Honor appsignal_name in Delayed Job enqueue title

The invoke side already lets a Delayed Job payload override its action
name with an `appsignal_name` method. Honor that same override when
titling the `enqueue.delayed_job` event, so the enqueue and perform
events stay tied to the same name.

The override is a full action name, so an enqueue that uses it reads as
`enqueue Class#method job` rather than the bare `enqueue Class job` we
use otherwise. We accept that inconsistency for the rare job that sets
it, since keeping the enqueue and perform names aligned matters more
than the title's shape.

Author: unflxw

lib/appsignal/integrations/delayed_job_plugin.rb

@@ -32,11 +32,25 @@ def self.enqueue_with_instrumentation(job, block)
           return block.call(job)
         end
 
-        Appsignal.instrument("enqueue.delayed_job", "enqueue #{job.name} job") do
+        Appsignal.instrument("enqueue.delayed_job", "enqueue #{enqueue_name(job)} job") do
           block.call(job)
         end
       end
 
+      # Titles the enqueue event after the job. The `appsignal_name` override is
+      # honored verbatim, as it is when naming the perform action. That override
+      # is a full action name, so an enqueue that uses it reads as
+      # `enqueue Class#method job` rather than the bare `enqueue Class job`. We
+      # accept that inconsistency so the enqueue and perform events stay tied to
+      # the same name for the rare job that sets it.
+      def self.enqueue_name(job)
+        payload = job.payload_object
+        appsignal_name = extract_value(payload, :appsignal_name, nil)
+        return appsignal_name if appsignal_name.is_a?(String)
+
+        job.name
+      end
+
       def self.invoke_with_instrumentation(job, block)
         transaction =
           Appsignal::Transaction.create(Appsignal::Transaction::BACKGROUND_JOB)

spec/lib/appsignal/integrations/delayed_job_plugin_spec.rb

@@ -48,6 +48,30 @@ def perform_job(job)
         end
       end
 
+      context "with a custom appsignal_name" do
+        before do
+          stub_const("DelayedNamedJob", Class.new do
+            def perform
+            end
+
+            def appsignal_name
+              "CustomName#perform"
+            end
+          end)
+        end
+
+        it "titles the enqueue event with the custom name" do
+          start_agent
+          transaction = http_request_transaction
+          set_current_transaction(transaction)
+
+          Delayed::Job.enqueue(DelayedNamedJob.new)
+
+          event = transaction.to_h["events"].find { |e| e["name"] == "enqueue.delayed_job" }
+          expect(event["title"]).to eq("enqueue CustomName#perform job")
+        end
+      end
+
       context "without an active transaction" do
         it "is a transparent pass-through" do
           start_agent