chore(config): migrate trace sampler to typed configuration

[webern]

Human Summary

This is a relatively straightforward conversion of TraceSamplerConfiguration to typed config. No issues were encountered. The Codex flag is because we are changing our default to match the Agent (which is what we want).

AI Summary

Migrate the trace sampler transform to the typed traces configuration domain.

• Construct TraceSamplerConfiguration from domains.traces instead of GenericConfiguration and ApmConfig.
• Preserve the Saluki-only defaults for the trace sampler in the typed model.
• Remove sampler-only fields, accessors, and legacy deserialization tests from ApmConfig.
• Update the traces pipeline construction to use the typed configuration.

Change Type

• Non-functional (chore, refactoring, docs)

How did you test this PR?

• make fmt
• make build-schema-overlay (no generated drift)
• cargo check --workspace --tests
• cargo clippy -p saluki-components -p agent-data-plane-config-system -p agent-data-plane -p agent-data-plane-config --all-targets
• cargo nextest run -p saluki-components -p agent-data-plane-config-system -p agent-data-plane-config (843 passed, 1 skipped)

References

• Progresses: Migrate saluki codebase to typed configuration. #2169
• Progresses: Migrate APM traces to typed configuration. #2193
• Progresses: Prevent default config drift between ADP and Core Agent #1802

[webern]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• chore(config): migrate trace sampler to typed configuration #2191 👈 (View in Graphite)
• chore(config): migrate datadog trace encoder to typed configuration #2187
• main

This stack of pull requests is managed by Graphite. Learn more about stacking.

[datadog-prod-us1-3]

More details

The migration preserves trace sampler behavior through the resolved configuration path: generated schema defaults still provide the historical 10 TPS values, while Saluki-only defaults and explicit nested settings are seeded into the traces domain. No diff-only behavioral regression was identified. No additional tests recommended: the existing configuration transport coverage already exercises the migrated Saluki-only fields, and execution was blocked by unavailable Rust dependencies.

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Restore the omitted probabilistic sampler percentage fallback

When apm_config.probabilistic_sampler.enabled is set but sampling_percentage is omitted, this now copies the typed Datadog default of 0_f64 from lib/datadog-agent/config/src/generated/datadog_configuration.rs:1769; the removed raw ApmConfig default was 100%, so line 111 builds a sampling rate of 0.0 and the probabilistic path drops all non-error/non-rare traces. Preserve the previous 100% fallback for the omitted-percentage case so this typed-config cutover remains behaviorally transparent.

Useful? React with 👍 / 👎.

[webern]

This is correct and a bugfix that goes toward #1802. ADP should honor the core Agent defaults. Fortunately this feature isn't released to customers yet so only our tests are affected.

[pr-commenter]

Binary Size Analysis (Agent Data Plane)

Baseline: 0f99ce3 · Comparison: fa6af8d · diff
Analysis Configuration: stripped binaries · Pass/Fail Threshold: +5%
Sizes: 40.79 MiB (baseline) vs 41.03 MiB (comparison)
Size Change: +246.12 KiB (+0.59%)

✅ Binary size difference within threshold

Changes by Module

Module	File Size	Symbols
figment	+194.17 KiB	277
saluki_components::common::datadog	-79.81 KiB	109
tonic_prost	+67.70 KiB	23
agent_data_plane_config_system::saluki_env_overlay::PathRecorder	-67.26 KiB	24
otlp_protos::otlp_include::opentelemetry	-49.26 KiB	85
hyper	+43.88 KiB	84
agent_data_plane_config_system::saluki_only::_	+40.65 KiB	9
core	+38.01 KiB	2727
tokio	+37.97 KiB	929
prost	-31.72 KiB	123
h2	-24.09 KiB	138
serde	+24.08 KiB	47
serde_with	+20.49 KiB	15
saluki_components::transforms::dogstatsd_mapper	-17.96 KiB	8
anon.2106486f8d317d0f26c228a10a0c25ea.531.llvm.15798623470946910919	+17.01 KiB	1
anon.4f47395eaac7e6a86c9111625e37e6d6.395.llvm.1637700629175368008	-16.91 KiB	1
hyper_util	-16.42 KiB	10
hashbrown	+14.73 KiB	97
piecemeal	-14.69 KiB	20
saluki_components::encoders::datadog	-14.44 KiB	100

