enhancement(core): unify trace event model with Datadog Agent

[ajgajg1134]

Summary

• Replaces three separate span tag maps (meta/metrics/meta_struct) and the scalar-only AttributeScalarValue with a single AttributeValue enum covering all typed variants (String, Bool, Int, Float, Bytes, Array, KeyValueList)
• Introduces PayloadFields struct on Trace that promotes tracer-payload metadata (container ID, language, version, env, hostname, runtime ID) from wire-format to first-class fields
• Flattens TraceSampling into direct fields on Trace (priority, dropped_trace, sampling_mechanism, decision_maker, otlp_sampling_rate)
• Moves Span.trace_id to Trace.trace_id_low / Trace.trace_id_high for 128-bit trace ID support
• Widens SpanLink.attributes from FastHashMap<MetaString, MetaString> to FastHashMap<MetaString, AttributeValue>

All existing callers in the OTLP pipeline are updated to the new API: OTLP translator, APM stats transform (concentrator, aggregation, weight), trace obfuscation, trace sampler (all sub-modules), and the existing OTLP encoder.

Builder methods with_meta, with_metrics, with_meta_struct are preserved on Span as migration helpers that insert into the unified attributes map, keeping callers on the feature branch working with no changes needed for this PR.

Test plan

• cargo test -p saluki-core -p saluki-components passes (548 tests)
• Review data model changes in lib/saluki-core/src/data_model/event/trace/mod.rs
• Review OTLP translator alignment with receiveResourceSpansV2 in the Go agent

Mostly generated with Claude Code but also with Andrew 😎

[pr-commenter]

Binary Size Analysis (Agent Data Plane)

Baseline: 66002de · Comparison: e6a8467 · diff
Analysis Configuration: stripped binaries · Pass/Fail Threshold: +5%
Sizes: 37.32 MiB (baseline) vs 37.34 MiB (comparison)
Size Change: +22.20 KiB (+0.06%)

✅ Binary size difference within threshold

Changes by Module

Module	File Size	Symbols
figment	+122.17 KiB	224
hyper_util	-32.35 KiB	59
prost	-31.52 KiB	160
anyhow	-30.97 KiB	406
alloc	+24.08 KiB	786
saluki_components::common::datadog	-21.51 KiB	89
piecemeal	+18.71 KiB	22
tonic	-16.78 KiB	221
serde_core	+13.45 KiB	121
h2	+11.94 KiB	206
saluki_components::transforms::dogstatsd_mapper	-11.89 KiB	7
serde_with	+11.89 KiB	33
hyper	+9.48 KiB	204
axum	+9.07 KiB	172
core	-8.89 KiB	2173
hashbrown	-8.59 KiB	225
datadog_protos::trace_piecemeal_include::datadog	-8.36 KiB	20
[sections]	+7.55 KiB	8
crossbeam_channel	+7.21 KiB	35
std	-6.25 KiB	148

