chore(config): add runtime configuration updates

[webern]

Human Summary

Adds a typed configuration update subscription mechanism, known as Live<T>.

The contract is to get a Live from the type system like this:

let live = config_system.live(|c| &c.domains.dogstatsd.debug_log)

Then you put live.changes() in your tokio select!

  _ = live.changed() => {
      let metrics_stats_enabled = live.current().metrics_stats_enable;
      self.metrics_stats_enabled = metrics_stats_enabled;
      debug!(metrics_stats_enabled, "Updated DogStatsD metrics stats debug logging gate.");

AI Summary

Adds the typed runtime configuration library and Live<T> view without wiring it into the Agent Data Plane binary.

Configuration system

The new agent-data-plane-config-system crate translates two configuration sources into the ADP-native SalukiConfiguration model:

• Datadog configuration, translated through the generated configuration witness
• Saluki-only configuration, which seeds fields not represented in the Datadog schema

ConfigurationSystem:

• translates an initial GenericConfiguration into a complete typed configuration
• subscribes to updates when the source map is dynamic
• coalesces bursts of updates before re-translating
• fails startup when the initial source cannot be translated
• keeps runtime updates durable by retaining defaults for invalid translated values while applying other valid changes
• exposes the current configuration through a shared ArcSwap

Live view of the configuration

Live<T> in agent-data-plane-config provides a typed view over a projection of SalukiConfiguration:

• Live::fixed creates a value that never changes
• Live::dynamic tracks a shared configuration snapshot
• current() returns the latest projected value
• Deref reads the view's latest snapshot
• changed() waits for the projected value to change
• project() narrows a view to a child node or field

The view uses ArcSwap for consistent snapshots and a Tokio watch channel for update notifications. A view only wakes its consumer when its projected value changes.

This PR is library-only. It does not modify bin/agent-data-plane, wire the configuration system into startup, add the /config/internal endpoint, or add integration-test coverage. Those changes are deferred to PR-3b, where environment handling and runtime wiring will be addressed together.

Change Type

• Non-functional (chore, refactoring, docs)

How did you test this PR?

• make check-clippy
• Unit tests in agent-data-plane-config-system cover startup translation, translation errors, update convergence, projections, field-level live views, fixed views, and startup values.

No integration test is included in this PR because the Agent Data Plane wiring is deferred to PR-3b.

References

• Depends on chore(config): typed config foundation #1957

[webern]

• chore(config): cutover adp bin components to typed config system #1995
• chore(config): cutover saluki-components to the new typed configuration system #1987
• chore(config): build the first components from the typed configuration model #1979
• chore(config): fix the struct shape for saluki-only fields #1986
• chore(config): add runtime configuration updates #1977 👈 (View in Graphite)
• chore(config): typed config foundation #1957
• main

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[pr-commenter]

Regression Detector (Agent Data Plane)

Run ID: 98efdb26-3dfb-4d8f-993a-5857785e717e
Baseline: 2715682b · Comparison: 7f68a1a5 · 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_idle	memory	⚪ +0.25	metrics profiles logs
quality_gates_rss_dsd_ultraheavy	memory	⚪ +0.17	metrics profiles logs
quality_gates_rss_dsd_low	memory	⚪ +0.15	metrics profiles logs
quality_gates_rss_dsd_medium	memory	⚪ -0.12	metrics profiles logs
quality_gates_rss_dsd_heavy	memory	⚪ -0.13	metrics profiles logs

Bounds Checks: ✅ Passed (5)

experiment	check	replicates	observed	links
quality_gates_rss_dsd_heavy	memory_usage	10/10	✅ 133 MiB ≤ 140 MiB	metrics profiles logs
quality_gates_rss_dsd_low	memory_usage	10/10	✅ 43.2 MiB ≤ 50 MiB	metrics profiles logs
quality_gates_rss_dsd_medium	memory_usage	10/10	✅ 64.7 MiB ≤ 75 MiB	metrics profiles logs
quality_gates_rss_dsd_ultraheavy	memory_usage	10/10	✅ 192 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.

[pr-commenter]

Binary Size Analysis (Agent Data Plane)

Baseline: 2715682 · Comparison: 7f68a1a · diff
Analysis Configuration: stripped binaries · Pass/Fail Threshold: +5%
Sizes: 41.54 MiB (baseline) vs 41.54 MiB (comparison)
Size Change: +0 B (+0.00%)

✅ Binary size difference within threshold

Changes by Module

Module	File Size	Symbols
anon.104b1f618a14d6d60f2ebe1b651d81f5.1.llvm.4906596154882173116	+129 B	1
anon.104b1f618a14d6d60f2ebe1b651d81f5.1.llvm.1709475780185287723	-129 B	1
anon.104b1f618a14d6d60f2ebe1b651d81f5.4.llvm.4906596154882173116	+114 B	1
anon.104b1f618a14d6d60f2ebe1b651d81f5.4.llvm.1709475780185287723	-114 B	1
anon.104b1f618a14d6d60f2ebe1b651d81f5.3.llvm.4906596154882173116	+108 B	1
anon.104b1f618a14d6d60f2ebe1b651d81f5.3.llvm.1709475780185287723	-108 B	1
anon.104b1f618a14d6d60f2ebe1b651d81f5.0.llvm.4906596154882173116	+96 B	1
anon.104b1f618a14d6d60f2ebe1b651d81f5.0.llvm.1709475780185287723	-96 B	1
anon.104b1f618a14d6d60f2ebe1b651d81f5.2.llvm.4906596154882173116	+94 B	1
anon.104b1f618a14d6d60f2ebe1b651d81f5.2.llvm.1709475780185287723	-94 B	1

Detailed Symbol Changes

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  [NEW]    +129  [NEW]     +40    anon.104b1f618a14d6d60f2ebe1b651d81f5.1.llvm.4906596154882173116
  [NEW]    +114  [NEW]     +25    anon.104b1f618a14d6d60f2ebe1b651d81f5.4.llvm.4906596154882173116
  [NEW]    +108  [NEW]     +19    anon.104b1f618a14d6d60f2ebe1b651d81f5.3.llvm.4906596154882173116
  [NEW]     +96  [NEW]      +7    anon.104b1f618a14d6d60f2ebe1b651d81f5.0.llvm.4906596154882173116
  [NEW]     +94  [NEW]      +5    anon.104b1f618a14d6d60f2ebe1b651d81f5.2.llvm.4906596154882173116
  [DEL]     -94  [DEL]      -5    anon.104b1f618a14d6d60f2ebe1b651d81f5.2.llvm.1709475780185287723
  [DEL]     -96  [DEL]      -7    anon.104b1f618a14d6d60f2ebe1b651d81f5.0.llvm.1709475780185287723
  [DEL]    -108  [DEL]     -19    anon.104b1f618a14d6d60f2ebe1b651d81f5.3.llvm.1709475780185287723
  [DEL]    -114  [DEL]     -25    anon.104b1f618a14d6d60f2ebe1b651d81f5.4.llvm.1709475780185287723
  [DEL]    -129  [DEL]     -40    anon.104b1f618a14d6d60f2ebe1b651d81f5.1.llvm.1709475780185287723
  [ = ]       0  [ = ]       0    TOTAL

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[webern]

I removed the integration with agent-data-plane because it needs more work as @tobz and the bot recognized.

This push removes the agent-data-plane touch points so I can still land the reviewed Live<T> work.

https://github.com/DataDog/saluki/compare/32eb7749c8369b102967c36c78af0ddd8947de69..7f68a1a5eb845da6dfd863aebf740de0b6394df5