Detailed Symbol Changes

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +2.3%  +266Ki  +2.2%  +200Ki    [13972 Others]
  [NEW] +44.2Ki  [NEW] +43.9Ki    _<agent_data_plane_config_system::saluki_only::_::<impl serde_core::de::Deserialize for agent_data_plane_config_system::saluki_only::SalukiOnly>::deserialize::__Visitor as serde_core::de::Visitor>::visit_map::h029b6a2668b5ce6e
  [NEW] +18.9Ki  [NEW] +18.7Ki    _<tonic_prost::codec::ProstEncoder<T> as tonic::codec::Encoder>::encode::hf2f024643e98714e
  [NEW] +17.0Ki  [NEW]     +76    anon.2106486f8d317d0f26c228a10a0c25ea.531.llvm.15798623470946910919
  [NEW] +12.7Ki  [NEW] +12.6Ki    _<figment::value::de::ConfiguredValueDe<I> as serde_core::de::Deserializer>::deserialize_any::h5b0bc0cf25ffe876
  [NEW] +12.4Ki  [NEW]     +81    anon.2106486f8d317d0f26c228a10a0c25ea.567.llvm.15798623470946910919
  [NEW] +11.6Ki  [NEW] +11.5Ki    _<agent_data_plane_config_system::saluki_env_overlay::StructWalker as serde_core::de::MapAccess>::next_value_seed::hc68cc5819be30644
 +17e2% +11.3Ki +20e2% +11.3Ki    prost::message::Message::encode_to_vec::hec9d535755282a1d
 +48e2% +11.0Ki +81e2% +11.0Ki    std::sys::backtrace::__rust_begin_short_backtrace::h636265569ecef8fc
  [NEW] +10.8Ki  [NEW] +10.7Ki    figment::figment::Figment::extract::haee1684d6196b8e4
  [DEL] -10.9Ki  [DEL] -10.7Ki    saluki_components::sources::otlp::logs::transform::transform_log_record::h3302f377f7bd27f4
  [DEL] -11.5Ki  [DEL] -11.4Ki    h2::server::Connection<T,B>::poll_closed::h92b70f56726577b1
  [DEL] -11.6Ki  [DEL] -11.6Ki    h2::server::Connection<T,B>::poll_closed::hc9c179a40ea7c55d
  [DEL] -12.1Ki  [DEL] -12.0Ki    saluki_components::sources::dogstatsd::replay::writer::run_capture_loop::he083f64fbd1fc69a
  [DEL] -12.2Ki  [DEL]     -81    anon.4f47395eaac7e6a86c9111625e37e6d6.672.llvm.1637700629175368008
  [DEL] -12.4Ki  [DEL] -12.3Ki    h2::server::Connection<T,B>::poll_closed::h29dd8a9319b0a688
  [DEL] -14.2Ki  [DEL] -14.0Ki    saluki_components::common::datadog::apm::_::_<impl serde_core::de::Deserialize for saluki_components::common::datadog::apm::ApmConfiguration>::deserialize::h8279d5536d30f1e2
  [DEL] -15.6Ki  [DEL] -15.3Ki    saluki_components::common::datadog::config::_::_<impl serde_core::de::Deserialize for saluki_components::common::datadog::config::ForwarderConfiguration>::deserialize::h8491640142ecc530
  [DEL] -16.8Ki  [DEL] -16.6Ki    _<agent_data_plane_config_system::saluki_env_overlay::PathRecorder as serde_core::de::Deserializer>::deserialize_struct::h3faf0c90a7e1b643
  [DEL] -16.9Ki  [DEL]     -76    anon.4f47395eaac7e6a86c9111625e37e6d6.395.llvm.1637700629175368008
  [DEL] -36.2Ki  [DEL] -35.9Ki    _<saluki_components::common::datadog::obfuscation::_::<impl serde_core::de::Deserialize for saluki_components::common::datadog::obfuscation::ObfuscationConfig>::deserialize::__Visitor as serde_core::de::Visitor>::visit_map::h04547875805b5e90
  +0.6%  +246Ki  +0.5%  +179Ki    TOTAL

[pr-commenter]

Regression Detector (Agent Data Plane)

Run ID: 0622e0ce-2477-4124-abd8-caa09b1c3ca3
Baseline: 0f99ce37 · Comparison: fa6af8d3 · diff

Optimization Goals: ✅ No significant changes detected

Fine details of change detection per experiment (3)

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
quality_gates_rss_idle	memory	⚪ +0.30	metrics profiles logs
quality_gates_rss_dsd_medium	memory	⚪ +0.24	metrics profiles logs
quality_gates_rss_dsd_low	memory	⚪ -0.24	metrics profiles logs

Bounds Checks: ✅ Passed (3)

experiment	check	replicates	observed	links
quality_gates_rss_dsd_low	memory_usage	10/10	✅ 45.2 MiB ≤ 50 MiB	metrics profiles logs
quality_gates_rss_dsd_medium	memory_usage	10/10	✅ 67 MiB ≤ 75 MiB	metrics profiles logs
quality_gates_rss_idle	memory_usage	10/10	✅ 31.2 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.