✨ Report update loops throttled by the update scheduler

When the scheduler throttles an update loop, it only logs a console
warning, so a loop that no longer crashes leaves no trace. Send an
error report too, with the events in flight and the last events, at
most once per report window.

Relates to #12580

AI-assisted-by: claude-opus-5-5

frontend/src/app/main/errors.cljs

@@ -438,17 +438,30 @@
   (volatile! 0))
 
 (defn on-update-loop
-  "Handler for the rumext update scheduler trips: logs the throttled
-  update loop with the events being processed, at most once per
+  "Handler for the rumext update scheduler trips: logs and reports the
+  throttled update loop with the events being processed, at most once per
   `report-window-ms`. Runs inside store watchers and effect bodies, so it
   never throws."
-  [_]
+  [{:keys [rounds]}]
   (try
     (let [now (inst-ms (ct/now))]
       (when (>= (- now @update-loop-warned-at) report-window-ms)
         (vreset! update-loop-warned-at now)
-        (.warn js/console "[update-scheduler] update loop throttled; in-flight events:"
-               (into-array (map ptk/repr-event (ptk/in-flight-events st/state))))))
+        (let [events (ptk/in-flight-events st/state)
+              cause  (ex-info "update loop throttled"
+                              {:type :internal
+                               :code :update-loop-throttled
+                               :rounds rounds})]
+          (.warn js/console "[update-scheduler] update loop throttled; in-flight events:"
+                 (into-array (map ptk/repr-event events)))
+          (when (seq events)
+            (.set in-flight-by-cause cause (in-flight-lines events)))
+          ;; Report outside the loop that tripped the scheduler
+          (ts/schedule
+           #(submit-report :event-name "handled-exception"
+                           :hint (ex-message cause)
+                           :report (fn [] (generate-report cause))
+                           :cause cause)))))
     (catch :default _
       nil)))
 

frontend/test/frontend_tests/main_errors_test.cljs

@@ -14,7 +14,8 @@
     - events in flight            – the full report lists the events the
       store was processing when it caught the exception; a failing stream
       pipeline lists the emitters of the value, not its own event
-    - on-update-loop              – never throws into the scheduler's caller
+    - on-update-loop              – never throws into the scheduler's caller;
+      reports the throttled loop with the events in flight
     - flash schedules async report and toast – neither the report nor
       ntf/show is emitted synchronously
     - organization SSO recovery   – expired SSO sessions go back to the provider
@@ -554,6 +555,28 @@
      {ptk/in-flight-events (fn [_] (throw (js/Error. "in-flight read failure")))}
      (t/is (nil? (errors/on-update-loop {:rounds 26}))))))
 
+(t/deftest ^:async update-loop-is-reported-with-the-events-in-flight
+  (errors/reset-report-governor!)
+  (vreset! @#'errors/update-loop-warned-at 0)
+  (let [events (atom [])
+        loop-ev (ptk/reify ::test-update-loop-source)]
+    (await
+     (mock/with-mocks*
+       {st/emit!              (mock/stub (fn [& emitted] (swap! events into emitted)))
+        ptk/in-flight-events  (fn [_] [loop-ev])
+        st/format-last-events (mock/stub (fn [& _] "(stub last events)"))
+        rt/get-current-href   (constantly "https://penpot.example.com/#/workspace")
+        tm/schedule           (mock/stub (fn [f] (f)))}
+       (errors/on-update-loop {:rounds 26})
+       ;; A second trip within the window is not reported again
+       (errors/on-update-loop {:rounds 26})
+       (t/is (= 1 (count @events)))
+       (let [props (deref (first @events))]
+         (t/is (= "handled-exception" (::ev/name props)))
+         (t/is (= "update loop throttled" (:hint props)))
+         (t/is (str/includes? (in-flight-section (:report props))
+                              "test-update-loop-source")))))))
+
 ;; ---------------------------------------------------------------------------
 ;; Expired organization SSO session
 ;;