### Bug Description ## Summary The python plugin fails to build snaps targeting `core26` because the base snap no longer includes a Python interpreter. The plugin assumes Python will be available either in the staged payload or in the base, but core26 has removed Python from the base. ## Steps to Reproduce 1. Create a snap using the python plugin with `base: core26` 2. Run `snapcraft` ## Expected Behavior Either: - The python plugin automatically stages Python when the base doesn't include it, OR - The plugin fails early with a clear error message instructing the user to add `python3-venv` to `stage-packages` ## Actual Behavior The build fails late in the process with: Looking for a Python interpreter called "python3.14" in the payload... Python interpreter not found in payload. No suitable Python interpreter found, giving up. ## Details The `BasePythonPlugin` in `craft_parts/plugins/base.py`: 1. Declares `python3-dev` and `python3-venv` as **build-packages** 2. Creates a venv using the build environment's Python 3. Searches for Python in the payload (install_dir/stage_dir) 4. Falls back to `$(readlink -f "$(which python3)")` assuming it exists at runtime This fallback worked when bases (core22, core24) included Python, but breaks on core26 where Python was removed. $ ls /snap/core24/current/usr/bin/python* /snap/core24/current/usr/bin/python3 -> python3.12 /snap/core24/current/usr/bin/python3.12 $ ls /snap/core26/current/usr/bin/python* zsh: no matches found: /snap/core26/current/usr/bin/python* ## Ideas for a fix **Auto-stage Python when needed** - Detect when the target base lacks Python and automatically add `python3-venv` to stage-packages **Fail early with guidance** - Check for Python in the base during validation and emit a clear error: ``` Error: base 'core26' does not include Python. Add 'python3-venv' to stage-packages. ``` ## Workaround Manually add `python3-venv` to `stage-packages` in `snapcraft.yaml`. ## Environment - snapcraft 9.0.1 - craft-parts (bundled with snapcraft) - base: core26 (Ubuntu 26.04 / Resolute) ### part yaml ```shell parts: test: plugin: python source: . build-packages: - git stage-packages: - git - openssh-client python-packages: - ./[...] override-pull: | craftctl default craftctl set version="$(git describe --tags --always)" ``` ### Relevant log output ```shell :: 2026-08-10 18:24:49.949 :: + python3 -m venv /root/parts/[...]/install :: 2026-08-10 18:24:49.949 :: Error: [Errno 13] Permission denied: '/root/parts/[...]/install/bin/python3' :: 2026-08-10 18:24:49.949 Check the build output and verify the project can work with the 'python' plugin. ```