buildctl build \
  --progress=plain --frontend=dockerfile.v0 --local context=. --local dockerfile=. \
  --output type=image,name=test,push=false

errors with:

....
#4 [1/2] FROM docker.io/library/alpine:latest@sha256:c5b1261d6d3e43071626931fc004f70149baeba2c8ec672bd4f27761f8e1ad6b
#4 resolve docker.io/library/alpine:latest@sha256:c5b1261d6d3e43071626931fc004f70149baeba2c8ec672bd4f27761f8e1ad6b 0.0s done
#4 sha256:bca4290a96390d7a6fc6f2f9929370d06f8dfcacba591c76e3d5c5044e7f420c 0B / 3.35MB 0.2s
#4 sha256:bca4290a96390d7a6fc6f2f9929370d06f8dfcacba591c76e3d5c5044e7f420c 3.35MB / 3.35MB 0.3s done
#4 extracting sha256:bca4290a96390d7a6fc6f2f9929370d06f8dfcacba591c76e3d5c5044e7f420c 0.1s done
#4 DONE 0.4s

#5 [2/2] RUN echo hello
#5 ERROR: process "/bin/sh -c echo hello" did not complete successfully: invalid argument
------
 > [2/2] RUN echo hello:
------
Dockerfile:2
--------------------
   1 |     FROM alpine
   2 | >>> RUN echo hello
   3 |     
--------------------
error: failed to solve: process "/bin/sh -c echo hello" did not complete successfully: invalid argument

Should this work? Am I'm doing something wrong?

Reproduce the setup from the container Dockerfile and /etc/supervisord.conf, using the shown buildctl command and privileged container. Compare the buildkitd and containerd output for the containerd-worker configuration; done means determining whether this setup is supported and providing a clear cause or actionable error for the invalid argument failure.