fix(release): stop the Homebrew cask's postflight deprecation warning

[ftarasenko]

Every brew command touching the cask printed:

Warning: Calling `postflight` is deprecated! Use `postflight_steps` instead.

The stanza is the cask's quarantine strip, which the unsigned binary needs in order to launch on macOS, so it cannot simply be dropped — and Homebrew deprecations become hard errors a few releases later.

What changed

GoReleaser renders homebrew_casks.hooks.post.install as postflight do … end and cannot emit the *_steps stanzas yet (goreleaser/goreleaser#6870, PR #6873, milestone v2.19.0). It also has no way to emit both spellings, so .goreleaser.yaml now writes the stanza itself through custom_block, and the cask picks one at load time:

steps_dsl = defined?(Homebrew::InstallSteps::DSL) && Homebrew::InstallSteps::DSL
if steps_dsl && steps_dsl.method_defined?(:run) && steps_dsl.method_defined?(:on_macos)
  postflight_steps do
    on_macos do
      run "/usr/bin/xattr",
          args: ["-dr", "com.apple.quarantine", "{{staged_path}}/koc"]
    end
  end
else
  postflight do
    if OS.mac?
      system_command "/usr/bin/xattr",
        args: ["-dr", "com.apple.quarantine", "#{staged_path}/koc"]
    end
  end
end

The cask installs on every Homebrew version and prints a deprecation warning on none.

Why the probe is what it is

Three Homebrew releases matter, and they are not the same one:

Homebrew	change
6.0.0	postflight_steps stanza lands
6.0.13	steps DSL gains run / on_macos — the steps this block calls
6.0.16	postflight deprecated (the warning)

So the probe asks Homebrew::InstallSteps::DSL.method_defined?(:run) rather than respond_to?(:postflight_steps): the latter is true on 6.0.0–6.0.12, where the block body would then die. (Cask::DSL#respond_to_missing? returns false, so respond_to? is a sound probe in principle — it just answers the wrong question here.)

Two more details, both spelled out next to the block in .goreleaser.yaml:

• {{staged_path}} is written escaped as {{ "{{staged_path}}" }} because GoReleaser runs the whole generated cask through its own template engine as a final pass. The legacy branch spells the same path #{staged_path}, since the steps DSL has no Ruby interpolation — that was the point of deprecating postflight.
• custom_block is injected right after cask "koc" do, so the generated file's stanza order is unconventional. It is still correct: Homebrew orders artifacts by class (Binary before PostflightSteps, per Cask::Artifact::AbstractArtifact.sort_order), never by file position.

Verification

• goreleaser check clean; cask regenerated with GoReleaser built from source (main, since no released version carries the fix) via a snapshot release — both branches render, {{staged_path}} and #{staged_path} each survive the template pass, ruby -c clean.
• The emitted block was evaluated against stub DSLs for all three Homebrew generations:

pre-6.0 (no InstallSteps)    picked=postflight         PASS
6.0.0-6.0.12 (no run step)   picked=postflight         PASS
6.0.13+ (run + on_macos)     picked=postflight_steps   PASS
                             run -> ["/usr/bin/xattr", ["-dr", "com.apple.quarantine", "{{staged_path}}/koc"]]

No Go code changes, so the command surface is unchanged and docs/coverage.md needs no update. README and AGENTS.md record the version boundaries and the reasoning.

The tap keeps serving the v0.32.0 cask until a new tag is cut.

🤖 Generated with Claude Code

https://claude.ai/code/session_0122vGrcATX7433WuQ91iLm9

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