### Bug Description When building a core20 project _not_ using the architecture shorthand, `--build-for` produces the following error: ``` Error: Cannot use --build-on, architecture list is already set in snapcraft.yaml. ``` ### To Reproduce Run `snapcraft remote-build --build-for amd64` with the attached project. ### Environment snapcraft 8.12.0, ubuntu 25.04 ### snapcraft.yaml ```yaml name: testing # you probably want to 'snapcraft register <name>' base: core20 # the base snap is the execution environment for this snap version: "0.1" # just for humans, typically '1.2+git' or '1.3.2' summary: Single-line elevator pitch for your amazing snap # 79 char long summary description: | This is my-snap's description. You have a paragraph or two to tell the most important story about your snap. Keep it under 100 words though, we live in tweetspace and your description wants to look good in the snap store. grade: devel # must be 'stable' to release into candidate/stable channels confinement: devmode # use 'strict' once you have the right plugs and slots architectures: - build-on: [arm64] run-on: [arm64] - build-on: [amd64] run-on: [amd64] parts: my-part: # See 'snapcraft plugins' plugin: nil ``` ### Relevant log output ```shell n/a ``` ### Additional context _No response_