Merge pull request 'Run trusted gem releases only on GitHub' (#1) from fix/github-only-release-runner-guard-20260719 into main

.github/workflows/release.yml

@@ -7,6 +7,7 @@ on:
 
 jobs:
   push:
+    if: ${{ github.server_url == 'https://github.com' }}
     runs-on: ubuntu-latest
     permissions:
       contents: write

test/release_workflow_test.rb

@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+require "minitest/autorun"
+require "yaml"
+
+class ReleaseWorkflowTest < Minitest::Test
+  ROOT = File.expand_path("..", __dir__)
+  WORKFLOW_PATH = File.join(ROOT, ".github", "workflows", "release.yml")
+
+  def workflow
+    @workflow ||= YAML.safe_load(File.read(WORKFLOW_PATH), aliases: false)
+  end
+
+  def push_job
+    workflow.fetch("jobs").fetch("push")
+  end
+
+  def test_release_job_is_inert_on_non_github_runners
+    assert_equal "${{ github.server_url == 'https://github.com' }}", push_job.fetch("if")
+  end
+
+  def test_release_job_keeps_the_trusted_publisher_boundary
+    assert_equal "release", push_job.fetch("environment")
+    assert_equal(
+      { "contents" => "write", "id-token" => "write" },
+      push_job.fetch("permissions")
+    )
+
+    steps = push_job.fetch("steps")
+    assert_equal 1, steps.count { |step| step["uses"] == "rubygems/release-gem@v1" }
+    refute steps.any? { |step| step.fetch("run", "").match?(/\bgem\s+push\b/) }
+  end
+end