Detailed Symbol Changes

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  [NEW] +43.0Ki  [NEW] +42.9Ki    saluki_components::transforms::apm_stats::ApmStats::process_trace::h9f9ed1c4c23abc68
  +0.2% +29.7Ki  +0.2% +20.0Ki    [12931 Others]
  [NEW] +25.2Ki  [NEW] +25.1Ki    saluki_components::common::otlp::traces::transform::otel_to_dd_span_minimal::h04cf0c23de922836
  [NEW] +21.3Ki  [NEW] +21.2Ki    _<figment::value::de::ConfiguredValueDe<I> as serde_core::de::Deserializer>::deserialize_struct::hed9234a71ae20cd4
  [NEW] +19.9Ki  [NEW] +19.8Ki    saluki_components::common::otlp::traces::transform::otel_span_to_dd_span::h86244c487e8ed2d5
  +101% +19.1Ki  +102% +19.0Ki    agent_data_plane::internal::env::ADPEnvironmentProvider::from_configuration::_{{closure}}::hf4fc2f25aacab3e6
   +97% +18.4Ki   +98% +18.3Ki    agent_data_plane::internal::env::workload::build_collector::_{{closure}}::h28d4115e9cfd8e68
  +297% +17.2Ki  +302% +17.2Ki    h2::proto::connection::DynConnection<B>::recv_frame::h0fe91f2f6ee9ac4a
  [NEW] +14.6Ki  [NEW] +14.5Ki    _<figment::value::de::ConfiguredValueDe<I> as serde_core::de::Deserializer>::deserialize_struct::h6948f527d7ba396f
  [NEW] +12.9Ki  [NEW] +12.7Ki    _<figment::value::magic::RelativePathBuf as figment::value::magic::Magic>::deserialize_from::hbaa30d53055c9377
 +52e2% +12.5Ki +31e3% +12.5Ki    _<saluki_components::transforms::trace_sampler::TraceSampler as saluki_core::components::transforms::SynchronousTransform>::transform_buffer::hf35cdf66ba7a245f
  [DEL] -14.2Ki  [DEL] -14.0Ki    saluki_components::common::datadog::apm::_::_<impl serde_core::de::Deserialize for saluki_components::common::datadog::apm::ApmConfiguration>::deserialize::haaad9ebeb9100870
  [DEL] -15.3Ki  [DEL] -15.2Ki    h2::server::Connection<T,B>::poll_closed::h2d88ac9d7f1e941c
  [DEL] -15.4Ki  [DEL] -15.3Ki    h2::server::Connection<T,B>::poll_closed::h83203de9713e50cd
  [DEL] -16.9Ki  [DEL] -16.8Ki    h2::server::Connection<T,B>::poll_closed::h5b7f429aa9aaf99d
  [DEL] -18.9Ki  [DEL] -18.8Ki    _<hyper_util::server::conn::auto::Connection<I,S,E> as core::future::future::Future>::poll::h2d49a88a91640cc8
  [DEL] -21.8Ki  [DEL] -21.6Ki    saluki_components::common::otlp::traces::transform::otel_span_to_dd_span::h12a6ada56460ed27
 -61.6% -22.8Ki -61.8% -22.8Ki    saluki_components::sources::otlp::metrics::translator::OtlpMetricsTranslator::translate_metrics::ha7c3f501c30996a6
  [DEL] -25.6Ki  [DEL] -25.5Ki    saluki_components::common::otlp::traces::transform::otel_to_dd_span_minimal::h32cc9c15b28458d7
 -49.1% -29.5Ki -49.2% -29.5Ki    agent_data_plane::internal::env::workload::RemoteAgentWorkloadProvider::from_configuration::_{{closure}}::hea9789cc98b277de
  [DEL] -31.3Ki  [DEL] -31.2Ki    saluki_components::transforms::apm_stats::ApmStats::process_trace::h4fce2ef29c70bbcd
  +0.1% +22.2Ki  +0.0% +12.7Ki    TOTAL

[pr-commenter]

Regression Detector (Agent Data Plane)

Run ID: e00c5dc8-085c-48bb-97bb-8dea3a60e81e
Baseline: 66002dee · Comparison: e6a8467e · diff

Optimization Goals: ✅ No significant changes detected

Fine details of change detection per experiment (35)

Experiments configured erratic: true are tagged (ignored) and skipped when determining which experiments regressed or improved. Experiments which are detected as erratic at runtime are tagged (erratic) to flag that the run's sample dispersion was high, but their regression / improvement signal still counts.

