fix: correct render start time

Author: bbrzoska

src/v3/hooks.ts

@@ -61,13 +61,8 @@ export const generateUseBeacon =
 
     traceManager.processSpan(renderStartTaskEntry)
 
-    // React's concurrent rendering might pause and discard a render,
-    // which would mean that an effect scheduled for that render does not execute because the render itself was not committed to the DOM.
-    // we want to store the first time that the render was scheduled as the start time of rendering
     const renderStartRef = useRef<Timestamp | undefined>()
-    if (!renderStartRef.current) {
-      renderStartRef.current = renderStartTaskEntry.startTime
-    }
+    renderStartRef.current = renderStartTaskEntry.startTime
 
     // Beacon effect for tracking 'component-render'. This will fire after every render as it does not have any dependencies:
     useEffect(() => {

src/v3/recordingComputeUtils.ts

@@ -229,7 +229,9 @@ function getComputedRenderBeaconSpans<
 
       if (entry.span.type === 'component-render') {
         spanTimes.renderCount += 1
-        // If there was a pending render start, include the time from that start to this render
+        // React's concurrent rendering might pause and discard a render,
+        // which would mean that an effect scheduled for that render does not execute because the render itself was not committed to the DOM.
+        // we want to extend the the render span backwards, to first time that rendering was scheduled as the start time of rendering
         if (spanTimes.lastRenderStartTime !== undefined) {
           spanTimes.sumOfDurations +=
             start + duration - spanTimes.lastRenderStartTime