fix(function-autoscaler): record utilization data age

[borao]

TL;DR

Record the age of the newest utilization sample after the autoscaler produces a scaling decision, making the documented histogram observable.

Additional Details

• Retain the newest raw utilization timestamp.
• Emit nvcf_autoscaler.processing.utilization_data_age_milliseconds only for real scaling decisions.
• Skip empty utilization data and clamp future timestamps to zero using saturating arithmetic.
• Add regression coverage for timestamp retention and age calculation.

For the Reviewer

Please focus on the timestamp units and metric emission point in work/mod.rs.

For QA

Passed locally:

• cargo clippy -p rs-autoscaler --all-targets -- -D warnings
• cargo test -p rs-autoscaler (158 passed, 10 ignored)
• git diff --check

cargo fmt -p rs-autoscaler --check still reports pre-existing formatting drift in work/discovery.rs and unrelated sections of work/mod.rs; the new lines are formatted and that unrelated drift is excluded from this PR.

Issues

Relates to #15

Checklist

• I am familiar with the Contributing Guidelines.
• I have signed off my commits for Developer Certificate of Origin (DCO) compliance.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

Summary by CodeRabbit

• Bug Fixes
  • Autoscaling now tracks the latest utilization timestamp.
  • Utilization data age is calculated safely, including future timestamps and missing data.
  • Added coverage to verify timestamp propagation and age calculations.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 0704987 and 0f6f1bd.

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• src/control-plane-services/function-autoscaler/crates/server/src/work/mod.rs

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📝 Walkthrough

Walkthrough

The autoscaler now retains the newest utilization timestamp, calculates its non-negative age in milliseconds, and records that age when data is available. Tests cover timestamp propagation, missing timestamps, and future timestamps.

Changes

Utilization age tracking

Layer / File(s)	Summary
Utilization timestamp propagation src/control-plane-services/function-autoscaler/crates/server/src/work/mod.rs	GatheredScalingInputs retains the newest timestamp from raw utilization samples. Worker-path tests verify propagation.
Utilization age calculation and recording src/control-plane-services/function-autoscaler/crates/server/src/work/mod.rs	The autoscaler converts timestamp age to milliseconds, clamps future data to zero, returns None for missing data, and records available age values. Tests cover these cases.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix

Suggested reviewers: along-2017

Merge Risk: ⚪ Minimal · up to 0f6f1

The change records utilization-data age only for completed scaling decisions and safely handles missing or future timestamps, with no concrete merge-blocking risk identified.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title uses valid Conventional Commits syntax and accurately describes the change. The scoped fix type is appropriate for adding the missing utilization-age recording behavior.
Docstring Coverage	✅ Passed	Docstring coverage is 87.50% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 8 functions across 1 files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/function-autoscaler/record-utilization-data-age

Warning

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🔧 Clippy (1.98.0)

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[github-actions]

🛡️ CodeQL Analysis

🚨 Found 5 issue(s)

Severity Breakdown:

• 🔴 Errors: 0
• 🟡 Warnings: 0
• 🔵 Notes: 0

📋 Top Issues

🔗 View full details in Security tab

_{🕐 Last updated: 2026-09-14 22:22:25 UTC | Commit: 0f6f1bd}

[dmikhaylovnv]

LGTM

[balajinvda]

🎉 This PR is included in version nvcf-function-autoscaler-v1.21.7 🎉

The release is available on GitHub release

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