Pure-reference for cross-CI test workflow conventions - when to shard (and how many shards), retry policy (which failures are safe to retry), flake-quarantine integration, artifact retention, per-trigger cadence (per-PR vs per-merge vs nightly), concurrency-cancel patterns, per-job timeouts, secret management, and cross-CI portability. Use as the team's reference for CI test-workflow design across GitHub Actions / GitLab CI / Jenkins / CircleCI; per-CI reporting and per-language reporter / cache-key lookups live in references/, as do the CircleCI test-config patterns (.circleci/config.yml workflows, test splitting, orbs, contexts - references/circleci.md).