ci: migrate the Homebrew tap from a formula to a cask

[sergiught]

📝 Summary

goreleaser check fails on our config with DEPRECATED: brews should not be used anymore — note the stronger wording than the dockers notice in #115: this one is "should not be used", not "being phased out".

The reason is Homebrew's own taxonomy, not a goreleaser preference. From Acceptable-Casks.md:

Casks distribute applications and other pre-built files published by the upstream developer.
Open-source command-line-only software normally belongs in homebrew/core as a formula built from source.

Our brews block only ever emitted a formula that downloads the prebuilt release tarball and copies the binary out — a cask wearing a formula's clothes. homebrew_casks puts it on the right side of that line.

Secondary win: the hand-written extra_install Ruby is replaced by declarative completions:/manpages: fields, and the man/*.1 glob expands to all 53 generated pages by itself.

🔄 Existing users migrate automatically

This PR also ships packaging/homebrew-tap/tap_migrations.json. Homebrew's update reporter has a dedicated same-tap formula→cask path — Library/Homebrew/cmd/update_report/reporter.rb, in migrate_tap_migration:

if new_tap.core_cask_tap? || new_tap.cask_tokens.intersect?([new_full_name, new_name])
  migration_message = if new_tap == tap
    "#{full_name} has been migrated from a formula to a cask."

When it fires, brew update runs brew unlink ofga, brew cleanup, then brew install --cask sergiught/tap/ofga, and tells the user to brew uninstall --formula --force ofga at their convenience. {"ofga": "ofga"} is the mapping that resolves to the fully-qualified cask token (tracing the name-resolution branches in that same method).

Without this file, existing installs would keep a formula that stops receiving updates, silently. With it, no user action is required and no reinstall instructions are needed.

🚚 Merge steps in the tap repo

This PR cannot complete the migration on its own — sergiught/homebrew-tap needs two manual changes, ideally in the same commit, timed with the first release on this config:

1. Add tap_migrations.json (copy from packaging/homebrew-tap/tap_migrations.json).
2. Delete Formula/ofga.rb. goreleaser writes Casks/ofga.rb but will not remove the old formula. If it stays, the tap carries a stale formula pinned at 0.267.0 alongside the cask.

📥 How users install

Unchanged — brew install accepts formula|cask, so the documented command still resolves:

brew install sergiught/tap/ofga

brew upgrade ofga and brew uninstall ofga also work on casks (brew upgrade is documented over installed_formula | installed_cask). No docs changes needed to README.md:100 or docs/site/src/content/docs/guide/installation.mdx.

Casks support Linux — Homebrew's Cask Cookbook documents on_linux and depends_on :linux — so no platform coverage is lost. The generated cask carries all four macOS/Linux × intel/arm combinations.

🏷 Type of change

• 🐛 Bug fix (non-breaking)
• ✨ Feature (non-breaking)
• 💥 Breaking change (users must update)
• ♻️ Refactor (no functional change)
• 📚 Docs only
• 🛠 Build / CI / tooling

✅ How to verify

goreleaser check   # brews deprecation gone
goreleaser release --snapshot --clean --skip=sbom,nfpm,aur,sign,docker
cat dist/homebrew/Casks/ofga.rb

Generated locally with goreleaser v2.17.0 — abridged:

cask "ofga" do
  on_macos do
    on_intel do  sha256 "f4a92a17…"  url "…/ofga_Darwin_x86_64.tar.gz"  end
    on_arm   do  sha256 "9fac3276…"  url "…/ofga_Darwin_arm64.tar.gz"   end
  end
  on_linux do
    on_intel do  sha256 "4e0140aa…"  url "…/ofga_Linux_x86_64.tar.gz"   end
    on_arm   do  sha256 "b435c0a8…"  url "…/ofga_Linux_arm64.tar.gz"    end
  end
  binary "ofga"
  manpage "man/ofga-api.1"   # …53 manpage lines, expanded from the glob…
  bash_completion "completions/ofga.bash"
  fish_completion "completions/ofga.fish"
  zsh_completion  "completions/ofga.zsh"
  postflight do
    if OS.mac?
      system_command "/usr/bin/xattr", args: ["-dr", "com.apple.quarantine", "#{staged_path}/ofga"]
    end
  end
end

The postflight hook is required because our darwin binaries aren't notarized and Homebrew quarantines cask downloads — without it macOS Gatekeeper blocks the binary on first run.

Not verified on a Mac. The cask generation, config validation and Homebrew behaviour above are all read from generated output and Homebrew's source; I have no macOS/brew available. Worth one brew install sergiught/tap/ofga on a Mac after the first release on this config, and confirming an existing formula install migrates on brew update.

📋 Checklist

• 🧪 Tests added or updated where it makes sense — n/a, build config; verified by generating the cask
• 📖 Docs updated — packaging/README.md now points at Casks/ofga.rb and the new migrations file; user-facing install docs need no change
• 🏷 PR title follows Conventional Commits
• 🟢 make check passes locally — n/a, no Go code touched