Carry the agent manifest inside metadata so it reaches the backend

[ncybul]

What Does This Do

annotateAgentManifest() (shipped in v1.66.0) wrote the manifest to meta.agent_manifest, but the backend reads it from meta.metadata._dd.agent_manifest, so Java manifests never showed up in agent tracking.

The manifest now goes into the existing metadata span tag under the reserved _dd namespace, so it serializes to the right place. Since it is no longer a span tag of its own, LLMObsSpanMapper loses its dedicated branch and wire key.

The public API is unchanged — no caller changes needed.

Manual Testing

Verified that agent manifest annotation gets stored on the span correctly (trace)

Contributor Checklist

• Format code with ./gradlew spotlessApply
• :dd-trace-core:test and :dd-java-agent:agent-llmobs:test pass locally
• Existing manifest tests updated to the new location

Claude session: 1d00ff6a-4bf0-49b6-94c5-3464fb28b08f
Resume: claude --resume 1d00ff6a-4bf0-49b6-94c5-3464fb28b08f

🤖 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	14.07 s	14.01 s	[-0.4%; +1.3%] (no difference)
startup:insecure-bank:tracing:Agent	12.97 s	13.09 s	[-1.7%; -0.2%] (maybe better)
startup:petclinic:appsec:Agent	17.01 s	16.85 s	[+0.1%; +1.8%] (maybe worse)
startup:petclinic:iast:Agent	16.90 s	17.00 s	[-1.5%; +0.3%] (no difference)
startup:petclinic:profiling:Agent	16.62 s	16.94 s	[-3.1%; -0.7%] (maybe better)
startup:petclinic:sca:Agent	16.86 s	16.24 s	[-0.5%; +8.1%] (no difference)
startup:petclinic:tracing:Agent	16.01 s	16.06 s	[-1.4%; +0.8%] (no difference)

Commit: a0f917b0 · CI Pipeline · Benchmarking Platform UI

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

[datadog-prod-us1-6]

More details

The mapper keeps the agent manifest at meta.metadata._dd.agent_manifest. The updated tests cover storage and serialization at this path.

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[yahya-mouman]

Is it possible to read it from both spots in the backend to not lose on data coming from this update ?

[ncybul]

Is it possible to read it from both spots in the backend to not lose on data coming from this update ?

@yahya-mouman I would probably suggest against that just because we don't want to add more tech debt to our backend for an update that we have yet to document. It's probably better to patch 1.66 release line instead.

[ncybul]

/merge

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2026-09-18 13:38:10 UTC ℹ️ Start processing command /merge

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2026-09-18 13:38:21 UTC ℹ️ MergeQueue: Pull request is not mergeable yet

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2026-09-18 14:57:23 UTC ℹ️ MergeQueue: merge request added to the queue

The expected merge time in master is approximately 1h (p90).

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2026-09-18 16:02:07 UTC ℹ️ MergeQueue: This merge request was merged

[ncybul]

/merge

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2026-09-18 14:10:29 UTC ℹ️ Start processing command /merge

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2026-09-18 14:10:32 UTC ❌ MergeQueue

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