Check the version API before downloading a release

lib/bake/gem/github/publisher.rb

@@ -33,7 +33,7 @@ def build(number)
 						return output(receipt, restored: true)
 					end
 					filename = "#{evidence.fetch(:name)}-#{evidence.fetch(:version)}.gem"
-					if registry_digest(filename)
+					if registry_digest(evidence.fetch(:name), evidence.fetch(:version))
 						raise "Version is already published but this run has no retained artifact. Restore the original artifact; do not rebuild."
 					end
 					package = build_package(path)
@@ -63,14 +63,14 @@ def publish(number)
 					system("gh", "attestation", "verify", package, "--repo", @repository, "--bundle", File.join(@root, "pkg", "provenance.sigstore.json"), "--signer-workflow", "#{@repository}/.github/workflows/release-publish.yaml", "--source-digest", receipt.fetch(:commit), "--deny-self-hosted-runners", chdir: @root)
 					tag = "v#{receipt.fetch(:version)}"
 					guard_tag(tag, receipt.fetch(:commit))
-					remote_digest = registry_digest(receipt.fetch(:file))
+					remote_digest = registry_digest(receipt.fetch(:name), receipt.fetch(:version))
 					if remote_digest
 						raise "Published version has different bytes." unless remote_digest == receipt.fetch(:sha256)
 					else
 						gem_command("push", package, "--host", "https://rubygems.org", "--attestation", bundle)
 					end
 					# A failed read after upload is recoverable by rerunning the same workflow.
-					raise "Registry artifact does not match; retry after registry propagation." unless registry_digest(receipt.fetch(:file)) == receipt.fetch(:sha256)
+					raise "Registry artifact does not match; retry after registry propagation." unless registry_digest(receipt.fetch(:name), receipt.fetch(:version)) == receipt.fetch(:sha256)
 					attestations = registry_get("https://rubygems.org/api/v1/attestations/#{receipt.fetch(:name)}-#{receipt.fetch(:version)}.json")
 					raise "Registry attestation is missing." unless attestations
 					registry_bundles = JSON.parse(attestations)
@@ -193,10 +193,12 @@ def provenance(receipt)
 					}
 				end
 
-				def registry_digest(filename)
-					if body = registry_get("https://rubygems.org/downloads/#{filename}")
-						Digest::SHA256.hexdigest(body)
-					end
+				def registry_digest(name, version)
+					# Missing downloads can return 403; use the version API to establish absence.
+					return nil unless registry_get("https://rubygems.org/api/v2/rubygems/#{name}/versions/#{version}.json?platform=ruby")
+					body = registry_get("https://rubygems.org/downloads/#{name}-#{version}.gem")
+					raise "Published gem download is missing; retry after registry propagation." unless body
+					Digest::SHA256.hexdigest(body)
 				end
 
 				def registry_get(url, redirects: 5)

test/recovery.rb

@@ -53,7 +53,7 @@ def api(path)
 	def guard_environment
 	end
 
-	def registry_digest(filename)
+	def registry_digest(name, version)
 		@remote_digest
 	end
 

test/registry.rb

@@ -0,0 +1,65 @@
+# frozen_string_literal: true
+
+# Released under the MIT License.
+# Copyright, 2026, by Samuel Williams.
+
+require_relative "../lib/bake/gem/github/publisher"
+
+describe Bake::Gem::GitHub::Publisher do
+	with "#registry_digest" do
+		let(:publisher) {subject.allocate}
+		let(:http) {Object.new}
+		let(:responses) {{}}
+		let(:version_path) {"/api/v2/rubygems/example/versions/1.0.1.json?platform=ruby"}
+		let(:download_path) {"/downloads/example-1.0.1.gem"}
+
+		def response(code, body = "")
+			result = Net::HTTPResponse::CODE_TO_OBJ.fetch(code).new("1.1", code, "")
+			mock(result) do |wrapper|
+				wrapper.replace(:body){body}
+			end
+			result
+		end
+
+		before do
+			mock(http) do |wrapper|
+				wrapper.replace(:get){|path| responses.fetch(path)}
+			end
+			mock(Net::HTTP) do |wrapper|
+				wrapper.replace(:start) do |*arguments, **options, &block|
+					block.call(http)
+				end
+			end
+		end
+
+		it "recognizes an unpublished version without requesting the missing download" do
+			responses[version_path] = response("404")
+			expect(publisher.send(:registry_digest, "example", "1.0.1")).to be_nil
+		end
+
+		it "hashes the actual published package bytes" do
+			responses[version_path] = response("200", "{}")
+			responses[download_path] = response("200", "gem bytes\x00\xff".b)
+			expect(publisher.send(:registry_digest, "example", "1.0.1")).to be == Digest::SHA256.hexdigest("gem bytes\x00\xff".b)
+		end
+
+		["403", "500"].each do |code|
+			it "rejects version API errors", unique: code do
+				responses[version_path] = response(code)
+				expect{publisher.send(:registry_digest, "example", "1.0.1")}.to raise_exception(RuntimeError, message: be == "Registry request failed: #{code}")
+			end
+		end
+
+		it "rejects a forbidden download for an existing version" do
+			responses[version_path] = response("200", "{}")
+			responses[download_path] = response("403")
+			expect{publisher.send(:registry_digest, "example", "1.0.1")}.to raise_exception(RuntimeError, message: be == "Registry request failed: 403")
+		end
+
+		it "rejects a missing download for an existing version" do
+			responses[version_path] = response("200", "{}")
+			responses[download_path] = response("404")
+			expect{publisher.send(:registry_digest, "example", "1.0.1")}.to raise_exception(RuntimeError, message: be =~ /Published gem download is missing/)
+		end
+	end
+end