Fix app context attributes wiped by ddprof setContext on span activation

[jbachorik]

What Does This Do

Preserves application-managed ddprof context attributes across span activation/deactivation, and restores them via a zero-allocation path using the new setContextValuesByIdAndBytes API (ddprof 1.45.0-SNAPSHOT).

ddprof's setContext wipes all custom attribute slots when a span is activated. This change:

• Snapshots each app-managed attribute per-thread in an AppContextSnapshot (constant ID + pre-encoded UTF-8 bytes) whenever setContextValue/clearContextValue is called
• Skips re-encoding and re-snapshotting when the same value is set again on the same thread (common steady-state: same operation name across consecutive spans)
• Re-applies both the DD sidecar encoding and the OTEP attrs_data value via a single setContextValuesByIdAndBytes call after every setSpanContext — no String allocation, no hash lookup, no OTEP sidecar gap
• Releases the ThreadLocal when all slots are cleared (avoiding memory leak on pooled threads)
• Sizes snapshot arrays to ContextSetter's actual internal size (deduplicated, max 10) rather than the raw attribute list size

Motivation

Application-set profiling context attributes (e.g. custom tags set via ProfilingContextAttribute.set()) were silently dropped on every span activation. This caused flaky profiling tests and incorrect/missing context in profiles when both span context and app context were in use simultaneously.

Additional Notes

• Requires ddprof 1.45.0-SNAPSHOT (setContextValuesByIdAndBytes on ContextSetter / ThreadContext) — tracked in PROF-15098
• ThreadContext.setContextValuesByIdAndBytes validates input before mutating (no half-written records on bad input) and skips slots with constantId <= 0
• hasAppContextAttributes() and the redundant HAS_APP_CONTEXT static guard in DatadogProfilingIntegration were removed — reapplyAppContext() already short-circuits on !hasAppContext
• Constant IDs are stable once registered in the global pool; the per-thread 256-entry ThreadContext cache makes the initial setContextAttribute cheap on repeated values

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Jira ticket: [PROF-15096]

[datadog-prod-us1-4]

✨ Fix all issues with BitsAI

⚠️ Warnings

🚦 9 Pipeline jobs failed

DataDog/apm-reliability/dd-trace-java | build     

DataDog/apm-reliability/dd-trace-java | build_tests: [:baseTest, base]     

DataDog/apm-reliability/dd-trace-java | build_tests: [:instrumentationLatestDepTest, latestdep]     

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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	13.91 s	13.91 s	[-0.8%; +0.8%] (no difference)
startup:insecure-bank:tracing:Agent	12.90 s	12.94 s	[-1.1%; +0.5%] (no difference)
startup:petclinic:appsec:Agent	16.81 s	16.10 s	[+0.0%; +8.9%] (maybe worse)
startup:petclinic:iast:Agent	16.31 s	16.85 s	[-7.4%; +0.9%] (no difference)
startup:petclinic:profiling:Agent	16.76 s	16.79 s	[-1.5%; +1.0%] (no difference)
startup:petclinic:sca:Agent	16.67 s	16.68 s	[-1.0%; +0.8%] (no difference)
startup:petclinic:tracing:Agent	15.93 s	15.98 s	[-1.3%; +0.7%] (no difference)

Commit: 1a2464b7 · CI Pipeline · Benchmarking Platform UI

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