Feature summary (what you would like to be able to do and where):
When using a deploy token (https://wikitech.wikimedia.org/wiki/Help:Toolforge/Deploy_your_tool#Triggering_a_deployment_from_your_CI_runner) it would be very useful to allow the ref to be provided as a URL parameter, overriding the ref specified on the component config.
Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):
I have a number of tools which are deployed from git tags, which are created from the main (default) branch by a human. This is preferable to deploying directly from main as it allows testing both multiple merged changes and pushing the tool to a staging user outside of the production user.
--ref is allowed in the build start command today and I use it (from a fabric based script) to handle building/restarting aka deploying.
Benefits (why should this be implemented?):
This would generally ease the deployment of tools (e.g. not having to maintain a production branch), additionally providing a means to roll forwards/back or deploy test releases.
For my tools it would remove a significant dependency on the bastion hosts.