Add automated testing to catch breaking changes to StackRunConfig
before they reach users.
- Schema validation: pytest-based test validates old run.yaml files
parse with current StackRunConfig
- Integration tests: run full test suite with old ci-tests run.yaml
to catch runtime semantic issues
- Dual baseline: test against both main (blocks PRs) and latest
release (informational)
- Breaking change acknowledgment: require '!:' in PR title or
'BREAKING CHANGE:' in commit message to merge breaking changes
Resolves#3311
Related to #3237
