### Bug Description The following (valid) form of a platform no longer works: ```yaml platforms: p: - build-on: [amd64] build-for: amd64 ``` It also gives an incredibly unhelpful error message (see below) ### To Reproduce Attempt to run `snapcraft pull --enable-experimental-plugins` on the test at `tests/spread/plugins/craft-parts/kernel`. ### Environment snapcraft 8.13.0 ### snapcraft.yaml ```yaml see above ``` ### Relevant log output ```shell Traceback (most recent call last): File "/snap/snapcraft/x1/lib/python3.12/site-packages/snapcraft/application.py", line 472, in main return app.run() ^^^^^^^^^ File "/snap/snapcraft/x1/lib/python3.12/site-packages/craft_application/application.py", line 663, in run return_code = self._run_inner() ^^^^^^^^^^^^^^^^^ File "/snap/snapcraft/x1/lib/python3.12/site-packages/snapcraft/application.py", line 183, in _run_inner return_code = super()._run_inner() ^^^^^^^^^^^^^^^^^^^^ File "/snap/snapcraft/x1/lib/python3.12/site-packages/craft_application/application.py", line 606, in _run_inner dispatcher = self._get_dispatcher() ^^^^^^^^^^^^^^^^^^^^^^ File "/snap/snapcraft/x1/lib/python3.12/site-packages/snapcraft/application.py", line 410, in _get_dispatcher self._check_for_classic_fallback() File "/snap/snapcraft/x1/lib/python3.12/site-packages/snapcraft/application.py", line 322, in _check_for_classic_fallback raise errors.ClassicFallback() snapcraft.errors.ClassicFallback During handling of the above exception, another exception occurred: Traceback (most recent call last): File "/snap/snapcraft/x1/bin/snapcraft", line 7, in <module> sys.exit(main()) ^^^^^^ File "/snap/snapcraft/x1/lib/python3.12/site-packages/snapcraft/application.py", line 475, in main return cli.run() ^^^^^^^^^ File "/snap/snapcraft/x1/lib/python3.12/site-packages/snapcraft/cli.py", line 259, in run _run_dispatcher(dispatcher, global_args) File "/snap/snapcraft/x1/lib/python3.12/site-packages/snapcraft/cli.py", line 232, in _run_dispatcher dispatcher.run() File "/snap/snapcraft/x1/lib/python3.12/site-packages/craft_cli/dispatcher.py", line 564, in run return self._loaded_command.run(self._parsed_command_args) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/snap/snapcraft/x1/lib/python3.12/site-packages/snapcraft/commands/core22/lifecycle.py", line 268, in run super().run(parsed_args) File "/snap/snapcraft/x1/lib/python3.12/site-packages/snapcraft/commands/core22/lifecycle.py", line 141, in run parts_lifecycle.run(self.name, parsed_args) File "/snap/snapcraft/x1/lib/python3.12/site-packages/snapcraft/parts/lifecycle.py", line 105, in run _run_command( File "/snap/snapcraft/x1/lib/python3.12/site-packages/snapcraft/parts/lifecycle.py", line 141, in _run_command _run_in_provider(project, command_name, parsed_args) File "/snap/snapcraft/x1/lib/python3.12/site-packages/snapcraft/parts/lifecycle.py", line 475, in _run_in_provider cmd.append(project.get_build_for()) ^^^^^^^^^^^^^^^^^^^^^^^ File "/snap/snapcraft/x1/lib/python3.12/site-packages/snapcraft/models/project.py", line 2214, in get_build_for raise RuntimeError("cannot determine build-for architecture") RuntimeError: cannot determine build-for architecture ``` ### Additional context _No response_