experiment	goal	Δ mean %	links
dsd_uds_512kb_3k_contexts_cpu (erratic)	cpu	⚪ +5.88	metrics profiles logs
otlp_ingest_traces_ottl_transform_5mb_memory	memory	⚪ +4.32	metrics profiles logs
dsd_uds_1mb_3k_contexts_cpu (erratic)	cpu	⚪ +4.21	metrics profiles logs
otlp_ingest_traces_5mb_memory	memory	⚪ +4.12	metrics profiles logs
otlp_ingest_metrics_5mb_cpu (erratic)	cpu	⚪ +3.80	metrics profiles logs
otlp_ingest_traces_ottl_filtering_5mb_memory	memory	⚪ +3.19	metrics profiles logs
otlp_ingest_logs_5mb_cpu (ignored)	cpu	⚪ +3.16	metrics profiles logs
dsd_uds_100mb_3k_contexts_cpu (erratic)	cpu	⚪ +3.08	metrics profiles logs
dsd_uds_500mb_3k_contexts_throughput	throughput	⚪ -2.55	metrics profiles logs
dsd_uds_10mb_3k_contexts_cpu (erratic)	cpu	⚪ +2.54	metrics profiles logs
otlp_ingest_logs_5mb_memory (ignored)	memory	⚪ +2.35	metrics profiles logs
otlp_ingest_traces_ottl_filtering_5mb_cpu (erratic)	cpu	⚪ +1.79	metrics profiles logs
otlp_ingest_traces_ottl_transform_5mb_cpu (erratic)	cpu	⚪ +1.47	metrics profiles logs
quality_gates_rss_dsd_ultraheavy	memory	⚪ +0.49	metrics profiles logs
dsd_uds_1mb_3k_contexts_memory	memory	⚪ +0.40	metrics profiles logs
quality_gates_rss_dsd_low	memory	⚪ +0.36	metrics profiles logs
quality_gates_rss_dsd_heavy	memory	⚪ +0.25	metrics profiles logs
otlp_ingest_traces_ottl_filtering_5mb_throughput	throughput	⚪ -0.16	metrics profiles logs
dsd_uds_100mb_3k_contexts_memory	memory	⚪ +0.15	metrics profiles logs
otlp_ingest_traces_5mb_throughput	throughput	⚪ -0.07	metrics profiles logs
dsd_uds_10mb_3k_contexts_throughput	throughput	⚪ -0.01	metrics profiles logs
dsd_uds_512kb_3k_contexts_throughput	throughput	⚪ +0.00	metrics profiles logs
dsd_uds_1mb_3k_contexts_throughput	throughput	⚪ +0.00	metrics profiles logs
dsd_uds_512kb_3k_contexts_memory	memory	⚪ -0.00	metrics profiles logs
otlp_ingest_traces_ottl_transform_5mb_throughput	throughput	⚪ +0.01	metrics profiles logs
dsd_uds_500mb_3k_contexts_memory	memory	⚪ -0.02	metrics profiles logs
dsd_uds_100mb_3k_contexts_throughput	throughput	⚪ +0.02	metrics profiles logs
otlp_ingest_metrics_5mb_throughput	throughput	⚪ +0.03	metrics profiles logs
otlp_ingest_logs_5mb_throughput (ignored)	throughput	⚪ +0.03	metrics profiles logs
dsd_uds_500mb_3k_contexts_cpu (erratic)	cpu	⚪ -0.15	metrics profiles logs
otlp_ingest_traces_5mb_cpu (erratic)	cpu	⚪ -0.21	metrics profiles logs
dsd_uds_10mb_3k_contexts_memory	memory	⚪ -0.27	metrics profiles logs
quality_gates_rss_dsd_medium	memory	⚪ -0.34	metrics profiles logs
quality_gates_rss_idle	memory	⚪ -1.43	metrics profiles logs
otlp_ingest_metrics_5mb_memory	memory	⚪ -3.45	metrics profiles logs

Bounds Checks: ✅ Passed (5)

experiment	check	replicates	observed	links
quality_gates_rss_dsd_heavy	memory_usage	10/10	✅ 126 MiB ≤ 140 MiB	metrics profiles logs
quality_gates_rss_dsd_low	memory_usage	10/10	✅ 39 MiB ≤ 50 MiB	metrics profiles logs
quality_gates_rss_dsd_medium	memory_usage	10/10	✅ 60.6 MiB ≤ 75 MiB	metrics profiles logs
quality_gates_rss_dsd_ultraheavy	memory_usage	10/10	✅ 183 MiB ≤ 200 MiB	metrics profiles logs
quality_gates_rss_idle	memory_usage	10/10	✅ 26.6 MiB ≤ 40 MiB	metrics profiles logs

Explanation

A change is flagged as a regression when |Δ mean %| > 5.00% in the regressing direction for its optimization goal AND SMP marks the experiment as a regression (is_regression: true). Improvements use the matching criteria for the improving direction. Experiments configured erratic: true (tagged (ignored)) are skipped outright; experiments detected as erratic at runtime (tagged (erratic)) still count, since that flag describes sample dispersion rather than directional certainty. The Δ mean % cell is colored accordingly: 🟢 = improvement, 🔴 = regression, ⚪ = neutral. Reduction in CPU or memory is an improvement; reduction in ingress throughput is a regression.