chore(agent-data-plane): share shutdown signal wait logic

[jszwedko]

Human Summary

Refactors the shutdown wait handler into a shared module that can be used where ever we need to wait to ensure we consistently rely on the same signals, cross-platform.

AI Summary

#2322 added SIGTERM/SIGINT handling for graceful shutdown, but the same signal-waiting logic was duplicated between the run command and dogstatsd replay's cancellation setup. An earlier version of this PR tried to close a related gap -- a signal delivered before the supervisor starts falling through to the OS's default disposition -- by registering signal handlers eagerly at process start. Per discussion on #2322, that gap doesn't need graceful handling: an abrupt exit before the supervisor is running is acceptable. This PR instead does a pure refactor, extracting the existing lazy signal-wait logic into a shared saluki_app::util::wait_for_shutdown_signal helper used by both run and dogstatsd replay, removing the duplication and making it reusable by any binary built on the saluki crates, not just agent-data-plane.

Test plan

• cargo check --workspace, cargo clippy -p agent-data-plane -p saluki-app --no-deps pass.
• No new automated tests added; this is a non-behavioral refactor of existing signal-handling code.

[pr-commenter]

Binary Size Analysis (Agent Data Plane)

Baseline: 6825bb3 · Comparison: d601d0f · diff
Analysis Configuration: stripped binaries · Pass/Fail Threshold: +5%
Sizes: 41.65 MiB (baseline) vs 41.53 MiB (comparison)
Size Change: -132.69 KiB (-0.31%)

✅ Binary size difference within threshold

Changes by Module

Module	File Size	Symbols
core	-53.34 KiB	1663
[sections]	-20.04 KiB	7
anon.091bbad26cc3924e9c77bf8d4e018d37.460.llvm.16286174339815826116	-17.53 KiB	1
anon.24f983bdb5d7a9f41626c5544756a394.887.llvm.10441113739384331192	+17.52 KiB	1
tokio	-14.51 KiB	916
agent_data_plane_config::shared::_	+12.79 KiB	17
anon.f6b518799a8b19c7e356431bcdfa99c4.533.llvm.6184102975340891627	+12.29 KiB	1
anon.091bbad26cc3924e9c77bf8d4e018d37.513.llvm.16286174339815826116	-12.29 KiB	1
tracing_subscriber	-11.45 KiB	62
agent_data_plane_config::domains::dogstatsd	-10.43 KiB	13
anon.24f983bdb5d7a9f41626c5544756a394.180.llvm.10441113739384331192	+9.72 KiB	1
anon.61f4b4fd3b48a953f00eec7e253961a0.298.llvm.6300809537654130731	-9.72 KiB	1
anon.24f983bdb5d7a9f41626c5544756a394.882.llvm.10441113739384331192	+9.16 KiB	1
anon.61f4b4fd3b48a953f00eec7e253961a0.559.llvm.6300809537654130731	-9.15 KiB	1
serde_core	+8.68 KiB	97
anon.091bbad26cc3924e9c77bf8d4e018d37.4.llvm.16286174339815826116	-8.58 KiB	1
anon.2c9e2e2154d21bde9e49f2d4896e12f7.12.llvm.2573425551792850089	+8.40 KiB	1
serde_json	-7.94 KiB	113
smallvec	-7.74 KiB	30
anon.f6b518799a8b19c7e356431bcdfa99c4.392.llvm.6184102975340891627	+6.94 KiB	1

