Problem

There is no automated release process. Versioning is hard-coded in mix.exs ("0.1.0"), there is no CI step to create releases, and publishing to Hex requires manual intervention. The huorn-minecraft project has a working model: CalVer version computation, automatic changelog from git log, artifact attachment, and tag creation — all driven by Anvil CI.

Desired Workflow

On every push to main, after all checks pass (compile, format, dialyzer, test):

1. Compute version — CalVer YYYY.MM.BUILD (e.g., 2026.04.1), incrementing build within a month, resetting on new month. Query anvil release list for the latest tag.
2. Build — mix compile --warnings-as-errors (already exists)
3. Test — mix test (already exists)
4. Generate changelog — git log --oneline <last-tag>..HEAD
5. Create Hex package — mix hex.build to produce the .tar artifact
6. Create Anvil release — anvil release create --tag <VERSION> --title "ExGitObjectstore <VERSION>" --body "<CHANGELOG>" --attach <hex-tar>
7. Tag commit — git tag <VERSION> && git push origin <VERSION>

Acceptance Criteria

• ci/release.sh script computes CalVer version from anvil release list
• .anvil.yml has a release step that runs after all checks pass, only on main
• mix.exs version is dynamically set from $VERSION env var at build time, falling back to "0.0.0-dev" for local builds
• Changelog is auto-generated from git log between previous tag and HEAD
• Anvil release is created with the version tag, changelog body, and hex package attached
• Git tag is created and pushed for each release
• ExDoc is generated and attached to the release as a tarball
• Release step is idempotent — re-running on same commit doesn’t create duplicates
• Local mix compile and mix test still work without $VERSION set (dev default)

Notes

• Modeled after huorn-minecraft’s ci/release.sh + .anvil-ci.yml pattern
• CalVer chosen over SemVer because this library is under active development with frequent releases — CalVer avoids bikeshedding on major/minor/patch
• Hex publishing can be deferred (requires API key setup) — initial version should create the Anvil release + tag only