You can start a container with a shell that shares the PID and network namespaces of the container you want to debug.

Reading logs/traces on your log aggregation service and reproducing in a dev system?

How do you debug in the dev env without a shell?

from the host system, containers don't exist in a vacuum

remote debugging is a shell

not necessarily. e.g. java runtimes can expose debugging ports when needed that operate on a custom protocol.

or you can just build gdb into the container and run the process under gdb, then attach to the tty.

or you can debug from the host system where the container's pid namespace is a descendant of the root namespace and the other namespaces can be accessed via /proc or unshare.

What I meant is having a remote debugger is as good as having a remote shell in terms of remote code execution.