- [ x] Have you followed the guidelines for contributing? - [ x] Have you signed the [CLA](http://www.ubuntu.com/legal/contributors/)? - [x ] Have you successfully run `make lint && make test`? - [ ] Have you added an entry to the changelog (`docs/reference/changelog.rst`)? --- **Summary of Changes** This PR introduces the new override-overlay feature, enabling execution of an overlay scriptlet inside a chrooted environment as an alternative to the existing overlay-script mechanism. **Key Updates** Grammar: Added override-overlay keyword. Validation: Added schema validation ensuring override-overlay is mutually exclusive with overlay-script. **Execution logic:** When override-overlay is set, run the scriptlet from within a minimal chroot. Added necessary mountpoints (/usr, /bin, /lib64, /lib) to support chroot execution. Hashing: Included override-overlay in layer hashing to ensure proper rebuild triggers. Tests: Updated marshalling/unmarshalling tests to include the new field when not setted. **Impact** This feature expands overlay customization capabilities while preserving backwards compatibility. Standard overlay-script continues to function normally when override-overlay is not provided. **Testing** I tested the feature using the following parts.yaml, which exercises the override-overlay scriptlet inside the chroot and verifies environment behavior through proof.txt, using : python -m craft_parts --overlay-base <basedir> [clean] ``` parts: hello: plugin: nil source: hello.sh source-type: file #overlay-script: | override-overlay: | echo "==== CHROOT TEST ===" > proof.txt echo "PWD: $(pwd)" >> proof.txt echo "result of : ls -l ." >> proof.txt ls -l . >> proof.txt readlink -f / >> proof.txt override-build: | cp hello.sh "${CRAFT_PART_INSTALL}/hello" chmod +x "${CRAFT_PART_INSTALL}/hello" stage: - "*" prime: - "*" ```