locally built images are not used if buildkit namespace or nerdctl namespace is not buildkit

[cielavenir]

Description

namespace needs to be buildkit to use locally built image as FROM.

Steps to reproduce the issue

terminal one:

sudo /usr/bin/buildkitd --containerd-worker=true --oci-worker=false --containerd-worker-namespace=default

terminal two:

sudo `which nerdctl` --namespace=default pull alpine:latest
sudo `which nerdctl` --namespace=default build -t alpine:nonexisting1 test1
sudo `which nerdctl` --namespace=default build -t alpine:nonexisting2 test2

Describe the results you received and expected

image should build.

What version of nerdctl are you using?

$ sudo `which nerdctl` version
Client:
 Version:	v1.6.0
 OS/Arch:	linux/amd64
 Git commit:	5f39d76139344b8aac6fd03cbe0fa2fd50f89929
 buildctl:
  Version:	v0.12.2
  GitCommit:	567a99433ca23402d5e9b9f9124005d2e59b8861

Server:
 containerd:
  Version:	1.6.24
  GitCommit:	61f9fd88f79f081d64d6fa3bb1a0dc71ec870523
 runc:
  Version:	1.1.9
  GitCommit:	v1.1.9-0-gccaecfc

$ buildctl --version
buildctl github.com/moby/buildkit v0.12.2 567a99433ca23402d5e9b9f9124005d2e59b8861

$ buildkitd --version
buildkitd github.com/moby/buildkit v0.12.2 567a99433ca23402d5e9b9f9124005d2e59b8861

Are you using a variant of nerdctl? (e.g., Rancher Desktop)

None

Host information

$ sudo which nerdctl info
Client:
Namespace: default
Debug Mode: false

Server:
Server Version: 1.6.24
Storage Driver: overlayfs
Logging Driver: json-file
Cgroup Driver: cgroupfs
Cgroup Version: 1
Plugins:
Log: fluentd journald json-file syslog
Storage: native overlayfs
Security Options:
apparmor
seccomp
Profile: builtin
Kernel Version: 6.1.0-0.deb11.11-amd64
Operating System: Debian GNU/Linux 11 (bullseye)
OSType: linux
Architecture: x86_64
CPUs: 12
Total Memory: 31.28GiB
Name: _______
ID: b0c947b1-ebe4-4934-9ac2-4f8aad5fd613

[cielavenir]

to proper reproduce, I prepared https://github.com/cielavenir/buildkit_issue2550 .

buildkit namespace=default, nerdctl namespace=default
error: failed to solve: lease "8h6nvhvcnge5wwf9ntpxtvhor": not found

buildkit namespace=buildkit, nerdctl namespace=default
error: failed to solve: alpine:nonexisting1: docker.io/library/alpine:nonexisting1: not found

buildkit namespace=buildkit, nerdctl namespace=buildkit
(it works)

setting both builtkit namespace and nerdctl namespace to default causes "lease not found". #1443 says it should be ok but it does not work.

Also, by searching "lease not found", I found rancher-sandbox/rancher-desktop#2584 and saw that setting both buildkit namespace and nerdctl namespace to buildkit works.