### Bug Description When trying to declare an abstract socket in a `snapcraft.yaml` file it caused validation to fail, even though it's supported by `snapd` [[1]](https://snapcraft.io/docs/snapcraft-app-and-service-metadata) [[2]](https://forum.snapcraft.io/t/socket-activation-support/2050/7). I was able to trace this back to an incomplete regex used for validation that doesn't support the possibility of sockets in abstract namespaces [here](https://github.com/snapcore/snapcraft/blob/dbe76f21d0e670811a05f6fa7838e704bbfaa52d/snapcraft/projects.py#L175-L195). ### To Reproduce Try to build the `snapcraft.yaml` file with `snapcraft -v`. ### Environment Ubuntu 23.04, snapcraft 7.4.3 ### snapcraft.yaml ```shell name: lldpad base: core22 confinement: devmode description: 'Redacted' summary: Link Layer Discovery Protocol Implementation (Runtime) version: 1.1+git20221028.aa18720-1-snap parts: lldpad: plugin: nil stage-packages: - lldpad apps: lldpad: command: /usr/sbin/lldpad daemon: simple plugs: - network-bind - browser-support sockets: unix: listen-stream: "@snap.lldpad./com/intel/lldpad" ``` ### Relevant log output ```shell Starting Snapcraft 7.4.3 Logging execution to '/home/phckopper/.local/state/snapcraft/log/snapcraft-20230719-203033.689783.log' Running on amd64 for amd64 Bad snapcraft.yaml content: - '@snap.lldpad./com/intel/lldpad' is not a valid socket path (e.g. /tmp/mysocket.sock). (in field 'apps.lldpad.sockets.unix.listen-stream') Full execution log: '/home/phckopper/.local/state/snapcraft/log/snapcraft-20230719-203033.689783.log ``` ### Additional context [How snapd validates internally](https://github.com/snapcore/snapd/blob/876953a4a80ee319aa4e175eaf81b0eefec6748c/snap/validate.go#L202)