Migrate pipeline from CircleCI to GitHub Actions

[phelma]

Part of PP-709.

Cutover to GitHub Actions per the Variant A family plan (gem pilot).
Includes decommission — merging this PR completes the repo's migration.

• main + pr workflows: check/test, prerelease, release environment gate
• PR CI publishes a namespaced pre-release to RubyGems (see below)
• git-crypt unlock on the runner; encrypted CI GPG key moved to .github/
• Slack notifications via rake_slack; dependabot auto-merge job
• Rakefile provisioning swapped to rake_github secrets/environments; rake_circle_ci dropped
• CircleCI pipeline removed: .circleci/, scripts/ci/, the CI SSH deploy
  key pair and its keys:deploy/deploy_keys provisioning, and the stored
  CircleCI/GitHub API credentials (config/secrets/{circle_ci,github}/)

Deliberate decisions (not defects)

This cutover reproduces the CircleCI pipeline's behaviour, warts included;
fixing inherited hazards is post-migration work. In particular:

• ./go release publishes to RubyGems before the version-bump commit is
  pushed — pre-existing ordering inside the untouched release logic.
• Prerelease publishes on every push to main with no approval gate; only
  full releases are gated (environment: release).
• Dependabot auto-merge accepts any update type that passes checks, and the
  merge does not trigger a release build — on CircleCI the merge commit
  carried [skip ci], so this matches. Updates ship with the next
  human-triggered release.
• The release job pulls main at approval time, so a delayed approval
  publishes main as it stands then, not the SHA this run tested — parity with
  the old release.sh (which also pulled; prerelease.sh did not, so the
  prerelease job has no pull).
• asdf_install@v1 is our own action (infrablocks/github-actions); we are
  happy tracking its major version tag.
• Job scaffolding is repeated flat per job by design: the logic lives in the
  build system (./go/rake) and CI stays lean — it just triggers tasks and
  supplies secrets/context.
• Gemfile.lock carries transitive major bumps — the unavoidable resolution
  of the targeted bundle lock --update, not scope creep.
• Small library hunks may appear where the refreshed toolchain's rubocop
  autocorrects existing code (e.g. Style/ArgumentsForwarding) — required
  by the library:check verification gate, not drive-by refactoring.
• Provisioning (pipeline:prepare) authenticates with the operator's ambient
  gh login (GITHUB_TOKEN fallback) instead of a stored PAT — a deliberate
  parity deviation; the stored token in config/secrets/github/config.yaml
  is deleted with the rest of the CircleCI-era credentials.

PR-CI prerelease publish (deliberate, permanent)

pr.yaml has a prerelease job that publishes a namespaced pre-release of
this gem to RubyGems from the PR branch — a permanent CI feature, not
migration-only. This is a deliberate deviation from CircleCI (which published
nothing pre-merge): it proves the publish path before merge instead of
discovering it broken on main. The version is
<committed-version>.pr<PR>.<run>.<attempt> (via the new prerelease:publish
Rakefile task), so it can never collide with main's version:bump[pre]
sequence; the task builds the gem and pushes it straight to RubyGems, then
restores version.rb, so nothing is committed, tagged, or pushed
(gem release is not used — it aborts on the uncommitted version rewrite).
The job is skipped for fork
and Dependabot PRs (they hold no secrets), and merge-pull-request does not
depend on it. PR pre-release versions accumulate permanently on RubyGems —
accepted.

Do not merge manually — the pipeline merges once checks are green.
Disabling the CircleCI project and deleting the CircleCI deploy key are
deferred to the end-of-migration sweep.

---

🏭 This PR was opened by Foundry, Atomic's AI software development
factory. Implementation, review, and fixes are performed by AI agents;
merges happen automatically once the review and checks gates pass.
This task migrates a Ruby gem's CI from CircleCI to GitHub Actions.

Pipeline	Task pack	Family	Run
migrate	migrate-gem	gem	2026-07-22T17-48-59-192Z

_{atomic-foundry-pr · foundry-pipeline: migrate · foundry-task: migrate-gem · foundry-run: 2026-07-22T17-48-59-192Z}

[phelma]

Code Review: #140 - Migrate pipeline from CircleCI to GitHub Actions

Verdict: COMMENT

This CircleCI→GitHub Actions cutover conforms tightly to the Variant A family plan §4. Across correctness, security, safety, standards, and code-quality lenses no critical, major, or minor defects were found: the workflows, Rakefile blocks, gemspec, README, GPG-key move, and CircleCI decommission all match the prescribed shapes, and the release job is correctly parameterised to the repo's deleted release.sh (version:bump[minor], no documentation:update). Only two non-blocking observations remain, one of which is against plan-prescribed code.

Cross-Cutting Themes

• Correct release-job parameterisation (flagged by: correctness, safety, standards) — three lenses independently confirmed the release job mirrors the deleted release.sh (minor bump, git pull, no docs step). No documentation:update task exists in the Rakefile, so the common failure mode of copying the template's docs step verbatim was correctly avoided.

Strengths

• ✅ No workflow injection: all attacker-influenced PR data (title, number, URL, head SHA) is bound via env: and referenced as shell variables, never interpolated into run:. The only ${{ }} in a run: is job.status.
• ✅ Least-privilege tokens: top-level contents: read, elevated per-job only where needed.
• ✅ Correct trust boundary: the secret-bearing PR prerelease job is guarded to same-repo human PRs, and merge-pull-request does not needs: it.
• ✅ --match-head-commit "$HEAD_SHA" preserves merge integrity.
• ✅ Rakefile guards fail fast on a locked clone (missing passphrase / git-crypt ciphertext sentinel) rather than uploading garbage secrets.
• ✅ prerelease:publish wraps the temporary version.rb rewrite in begin/ensure, restoring the file and removing the built gem even on failure.
• ✅ Decommission is complete and clean: no circleci references remain outside docs//Gemfile.lock; only the two portable scripts/ci/common scripts are retained; config/secrets/ci keeps only the git-crypt material.

General Findings

• 🔵 code-quality (plan concern): prerelease:publish uses the replacement-string form source.sub(version_pattern, "\\1#{version}\\3"), which couples correctness to backslash-escape semantics of the interpolated version. Safe today (numeric facts only). This is the plan's verbatim §4.4 step 8 code, so it is a plan concern, not a diff defect.
• 🔵 correctness (false positive): the check/test jobs use ./go test:unit while the deleted test.sh invoked ./go spec. Verified benign — test:unit is the existing RSpec task and the family-canonical name; no spec task exists. Counted nowhere.

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Review generated by /accelerator:review-pr

[phelma]

🔵 Standards (suggestion)

This adds define_repository_tasks to Metrics/BlockLength's AllowedMethods to accommodate the now-larger RakeGithub.define_repository_tasks block (the token-resolution and passphrase-guard logic). The family plan §4 prescribes exact file shapes and includes no .rubocop.yml change; §4.4 only asks that the Rakefile stay clean against the 80-char rule. If this relaxation is genuinely required to pass library:check, it is reasonable — but note it in the PR description as a deliberate deviation so future maintainers can trace it, since it permanently relaxes a lint rule for the repo.