fix(nextjs): Also recognize a prerender span that is activated by its caller

Next.js starts its spans through `startActiveSpan`, which the tracer wrapper
marks on the context. A span started through `startSpan` and set on a context
by the caller takes a different path, so the wrapper remembers those spans and
the propagator checks the span on the context too.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

Author: chargome

packages/nextjs/src/server/nextSentryPropagator.ts

@@ -1,5 +1,5 @@
-import type { Context, SpanOptions, TextMapSetter, Tracer, TracerProvider } from '@opentelemetry/api';
-import { context, createContextKey, propagation } from '@opentelemetry/api';
+import type { Context, Span, SpanOptions, TextMapSetter, Tracer, TracerProvider } from '@opentelemetry/api';
+import { context, createContextKey, propagation, trace } from '@opentelemetry/api';
 import { SentryPropagator } from '@sentry/opentelemetry';
 import { ATTR_NEXT_SPAN_NAME, ATTR_NEXT_SPAN_TYPE } from '../common/nextSpanAttributes';
 
@@ -8,6 +8,9 @@ const PRERENDER_ROUTE_SPAN_NAME_PREFIX = 'prerender route';
 
 const PRERENDER_CONTEXT_KEY = createContextKey('sentry.nextjs.prerender');
 
+// Prerender spans started with `startSpan`, which the caller activates on a context of its own.
+const prerenderSpans = new WeakSet<Span>();
+
 /**
  * Whether these are the start arguments of the span Next.js wraps a prerender in. Next.js computes the
  * `sentry-trace` and `baggage` meta tags of a document inside that span, and a prerender produces a
@@ -26,7 +29,11 @@ export function isPrerenderSpanStart(name: string, options: SpanOptions | undefi
 
 /** Whether the context belongs to a prerender started through a tracer of a wrapped provider. */
 export function isPrerenderContext(ctx: Context): boolean {
-  return ctx.getValue(PRERENDER_CONTEXT_KEY) === true;
+  if (ctx.getValue(PRERENDER_CONTEXT_KEY) === true) {
+    return true;
+  }
+  const span = trace.getSpan(ctx);
+  return !!span && prerenderSpans.has(span);
 }
 
 /**
@@ -37,7 +44,13 @@ export function isPrerenderContext(ctx: Context): boolean {
  */
 function wrapTracer(tracer: Tracer): Tracer {
   return {
-    startSpan: (name, options, ctx) => tracer.startSpan(name, options, ctx),
+    startSpan: (name, options, ctx) => {
+      const span = tracer.startSpan(name, options, ctx);
+      if (isPrerenderSpanStart(name, options)) {
+        prerenderSpans.add(span);
+      }
+      return span;
+    },
     startActiveSpan: (name: string, ...args: unknown[]) => {
       const startActiveSpan = tracer.startActiveSpan.bind(tracer) as (name: string, ...args: unknown[]) => unknown;
       const options = typeof args[0] === 'function' ? undefined : (args[0] as SpanOptions | undefined);

packages/nextjs/test/server/nextSentryPropagator.test.ts

@@ -114,6 +114,21 @@ describe('NextSentryPropagator', () => {
     });
   });
 
+  it('recognizes a prerender span that was started inactive and activated by the caller', () => {
+    const span = trace.getTracer('next.js').startSpan('prerender route (app) /[id]', PRERENDER_SPAN_OPTIONS);
+    context.with(trace.setSpan(context.active(), span), () => {
+      expect(isPrerenderContext(context.active())).toBe(true);
+      expect(inject()).toEqual({});
+    });
+    span.end();
+
+    const renderSpan = trace.getTracer('next.js').startSpan('render route (app) /blocking', RENDER_SPAN_OPTIONS);
+    context.with(trace.setSpan(context.active(), renderSpan), () => {
+      expect(inject()['sentry-trace']).toBeDefined();
+    });
+    renderSpan.end();
+  });
+
   it('marks an explicitly passed context', () => {
     trace
       .getTracer('next.js')