Add decoded span assert rules

[PerfectSlayer]

What Does This Do

This PR introduces decoded span assert rules.

EDIT: This PR unit tests need test agent JSON  span deserialization first. I’ll introduce an intermediate PR to the stack to add it. It is still good to review in the meantime.

Motivation

The goal is to provide capabilities for smoke tests to evaluate trace and span structures and values.

Additional Notes

This is mainly inspired from my prior work with instrumentation tests but decoded spans are not like DDSpan. They don’t hold the same values / types so new rules needed to be put in place for smoke tests.

Contributor Checklist

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Jira ticket: APMLP-1247

[datadog-datadog-prod-us1-2]

Bits has a CI fix ready

🟢 Investigated · 🟢 Fix prepared · ⚪ Validation skipped · 🟠 Ready

SmokeMatcherTest imports the nonexistent datadog.smoketest.backend.TestAgentTraceDecoder, so the smoke-test compile job cannot resolve its synthetic trace fixtures. The tests now create lightweight in-test DecodedTrace and DecodedSpan fixtures, preserving the matcher coverage without depending on an unavailable backend decoder.

Commit fix to this PR

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View in Datadog | Reviewed commit 5134699 · Any feedback? Reach out in #deveng-pr-agent

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[datadog-datadog-prod-us1-2]

🎯 Code Coverage (details)
• Patch Coverage: 2.44%
• Overall Coverage: 57.51% (-0.03%)

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🔗 Commit SHA: 798798a | Docs | Datadog PR Page | Give us feedback!}

[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	13.96 s	13.85 s	[+0.0%; +1.6%] (maybe worse)
startup:insecure-bank:tracing:Agent	12.95 s	13.00 s	[-0.9%; +0.1%] (no difference)
startup:petclinic:appsec:Agent	17.03 s	16.77 s	[+0.7%; +2.4%] (maybe worse)
startup:petclinic:iast:Agent	17.02 s	17.04 s	[-1.0%; +0.7%] (no difference)
startup:petclinic:profiling:Agent	16.70 s	16.80 s	[-1.5%; +0.2%] (no difference)
startup:petclinic:sca:Agent	16.94 s	16.98 s	[-1.1%; +0.6%] (no difference)
startup:petclinic:tracing:Agent	16.16 s	16.10 s	[-0.6%; +1.3%] (no difference)

Commit: 798798ab · 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.

[PerfectSlayer]

@autotest review

[datadog-datadog-prod-us1-2]

Unordered trace matching can reject a valid trace when a reusable childOfPrevious matcher first probes a non-matching candidate: assertSpan mutates the matcher to that candidate's parent ID, so later candidates are checked against stale state. Keep the resolved parent matcher local instead of mutating the configured matcher.

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[datadog-datadog-prod-us1-2]

More details

The decoder and assertion paths do not show a confirmed behavioral regression or diff-only production hazard. Adversarial cases were reviewed for malformed JSON, unsigned IDs, missing fields, duplicate/unordered trace matching, ancestry ordering, partial trace chunks, and nested meta_struct values; execution was blocked before tests ran because the checkout requires JDK 25 and the sandbox has only JDK 8/11/17/21.

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