warp_engine 0.2.0: pluggable storage adapter and publish notifications

Two seams the hosts needed, both backward compatible.

Storage: artifacts are served through WarpEngine::Storage.adapter instead of
raw filesystem calls. The default :local adapter keeps the previous behaviour
byte for byte, including the path traversal guard. A host can now set
config.storage_adapter to any object answering file?/directory?/locate and
serve builds from an object store - FileService and /api/download both honour
a Location.redirect, so a signing adapter turns them into redirects.
DownloadService#create still returns an absolute path (nil when missing) for
existing callers; #locate is the new entry point that can also return a
redirect. Ingestion (upload, extraction, file manager) stays local for now.

Publish: PublishService emits ActiveSupport::Notifications
("warp_engine.publish") with platform/name/version/software/release, so hosts
can react to a new build without hanging callbacks on the models.
WarpEngine.instruments_publish? lets a host feature-detect and keep its
fallback for older engine versions.

spec/services/publish_service_spec.rb

@@ -55,5 +55,38 @@ RSpec.describe WarpEngine::PublishService do
 
       expect(mock_service).to have_received(:update).with("game", "1.0")
     end
+    describe "instrumentation" do
+      let(:input) { WarpEngine::PublishInputDto.new(platform: "tic80", name: "game", version: "1.0") }
+      let(:release) { WarpEngine::Release.new(version: "1.0") }
+
+      before do
+        mock_service = instance_double(WarpEngine::Platforms::Tic80::Service, update: release)
+        allow(WarpEngine::Platforms::Tic80::Service).to receive(:new).and_return(mock_service)
+      end
+
+      # The host reacts to a new build through this event instead of hanging a
+      # callback on the Release model.
+      it "emits warp_engine.publish with the release in the payload" do
+        payloads = []
+        ActiveSupport::Notifications.subscribe(described_class::NOTIFICATION) do |*, payload|
+          payloads << payload
+        end
+
+        described_class.new.publish(input)
+
+        expect(payloads.size).to eq(1)
+        expect(payloads.first).to include(platform: "tic80", name: "game", version: "1.0", release: release)
+      ensure
+        ActiveSupport::Notifications.unsubscribe(described_class::NOTIFICATION)
+      end
+
+      it "returns the release" do
+        expect(described_class.new.publish(input)).to eq(release)
+      end
+
+      it "advertises the feature so older hosts can feature-detect" do
+        expect(WarpEngine.instruments_publish?).to be(true)
+      end
+    end
   end
 end