Expose isFinished() on AgentSpan

[pavlokhrebto]

What Does This Do

Adds a non-breaking default boolean isFinished() to the AgentSpan interface (internal-api), surfacing the finished state that DDSpan already tracks (durationNano != 0) so other modules can query it without reaching into dd-trace-core.

• DDSpan's existing isFinished() overrides the default — no behavior change.
• The TrackingSpanDecorator test wrapper (the only AgentSpan wrapper) delegates to its wrapped span.
• Leaf / synthetic spans (NoopSpan, etc.) keep the false default.
• Adds a DDSpanTest case asserting false before finish / true after, exercised through the AgentSpan interface.

Motivation

The FFE span-enrichment interceptor (#11658) needs to tell a truly-finished local-root span from a still-running one — with long-running traces enabled, a periodic flush emits the still-running root, and the interceptor currently mis-reads "root present in the flushed batch" as "trace finished". It also wants to resolve the root in O(1) instead of scanning the batch. Both need a finished signal on the interface it uses (AgentSpan). DDSpan already has it, but the interface didn't expose it; this closes only that gap. The consumer change (the interceptor rewrite) lands as a separate follow-up on #11658.

Additional Notes

• Non-breaking: it's a default method, so no existing AgentSpan implementer has to change. Making it abstract would break every implementer.
• No behavior change to existing spans — DDSpan already returns this value.
• Deliberately does not touch MutableSpan / dd-trace-api (the FFE interceptor casts to AgentSpan).

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[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	13.97 s	14.03 s	[-1.3%; +0.4%] (no difference)
startup:insecure-bank:tracing:Agent	13.02 s	13.07 s	[-1.0%; +0.4%] (no difference)
startup:petclinic:appsec:Agent	16.85 s	16.73 s	[-0.3%; +1.8%] (no difference)
startup:petclinic:iast:Agent	16.45 s	16.96 s	[-7.4%; +1.3%] (no difference)
startup:petclinic:profiling:Agent	16.67 s	16.57 s	[-0.5%; +1.8%] (no difference)
startup:petclinic:sca:Agent	16.90 s	16.82 s	[-0.5%; +1.5%] (no difference)
startup:petclinic:tracing:Agent	16.15 s	16.14 s	[-0.8%; +0.9%] (no difference)

Commit: abd6fab3 · CI Pipeline · Benchmarking Platform UI

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[Copilot]

Pull request overview

Adds a non-breaking isFinished() default method to the AgentSpan interface so modules depending on internal-api can query span completion without reaching into dd-trace-core, while preserving existing behavior for DDSpan.

Changes:

• Introduces default boolean isFinished() on AgentSpan (default false).
• Adds a DDSpanTest case asserting isFinished() transitions from false to true after finish(), via the AgentSpan interface.
• Updates TrackingSpanDecorator (test wrapper) to delegate isFinished() to the wrapped span.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
internal-api/src/main/java/datadog/trace/bootstrap/instrumentation/api/AgentSpan.java	Adds isFinished() as a default method on the core span interface.
dd-trace-core/src/test/java/datadog/trace/core/DDSpanTest.java	Adds coverage to validate AgentSpan.isFinished() reflects DDSpan completion.
dd-java-agent/instrumentation-testing/src/main/groovy/datadog/trace/agent/test/TrackingSpanDecorator.groovy	Delegates isFinished() in the AgentSpan test wrapper.

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[datadog-datadog-prod-us1]

🎯 Code Coverage (details)
• Patch Coverage: 0.00%
• Overall Coverage: 56.92% (-0.02%)

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: abd6fab | Docs | Datadog PR Page | Give us feedback!}

[AlexeyKuznetsov-DD]

LGTM.
It would probably be worth getting one more approval from an experienced reviewer before merging.