Fix Activity boundary names

Follow-up to vercel#85155. Made a mistake in the context-passing logic.

Author: acdlite

packages/next/src/client/components/layout-router.tsx

@@ -348,7 +348,7 @@ function InnerLayoutRouter({
 }: {
   tree: FlightRouterState
   segmentPath: FlightSegmentPath
-  debugNameContext: ActivityProps['name']
+  debugNameContext: string
   cacheNode: CacheNode
   params: Params
   url: string
@@ -584,7 +584,7 @@ export default function OuterLayoutRouter({
     parentParams,
     url,
     isActive,
-    debugNameContext: parentDebugNameContext,
+    debugNameContext,
   } = context
 
   // Get the CacheNode for this segment by reading it from the parent segment's
@@ -706,9 +706,9 @@ export default function OuterLayoutRouter({
 
     const debugName = getBoundaryDebugNameFromSegment(segment)
     // `debugNameContext` represents the nearest non-"virtual" parent segment.
-    // `getBoundaryDebugNameFromSegment` returns null for virtual segments.
-    // So if `debugName` is null, the context is passed through unchanged.
-    const debugNameContext = debugName ?? parentDebugNameContext
+    // `getBoundaryDebugNameFromSegment` returns undefined for virtual segments.
+    // So if `debugName` is undefined, the context is passed through unchanged.
+    const childDebugNameContext = debugName ?? debugNameContext
 
     // TODO: The loading module data for a segment is stored on the parent, then
     // applied to each of that parent segment's parallel route slots. In the
@@ -742,7 +742,7 @@ export default function OuterLayoutRouter({
                       params={params}
                       cacheNode={cacheNode}
                       segmentPath={segmentPath}
-                      debugNameContext={debugNameContext}
+                      debugNameContext={childDebugNameContext}
                       isActive={isActive && stateKey === activeStateKey}
                     />
                     {segmentBoundaryTriggerNode}

packages/next/src/shared/lib/app-router-context.shared-runtime.ts

@@ -63,7 +63,7 @@ export const LayoutRouterContext = React.createContext<{
   parentCacheNode: CacheNode
   parentSegmentPath: FlightSegmentPath | null
   parentParams: Params
-  debugNameContext: string | undefined
+  debugNameContext: string
   url: string
   isActive: boolean
 } | null>(null)