[jamescrosswell]

Summary

SentryPropagator.Extract mapped a sentry-trace header with no sampling flag (<trace>-<span>, the deferred form) to ActivityTraceFlags.None. OpenTelemetry's default ParentBasedSampler sends a remote parent without Recorded to AlwaysOff, so a service using the propagator dropped all spans for requests from upstream SDKs that hadn't made a sampling decision, and propagated -0 further downstream.

Now only an explicit -0 maps to unsampled; a missing flag becomes Recorded. This is option 1 from the issue and matches sentry-java's OpenTelemetryOtlpPropagator.

Notes for review

• Trade-off called out in the issue: with the default ParentBasedSampler, deferred requests are now always recorded, so a ratio-based root sampler is not consulted for them. Option 2 (marking the deferred case and shipping a sampler that delegates to the root sampler) would respect it but adds public API; it can follow separately if we want it.
• SentryPropagator.cs is also compiled into the obsolete Sentry.OpenTelemetry package, where AddSentry() registers it. There, SentrySpanProcessor passes a remote parent's Recorded flag to Hub.StartTransaction as the sampling decision, which takes precedence over TracesSampleRate (a TracesSampler still runs first). Deferred requests used to be dropped even at TracesSampleRate = 1.0; they now become transactions even at 0. sentry-java's span-processor mode runs its own sampler for a deferred parent instead.

Fixes #5903

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.98%. Comparing base (25b505e) to head (eb004d7).
⚠️ Report is 2 commits behind head on version7.

Additional details and impacted files

@@            Coverage Diff            @@
##           version7    #5907   +/-   ##
=========================================
  Coverage     76.98%   76.98%           
=========================================
  Files           538      538           
  Lines         19714    19714           
  Branches       3872     3872           
=========================================
+ Hits          15176    15177    +1     
- Misses         3666     3667    +1     
+ Partials        872      870    -2     

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[ric-oliv]

There's one case this PR doesn't cover, and I think it's fine to follow up on it separately. A service with SentryPropagator still drops its spans when a sentry-trace without a flag comes with a traceparent of 00-<trace>-<span>-00. That's what the .NET SDK sends when there's no active span and PropagateTraceparent is on, see W3CTraceparentHeader. The JS SDK sends -00 in the same situation, see generateTraceparentHeader.

ASP.NET Core starts the request activity from traceparent, and the default ParentBasedSampler drops it. OpenTelemetry's ASP.NET Core instrumentation only replaces that activity when the trace ID, span ID or tracestate differ, see HttpInListener. It doesn't compare the flags, so when the IDs match and there's no tracestate, it never uses what SentryPropagator returns.

[jamescrosswell]

Thanks, confirmed. Tracking it separately in #5910, with a few options for fixing it.

🤖 Addressed by Claude Code