[evgeny-simplex]

A draft pull request and a manual run (workflow_dispatch) run one build job: ubuntu-24.04 x86-64, GHC 9.6.3, at -O0, with the agent's choice of tests. The full matrix runs when the pull request is marked ready for review and on pushes to master, stable and tags.

• maybe-release outputs reduced (a manual run or a draft). Job build keeps the five-entry matrix and runs when reduced is false; job build-reduced has the one 24.04 x86-64 entry and runs when it is true. Both share env, services and steps through YAML anchors.
• workflow_dispatch with input tests; ready_for_review added to the pull_request types.
• -O0 on pull requests and manual runs, -O2 on pushes.
• Test selection: hspec -m patterns from the tests input, or from a ci-tests block in a draft's description; / runs all tests; with no pattern a reduced run builds without tests; --fail-on=empty when patterns are given. Full runs ignore the selection and run all tests.
• The standard (non-Postgres) build is skipped on reduced runs.
• The Docker image cache is read and written under the repository owner, so forks use their own.
• A manual run on a tag fails in its first step; a release is retried by re-running the jobs of its tag push.

Plan: evgeny-simplex#14

This description has no ci-tests block, so the expected run is build-only: maybe-release, resolver and build-reduced, whose Test step prints "No tests selected"; build is skipped.