feat(rxjava3): add RxJava 3 context propagation instrumentation

[wconti27]

🤖 Generated with APM Instrumentation Toolkit

What Does This Do

Adds instrumentation for RxJava 3 (io.reactivex.rxjava3:rxjava) — context propagation across async reactive subscription boundaries for all 5 reactive types.

Motivation

Customer request for RxJava 3 support. RxJava 2 instrumentation already exists; this extends coverage to the v3 API which uses a new package namespace (io.reactivex.rxjava3.core).

Additional Notes

Design: Context propagation only — no new spans created. Mirrors the existing rxjava-2.0 module exactly:

• Hooks each reactive type's constructor (capture active context) and subscribe() (wrap observer with tracing wrapper)
• Observable, Flowable, Single, Completable, Maybe — all 5 types instrumented
• Flowable handles two subscribe() overloads: subscribe(Subscriber) and subscribe(FlowableSubscriber) — the latter is new in RxJava 3 and shares a single Advice class via DYNAMIC typing + TracingSubscriber implementing both interfaces
• RxJava3AsyncResultExtension — equivalent of RxJavaAsyncResultExtension in rxjava-2.0, extends spans until reactive chains complete for @WithSpan-annotated methods

Known limitation: Context propagation through Maybe.delay() (computation scheduler) does not produce child spans in the current implementation — the delayed Flowable tests provide equivalent delay coverage. Tracked as a follow-up investigation.

Contributor Checklist

• Format the title according to the contribution guidelines
• Assign the type: and (comp: or inst:) labels in addition to any other useful labels

Jira ticket: [PROJ-IDENT]

🤖 Generated with APM Instrumentation Toolkit

[dd-octo-sts]

🟢 Java Benchmark SLOs — All performance SLOs passed

Suite	Status
Startup	🟢 pass

SLO thresholds are defined here based on automatically generated metrics. A warning is raised when results are within 5% of the threshold.

PR vs. master results

Scenario	Candidate	master	Δ (95% CI of mean)
startup:insecure-bank:iast:Agent	13.94 s	13.90 s	[-0.8%; +1.3%] (no difference)
startup:insecure-bank:tracing:Agent	12.82 s	12.97 s	[-2.5%; +0.1%] (no difference)
startup:petclinic:appsec:Agent	16.63 s	16.60 s	[-1.1%; +1.5%] (no difference)
startup:petclinic:iast:Agent	16.66 s	16.62 s	[-1.1%; +1.5%] (no difference)
startup:petclinic:profiling:Agent	16.58 s	16.57 s	[-1.6%; +1.6%] (no difference)
startup:petclinic:tracing:Agent	15.80 s	15.79 s	[-1.6%; +1.8%] (no difference)

Commit: 66ab94b7 · CI Pipeline · Benchmarking Platform UI

---

Load and DaCapo benchmarks can be triggered manually in the GitLab pipeline. Results will appear in the Benchmarking Platform UI after completion.