Ensure childSpans is always initialized to prevent undefined access

Initialize childSpans to empty array for all spans when they're created in
transform-trace-data, before the tree walk. This ensures childSpans is always
defined as per the Span type definition (childSpans: Array<Span>).

Previously, childSpans was only populated during tree walk, which could leave
it undefined for spans not in the tree or in edge cases. This violated the
type contract and required defensive null checks in consuming code.

Also removed unnecessary null check in sanitizeOverFlowingChildren since
childSpans is now guaranteed to be defined.

This fixes the issue where childSpans could be undefined despite being typed
as a required array.

Co-authored-by: yurishkuro <3523016+yurishkuro@users.noreply.github.com>

Author: Copilot

packages/jaeger-ui/src/components/TracePage/CriticalPath/utils/sanitizeOverFlowingChildren.tsx

@@ -89,7 +89,7 @@ const sanitizeOverFlowingChildren = (spanMap: Map<string, Span>): Map<string, Sp
   // Second pass: filter out dropped children from childSpans arrays
   const finalSpanMap = new Map<string, Span>();
   newSpanMap.forEach((span, spanId) => {
-    const filteredChildSpans = (span.childSpans || []).filter(child => !droppedSpanIds.has(child.spanID));
+    const filteredChildSpans = span.childSpans.filter(child => !droppedSpanIds.has(child.spanID));
 
     // Update child span references with sanitized parent
     let updatedReferences = span.references;

packages/jaeger-ui/src/model/transform-trace-data.tsx

@@ -101,6 +101,7 @@ export default function transformTraceData(data: TraceData & { spans: SpanData[]
       spanIdCounts.set(spanID, 1);
     }
     span.process = data.processes[processID];
+    span.childSpans = []; // Initialize to empty array, will be populated during tree walk
     spanMap.set(spanID, span);
   }
   // tree is necessary to sort the spans, so children follow parents, and