[SalesForce] Run specific apex tests during “sfdx force:source:deploy”

After going back through all my commits and using the .forceignore file to exclude certain types of files, I found that the problem was with some static resources. I rebuilt the static resources from the state of the commit, redeployed, and everything worked.

Although I'm not 100% sure, it seems to have been some dependency issue that wasn't showing a helpful error.

You have two choices. First, you can use force:package commands to create an unlocked package. You can install this in production with force:package:install; it is similar to installing an AppExchange package. Otherwise, you would need to use force:source:convert to get a mdapi style format, then use force:mdapi:deploy with the relevant test level (e.g. RunLocalTests) and set rollbackOnError to true. Check out the Salesforce CLI Reference for specific details, or sfdx help force:<command> for command-level help direct from the console. I do not believe that you're currently allowed to create unlocked packages directly via the GUI, but you can open a terminal by using the Terminal > Create New Terminal option, which will open a sfdx environment by default.