chore(config): model duration defaults as a typed value

[jszwedko]

Summary

Follow-up to #1958 (now merged), taking the alternative design proposed in review (#1958 (comment)): model format: duration as a first-class type and store parsed duration defaults in the generated classifier data, instead of carrying an is_duration side channel and reparsing a schema string on every classification. The base type is modeled correctly, and an invalid duration default now breaks the build rather than misbehaving at runtime.

Key changes:

• New go-duration leaf crate owns Go time.ParseDuration parsing. saluki-config's DurationString delegates to it, and the classifier build script uses it too — so the algorithm has a single owner instead of being reimplemented (the parser fix(config): recognize duration keys at their default in the config classifier #1958 added to the classifier is removed). An upstream crate (for example go-parse-duration) can replace this later after vetting; keeping it in-tree for now avoids taking an unvetted external dependency.
• FieldType::Duration (plus a matching ValueType::Duration for the config-testing smoke tests) replaces the is_duration flag. parse_value_type folds format: duration in and panics on an illogical base type. Smoke tests use a generic "42s" value so future duration keys need no bespoke test_json.
• Typed DefaultValue (Missing / Json(&'static str) / DurationNanos(u64)) replaces Option<&str> + is_duration on ClassifierEntry. Codegen parses duration defaults to nanoseconds via go-duration and fails the build if a format: duration default isn't a valid Go duration. The runtime default check simply switches on the typed default; it never parses a schema default.

Behavior matches #1958 for the tls_handshake_timeout bug (a default-valued duration is recognized as default whether sent as nanoseconds or a Go duration string), but the model is cleaner and the failure mode moves to compile time.

Test plan

• go-duration unit tests (Go-style units, signs/fractions/zero, largest value, invalid/overflow, error messages).
• saluki-config duration tests pass against the delegated parser.
• Classifier unit tests updated for DefaultValue (per-variant is_default_value coverage; duration matched both as nanoseconds and as a Go duration string).
• cargo check --workspace --tests and cargo clippy clean; config-testing smoke tests pass.

🤖 Generated with Claude Code

[pr-commenter]

Binary Size Analysis (Agent Data Plane)

Baseline: 4de556d · Comparison: cbd376b · diff
Analysis Configuration: stripped binaries · Pass/Fail Threshold: +5%
Sizes: 41.63 MiB (baseline) vs 41.63 MiB (comparison)
Size Change: +3.74 KiB (+0.01%)

✅ Binary size difference within threshold

Changes by Module

Module	File Size	Symbols
anon.3c69ceabc60ce31e47fb49ebd37b949d.38.llvm.8520628709667317489	+7.95 KiB	1
anon.5043bac4e9f013c95061f55d54848406.113.llvm.4850616680965394514	-7.94 KiB	1
anon.058104e7c5e17815cc397c51159e7bb6.17.llvm.5917434062816465002	+7.47 KiB	1
anon.eb8a6db73655bdd84768962c5db517d1.6.llvm.980884025277214083	-7.46 KiB	1
anon.264f64749ed47b9540def0041d7d333b.77.llvm.1147429972880098824	+6.63 KiB	1
anon.0dc1de58c4eb14eb4a57fa004575eaa2.84.llvm.8144985070982893752	-6.32 KiB	1
anon.122d08581a1227880b36542f3c021e03.7.llvm.16111821345713007611	+4.16 KiB	1
anon.a8b821c4662cac6111d92383c4c8e97b.40.llvm.975721454091953032	-4.16 KiB	1
[Unmapped]	+4.06 KiB	1
go_duration::parse_duration	+4.06 KiB	1
saluki_config::duration_string::parse_duration	-4.04 KiB	1
anon.f05579d214bd720560ee0207fdeaa44b.110.llvm.10277623636693697842	+3.89 KiB	1
anon.5630fd79b5761ba0fc7e0b37ede0e883.119.llvm.15480722195153566423	-3.88 KiB	1
serde_core	+3.53 KiB	1049
crossbeam_channel	-3.53 KiB	160
anon.197e39290976d77f6c512e0753380664.297.llvm.15470508063503015492	-3.37 KiB	1
anon.60bec9cfa65cbbc713774540ce9fa13a.297.llvm.5315471928682786756	+3.37 KiB	1
anon.c2ceec372c14f40e2ac6ec6badd818f6.5.llvm.15452598339203213699	+3.05 KiB	1
anon.3de8e9c07c905cbdb0efe6bb8c0c345e.0.llvm.1672929009223888530	-3.04 KiB	1
anon.12be1b11b7a076fc406c0946a6016761.359.llvm.12380805039573619983	+2.84 KiB	1

