Add dd-openfeature SDK exposure and flag evaluation pipelines

[PerfectSlayer]

What Does This Do

Adds the exposure and flag evaluation event pipelines to the dd-openfeature SDK: exposure deduplication (LRU cache), evaluation aggregation, payload building and batching over the connector event transport. Includes the JMH benchmarks.

Motivation

Event batching stays in the SDK; the agent only forwards payloads (APMLP-1512).

Additional Notes

The logic is ported almost entirely from the agent feature-flagging-lib / feature-flagging-bootstrap modules. Review carefully the two pipelines, now sending through the connector EventTransport instead of the agent EVP publisher, and the JSON serialization, moved from Moshi to hand-written Jackson streaming. Everything else is a package move.

New files

File	Notes
exposure/ExposuresRequestTest	Wire shape tests of the hand-written exposure JSON: serial_id present / zero / absent, context and subject attributes

Moved, package rename only (no logic change)

• exposure/Allocation, exposure/Flag, exposure/Subject, exposure/Variant, flagevaluation/FlagEvalEvent (from bootstrap datadog.trace.api.featureflag.*)
• exposure/ExposureEvent: also drops the 5-arg convenience constructor, serial_id is passed explicitly
• exposure/ExposureCache (from feature-flagging-lib)
• flagevaluation/FlagEvaluationAggregator: agent HashingUtils replaced by equivalent private helpers
• Tests: exposure/LRUExposureCacheTest (passes a null serial id), flagevaluation/FlagEvaluationAggregatorTest
• JMH: FlagEvaluationHotPathBenchmark, FlagEvaluationEnqueueContentionBenchmark, now building FlagEvaluationPipeline with a no-op EventTransport and HealthMetrics.NOOP instead of the agent Config / BackendApiFactory

Moved with significant changes

New file	Master origin	Changes
exposure/ExposurePipeline	lib ExposureWriterImpl	Posts to the exposures route through EventTransport instead of FeatureFlagEvpPublisher. Plain Consumer<ExposureEvent>, no gateway listener registration. SDK EventQueue replaces the JCTools queue, RuntimeServices.newThread replaces AgentThreadFactory. "EVP proxy unavailable" startup check removed. Dedup, batching and flush logic unchanged
exposure/ExposuresRequest	bootstrap exposure/ExposuresRequest	Same DTO plus serialize() with Jackson streaming (JsonWriting) instead of Moshi reflection; null subject.id, subject.attributes and serial_id omitted
exposure/LRUExposureCache	lib LRUExposureCache	Agent LRUCache replaced by an access-ordered LinkedHashMap
flagevaluation/FlagEvaluationPipeline	lib FlagEvaluationWriterImpl	Posts to the flagevaluation route through EventTransport; agentless / proxy fallback now lives in the transport. Health counters through RuntimeServices.countMetric instead of CoreMetricCollector. EventQueue and RuntimeServices.newThread replace JCTools and the agent thread. Gateway coupling (registration, enqueue gate, deregistration), EVP proxy fail-fast, error callback and test-only factories removed. Payload limit hard-coded to 5 MiB (was EvpProxy.PAYLOAD_SIZE_LIMIT_BYTES). Aggregation, final flush and drop accounting unchanged
flagevaluation/FlagEvaluationWriter	bootstrap flagevaluation/FlagEvaluationWriter	Narrowed to the producer API (enqueue, hasCapacityForEnqueue, countPreQueueOverflow, countContextTruncated); lifecycle moved to FlagEvaluationPipeline
flagevaluation/FlagEvaluationPayloads	lib FlagEvaluationPayloads	Moshi adapters and request DTO replaced by Jackson streaming (null optionals omitted). SHA-256 hashTargetingKey inlined from ULeb128Encoder, same algorithm
exposure/ExposurePipelineTest	lib ExposureWriterTests	Rewritten against a capturing EventTransport. Agentless, retry and EVP proxy tests dropped (now transport concerns). Added close, wire shape and non-finite attribute tests
flagevaluation/FlagEvaluationPipelineTest	lib FlagEvaluationWriterImplTest	Agent-only tests dropped (direct intake, gateway gate / consent / registration, EVP fail-fast, SCO constructor). Added non-finite context number serialization test
flagevaluation/FlagEvaluationTestSupport	lib FlagEvaluationTestSupport	Mockito BackendApi / OkHttp capture replaced by a CapturingTransport and RecordingMetrics; Moshi replaced by JsonReading

Shared files

• dd-openfeature/build.gradle.kts: applies dd-trace-java.jmh-conventions for the moved benchmarks

Stack

The full change is in #12709. It was split into this stack to ease the review.

1. Resolve Feature Flags enablement from instrumenter config #12845
2. Add dd-openfeature SDK flag configuration and evaluation core #12840
3. Add dd-openfeature SDK settings and configuration delivery #12841
4. Add dd-openfeature SDK exposure and flag evaluation pipelines #12842 👈 this PR
5. Add dd-openfeature SDK OpenFeature provider #12843
6. Connect the dd-openfeature SDK to the agent #12844
7. Add agentless and standalone OpenFeature smoke tests #12846

Jira ticket: APMLP-1512

🤖 Generated with Claude Code

[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	14.00 s	13.96 s	[-0.6%; +1.1%] (no difference)
startup:insecure-bank:tracing:Agent	12.93 s	12.99 s	[-1.3%; +0.4%] (no difference)
startup:petclinic:appsec:Agent	17.03 s	16.86 s	[+0.2%; +1.8%] (maybe worse)
startup:petclinic:iast:Agent	16.85 s	16.40 s	[-1.4%; +6.8%] (no difference)
startup:petclinic:profiling:Agent	16.15 s	16.71 s	[-7.6%; +0.9%] (no difference)
startup:petclinic:sca:Agent	17.05 s	16.34 s	[+0.0%; +8.7%] (maybe worse)
startup:petclinic:tracing:Agent	16.05 s	15.97 s	[-0.3%; +1.3%] (no difference)

Commit: d943b6b6 · 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.