Yeah, warnings are lexically scoped, so turning them off in one place only suppresses them if that's where they are generated.

In this case you need to get a bit more invasive: catch all warnings for the duration of the call, and rethrow all but the one you want to avoid:

{
  local $SIG{__WARN__} = sub {
    warn @_ unless $_[0] =~ /^Deep recursion/;
  };
  $ent->delete;
}
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Note that it is safe to warn inside the warnings handler - the handler is suppressed while it is being called.