Detailed Symbol Changes

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  [NEW] +17.5Ki  [NEW]     +76    anon.24f983bdb5d7a9f41626c5544756a394.887.llvm.10441113739384331192
  [NEW] +14.0Ki  [NEW] +13.9Ki    agent_data_plane::state::metrics::rules::compat::get_compat_remappings::h19651ee55cb484c9
  [NEW] +12.3Ki  [NEW]     +81    anon.f6b518799a8b19c7e356431bcdfa99c4.533.llvm.6184102975340891627
  [NEW] +12.0Ki  [NEW] +11.9Ki    agent_data_plane::state::metrics::rules::dogstatsd::get_dogstatsd_remappings::hfb3b72311acf3cad
  [NEW] +9.72Ki  [NEW]     +79    anon.24f983bdb5d7a9f41626c5544756a394.180.llvm.10441113739384331192
  [NEW] +9.16Ki  [NEW]     +91    anon.24f983bdb5d7a9f41626c5544756a394.882.llvm.10441113739384331192
  [NEW] +8.40Ki  [NEW]     +81    anon.2c9e2e2154d21bde9e49f2d4896e12f7.12.llvm.2573425551792850089
  [NEW] +6.94Ki  [NEW]     +77    anon.f6b518799a8b19c7e356431bcdfa99c4.392.llvm.6184102975340891627
 -84.8% -6.73Ki -86.3% -6.73Ki    _<h2::client::Connection<T,B> as core::future::future::Future>::poll::h0f7c777c6a66efe3
  [DEL] -6.86Ki  [DEL]     -77    anon.091bbad26cc3924e9c77bf8d4e018d37.399.llvm.16286174339815826116
  [DEL] -7.08Ki  [DEL] -6.89Ki    serde_json::value::de::_<impl serde_core::de::Deserialize for serde_json::value::Value>::deserialize::h45fdda11a534df1b
  [DEL] -8.27Ki  [DEL] -8.18Ki    serde_core::ser::SerializeMap::serialize_entry::hcd94be53b1549835
  [DEL] -8.58Ki  [DEL]     -81    anon.091bbad26cc3924e9c77bf8d4e018d37.4.llvm.16286174339815826116
  [DEL] -9.15Ki  [DEL]     -91    anon.61f4b4fd3b48a953f00eec7e253961a0.559.llvm.6300809537654130731
  [DEL] -9.72Ki  [DEL]     -79    anon.61f4b4fd3b48a953f00eec7e253961a0.298.llvm.6300809537654130731
  [DEL] -12.3Ki  [DEL]     -81    anon.091bbad26cc3924e9c77bf8d4e018d37.513.llvm.16286174339815826116
  -1.1% -13.3Ki  -1.1% -13.3Ki    [section .gcc_except_table]
  [DEL] -14.8Ki  [DEL] -14.7Ki    agent_data_plane::state::metrics::rules::get_compat_remappings::hc7620de93b7e14a3
  [DEL] -17.5Ki  [DEL]     -76    anon.091bbad26cc3924e9c77bf8d4e018d37.460.llvm.16286174339815826116
 -98.1% -24.9Ki -98.5% -24.9Ki    agent_data_plane::state::metrics::rules::get_datadog_agent_remappings::h4ff388cc81845209
  -0.8% -83.5Ki  -0.6% -51.1Ki    [10166 Others]
  -0.3%  -132Ki  -0.3% -100.0Ki    TOTAL

[pr-commenter]

Regression Detector (Agent Data Plane)

Run ID: 4c63ab98-e19b-4926-a3ca-3e81fe8f5261
Baseline: 6825bb3d · Comparison: d601d0f9 · 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_heavy	memory	⚪ +0.36	metrics profiles logs
quality_gates_rss_idle	memory	⚪ +0.04	metrics profiles logs
quality_gates_rss_dsd_low	memory	⚪ -0.00	metrics profiles logs
quality_gates_rss_dsd_ultraheavy	memory	⚪ -0.11	metrics profiles logs
quality_gates_rss_dsd_medium	memory	⚪ -0.43	metrics profiles logs

Bounds Checks: ✅ Passed (5)

experiment	check	replicates	observed	links
quality_gates_rss_dsd_heavy	memory_usage	10/10	✅ 229 MiB ≤ 250 MiB	metrics profiles logs
quality_gates_rss_dsd_low	memory_usage	10/10	✅ 51.3 MiB ≤ 60 MiB	metrics profiles logs
quality_gates_rss_dsd_medium	memory_usage	10/10	✅ 91.7 MiB ≤ 100 MiB	metrics profiles logs
quality_gates_rss_dsd_ultraheavy	memory_usage	10/10	✅ 389 MiB ≤ 420 MiB	metrics profiles logs
quality_gates_rss_idle	memory_usage	10/10	✅ 31.9 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.

[datadog-prod-us1-4]

More details

The shared helper preserves the run command’s platform-specific signal branches and replay’s signal-to-cancellation transition. Its replay import and caller remain Linux-gated, so the extraction does not introduce a cross-platform compilation or shutdown-flow regression.

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