New memcached status code leads to an unrelated CAS error being printed by pillowfight

When running a Couchbase Server that has 'scope data limits' enabled, libcouchbase shows a confusing/unexpected message when the data-limit his reached, in this case memcached fails mutation commands with status 0x34 and the following is displayed by pillowfight Operation(s) failed: LCB_ERR_CAS_MISMATCH (209): CAS mismatch.

Some brief discussion suggest this is just because the libcouchbase I used didn't support the V2 error map, so please close this issue if another ticket tracks that work
and this ticket is expected behaviour for the down-level libcouchbase (although an improvement/suggestion would be to not print CAS_MISMATCH, this is confusing, a raw status may of been more useful for people to debug issues).

To reproduce I think the following works without a source build.

• Install this toy-build
  • http://latestbuilds.service.couchbase.com/builds/latestbuilds/couchbase-server/toybuilds/13784/couchbase-server-enterprise-7.1.0-13784-centos7.x86_64.rpm
• Create a single node cluster and add one bucket (default in this example)
• Create a scope with a small data limit (0 might work, but this is what I used at the time of testing)

  curl -s cluster-ip:8091/pools/default/buckets/default/scopes -u Administrator:asdasd -d name=s1 -d 'limits={"kv":{"data_size": 100000}}'

• Add a collection to the new scope

  couchbase-cli collection-manage -c cluster-ip:8091 -u Administrator -p asdasd --bucket default --create-collection s1.jim

Now run pillowfight so it hits the data limit

cbc-pillowfight -U 'couchbase://cluster-ip:11210/default' -u Administrator -P asdasd -m 500 -M 500 -I 1000000 --populate-only --collection s1.jim

Note in my testing I was using libcouchbase from my server build with the following SHA

• 494582fa 2021-10-13 | CCBC-1510: fix key length calculation for exists/get/touch/unlock (HEAD, m/master) [Sergey Avseyev]

cbc-pillowfight will eventually return:

Operation(s) failed: LCB_ERR_CAS_MISMATCH (209): CAS mismatch

If the toy-build is not required/wanted a server build can be used from this SHA that represent the feature in development

• https://github.com/jimwwalker/kv_engine/commit/08063c8b534bfaf94f428c4ec9073626a97d73fa

Also fyi the new status code was added here http://review.couchbase.org/c/kv_engine/+/164048