Span streaming drops continued traces without baggage: empty frozen DSC leads to missing_dsc (breaks Uptime check traces) #25243

Is there an existing issue for this?

• I have checked for existing issues https://github.com/getsentry/sentry-javascript/issues
• I have reviewed the documentation https://docs.sentry.io/
• I am using the latest SDK release https://github.com/getsentry/sentry-javascript/releases

How do you use Sentry?

Sentry Saas (sentry.io)

Which SDK are you using?

@sentry/node

SDK Version

11.6.0

Framework Version

Node.js 24.21.0 (first seen in production with @sentry/nestjs 11.0.0 on Fastify and @sentry/react-router 11.0.0)

Link to Sentry event

No response

Reproduction Example/SDK Setup

import http from 'node:http';
import * as Sentry from '@sentry/node';

Sentry.init({
  dsn: 'https://public@o123.ingest.de.sentry.io/1',
  tracesSampleRate: 1,
  transport: (options) => Sentry.createTransport(options, () => Promise.resolve({ statusCode: 200 })),
});
Sentry.getClient().on('beforeEnvelope', ([header, items]) => {
  if (items.some(([item]) => item.type === 'span')) console.log(header.trace ? 'trace header present' : 'NO trace header');
});

const server = http.createServer((req, res) => res.end('ok'));
server.listen(0, async () => {
  await fetch(`http://127.0.0.1:${server.address().port}/`, {
    headers: { 'sentry-trace': `${'a'.repeat(32)}-${'b'.repeat(16)}-1` },
  });
  await Sentry.flush(2000);
  server.close();
});

Steps to Reproduce

1. Run the script above with @sentry/node 11.6.0 (default traceLifecycle: 'stream').
2. It sends one request to its own server with a sampled sentry-trace header and no baggage header.
3. Look at the logged envelope headers: the envelope with the incoming request's spans has no trace header. (The second envelope belongs to the outgoing fetch, which starts its own trace.)
4. Add strictTraceContinuation: true to Sentry.init and run it again: now that envelope has a trace header.

Expected Result

Spans of a request that continues a trace from a sentry-trace header without baggage reach Sentry, as the equivalent transactions did with SDK 10. For example the SDK could fill the DSC from the client (trace_id, public_key) in stream mode, Relay could accept such span envelopes, or the uptime checker could send baggage.

Actual Result

The span envelope of the incoming request goes out without a trace header, and Relay drops it. The org stats show those spans with outcome invalid, reason missing_dsc.

In production this hits Sentry Uptime monitoring: an uptime check on a readiness endpoint (trace sampling on) reaches two Node services every five minutes and gets a 200, but since the upgrade every span of those requests is dropped as missing_dsc (12 spans per check in one project, 14 in the other). A request to the same endpoint without trace headers is traced and accepted end to end. The check's requests apparently carry sentry-trace without Sentry baggage.

Additional Context

Where it comes from, in @sentry/core 11.6.0:

• propagationContextFromHeaders (build/esm/utils/tracing.js) returns dsc: dynamicSamplingContext || {} when the traceparent has a trace id but no DSC came with it ("we are not head of trace and we must freeze it").
• createStreamedSpanEnvelope (build/esm/tracing/spans/envelope.js) adds the trace envelope header only when dscHasRequiredProps(dsc) holds, which needs trace_id and public_key.

Workaround: strictTraceContinuation: true. The spans arrive again, but the services no longer continue the uptime check's trace, so the check and its downstream spans end up in separate traces.

Priority

No response