FEATURE: Count Pitchfork worker timeouts in Prometheus

plugin.rb

@@ -53,6 +53,16 @@ module ::DiscoursePrometheus
 
   on(:image_processing_finished) { |payload| image_processing_reporter.report(payload) }
 
+  on(:web_worker_timeout) do
+    metric = DiscoursePrometheus::InternalMetric::Custom.new
+    metric.type = "Counter"
+    metric.name = "pitchfork_worker_timeouts_total"
+    metric.description = "Total number of Pitchfork soft worker timeouts"
+    metric.value = 1
+
+    $prometheus_client.send_json_sync(metric.to_h)
+  end
+
   register_demon_process(DiscoursePrometheus::CollectorDemon)
   register_demon_process(DiscoursePrometheus::GlobalReporterDemon)
 

spec/lib/worker_timeout_spec.rb

@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+require "prometheus_exporter/server"
+require_relative "../../lib/collector"
+
+RSpec.describe DiscoursePrometheus do
+  describe ":web_worker_timeout" do
+    it "increments the timeout counter through the shared client" do
+      collector = DiscoursePrometheus::Collector.new
+      allow($prometheus_client).to receive(:send_json_sync) do |metric|
+        collector.process(Oj.dump(metric, mode: :object))
+      end
+
+      2.times { DiscourseEvent.trigger(:web_worker_timeout) }
+
+      expect(collector.prometheus_metrics_text).to include(
+        "pitchfork_worker_timeouts_total counter",
+        "pitchfork_worker_timeouts_total 2",
+      )
+    end
+  end
+end