Detailed Symbol Changes

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  [NEW] +56.8Ki  [NEW] +56.6Ki    saluki_components::common::datadog::io::run_endpoint_io_loop::_{{closure}}::h54fbb73bb30184e6
  [NEW] +44.7Ki  [NEW] +44.6Ki    agent_data_plane::cli::run::handle_run_command::_{{closure}}::h83501a7881036c5f
  [NEW] +38.7Ki  [NEW] +38.5Ki    _<saluki_components::forwarders::otlp::OtlpForwarder as saluki_core::components::forwarders::Forwarder>::run::_{{closure}}::h3cd6ee67f0471508
  [NEW] +32.6Ki  [NEW] +32.4Ki    _<saluki_components::transforms::aggregate::Aggregate as saluki_core::components::transforms::Transform>::run::_{{closure}}::h72e4b09fd816d94f
  [NEW] +28.6Ki  [NEW] +28.5Ki    agent_data_plane::cli::dogstatsd::handle_dogstatsd_command::_{{closure}}::h84db3f7ad161eab2
  [NEW] +28.6Ki  [NEW] +28.5Ki    saluki_components::sources::otlp::metrics::translator::OtlpMetricsTranslator::translate_metrics::h1e8351a6f731e9df
  [NEW] +27.2Ki  [NEW] +26.9Ki    _<saluki_components::sources::dogstatsd::_::<impl serde_core::de::Deserialize for saluki_components::sources::dogstatsd::DogStatsDConfiguration>::deserialize::__Visitor as serde_core::de::Visitor>::visit_map::hfc578ba92a99992a
  [NEW] +26.6Ki  [NEW] +26.4Ki    _<saluki_components::sources::dogstatsd::DogStatsDConfiguration as saluki_core::components::sources::builder::SourceBuilder>::build::_{{closure}}::h2c2a33d551977c6d
  [NEW] +25.6Ki  [NEW] +25.4Ki    saluki_components::sources::dogstatsd::drive_stream::_{{closure}}::h3fe2520e3abdfc38
  [NEW] +25.0Ki  [NEW] +24.8Ki    agent_data_plane::internal::remote_agent::run_remote_agent_registration_loop::_{{closure}}::h64859e60eb17f920
  +0.0% +3.45Ki  -0.0%    -354    [44936 Others]
  [DEL] -25.0Ki  [DEL] -24.8Ki    agent_data_plane::internal::remote_agent::run_remote_agent_registration_loop::_{{closure}}::h4e2e551f8139db38
  [DEL] -25.6Ki  [DEL] -25.5Ki    saluki_components::sources::dogstatsd::drive_stream::_{{closure}}::hc4388ae93a328f58
  [DEL] -26.5Ki  [DEL] -26.3Ki    _<saluki_components::sources::dogstatsd::DogStatsDConfiguration as saluki_core::components::sources::builder::SourceBuilder>::build::_{{closure}}::h9b7f1b7f5ed53de7
  [DEL] -27.2Ki  [DEL] -26.9Ki    _<saluki_components::sources::dogstatsd::_::<impl serde_core::de::Deserialize for saluki_components::sources::dogstatsd::DogStatsDConfiguration>::deserialize::__Visitor as serde_core::de::Visitor>::visit_map::hf9734c02c96e53ea
  [DEL] -28.6Ki  [DEL] -28.4Ki    saluki_components::sources::otlp::metrics::translator::OtlpMetricsTranslator::translate_metrics::h762652f9497ab51c
  [DEL] -28.6Ki  [DEL] -28.5Ki    agent_data_plane::cli::dogstatsd::handle_dogstatsd_command::_{{closure}}::h20260c826fa2e80d
  [DEL] -32.5Ki  [DEL] -32.3Ki    _<saluki_components::transforms::aggregate::Aggregate as saluki_core::components::transforms::Transform>::run::_{{closure}}::h5255c5fdf9a6142d
  [DEL] -38.7Ki  [DEL] -38.5Ki    _<saluki_components::forwarders::otlp::OtlpForwarder as saluki_core::components::forwarders::Forwarder>::run::_{{closure}}::hf061731a7e18b6ce
  [DEL] -44.7Ki  [DEL] -44.6Ki    agent_data_plane::cli::run::handle_run_command::_{{closure}}::hc38d95056d131633
  [DEL] -56.6Ki  [DEL] -56.4Ki    saluki_components::common::datadog::io::run_endpoint_io_loop::_{{closure}}::h576e42a88b0e33a6
  +0.0% +3.74Ki  -0.0%     -60    TOTAL

[pr-commenter]

Regression Detector (Agent Data Plane)

Run ID: ea0a57da-336a-4219-b958-ff1b83710556
Baseline: 4de556d0 · Comparison: cbd376be · diff

Optimization Goals: ✅ No significant changes detected

Fine details of change detection per experiment (5)

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_dsd_medium	memory	⚪ +0.03	metrics profiles logs
quality_gates_rss_idle	memory	⚪ +0.01	metrics profiles logs
quality_gates_rss_dsd_ultraheavy	memory	⚪ -0.03	metrics profiles logs
quality_gates_rss_dsd_heavy	memory	⚪ -0.06	metrics profiles logs
quality_gates_rss_dsd_low	memory	⚪ -0.11	metrics profiles logs

Bounds Checks: ✅ Passed (5)

experiment	check	replicates	observed	links
quality_gates_rss_dsd_heavy	memory_usage	10/10	✅ 131 MiB ≤ 140 MiB	metrics profiles logs
quality_gates_rss_dsd_low	memory_usage	10/10	✅ 42.9 MiB ≤ 50 MiB	metrics profiles logs
quality_gates_rss_dsd_medium	memory_usage	10/10	✅ 64.8 MiB ≤ 75 MiB	metrics profiles logs
quality_gates_rss_dsd_ultraheavy	memory_usage	10/10	✅ 191 MiB ≤ 200 MiB	metrics profiles logs
quality_gates_rss_idle	memory_usage	10/10	✅ 29 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.

[webern]

LGTM on a quick pass and does what I think I need on my branch(es) 👍