add target_info metric for each resource

[nikhilsinhaparseable]

add job and instance label to every metric
derive job from service.namespace/service.name and instance from service.instance.id
add metric target_info with data_point_value=1 per resource use latest data point timestamp

Summary by CodeRabbit

• New Features

  • Prometheus metrics include derived job and instance labels when service identity information is available.
  • Job labels can optionally include a namespace prefix.
  • Target metadata is exposed through a target_info metric with the latest metric timestamp.
  • Derived service identity labels take precedence over conflicting labels from other metric sources.
  • Metrics remain available with empty identity labels when service identity information is incomplete.

• Bug Fixes

  • target_info is no longer emitted for resources without metric data points.

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No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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• src/otel/metrics.rs

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Walkthrough

OTel metric processing now emits target_info only when resource identity and a real data-point timestamp exist. Empty gauges no longer use the epoch timestamp or emit target_info.

Changes

OTel target metadata

Layer / File(s)	Summary
Require a data-point timestamp for target_info src/otel/metrics.rs	Metric processing removes has_metrics tracking, retains the greatest data-point timestamp, and requires that timestamp before emitting target_info.
Validate empty metric behavior src/otel/metrics.rs	A regression test confirms that an identity-bearing resource with an empty gauge emits no target_info record.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to d4dfb

OTel target metadata is now omitted when no metric data point supplies a timestamp, preventing timestamp-less target_info records. The current change has no remaining actionable merge risk.

Suggested reviewers: parmesant

Poem

A rabbit checks the timestamp trail
No epoch ghost can tip the scale
Empty gauges stay unseen
Target info remains clean
Tests hop brightly through the vale

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 12 functions across 1 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the addition of the target_info metric, which is a central part of the changes. It does not mention the new job and instance labels, but the title does not need to c…
Description check	✅ Passed	The description explains the new labels, their sources, and the target_info metric behavior. It omits the template heading, issue reference, testing checklist, comments checklist, and documentation …
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.

Full details: Title check

Explanation

The title clearly identifies the addition of the target_info metric, which is a central part of the changes. It does not mention the new job and instance labels, but the title does not need to cover every change.

Full details: Description check

Explanation

The description explains the new labels, their sources, and the target_info metric behavior. It omits the template heading, issue reference, testing checklist, comments checklist, and documentation checklist, but it provides the main intent and scope of the pull request.

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Actionable comments posted: 1

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Inline comments:
In `@src/otel/metrics.rs`:
- Line 777: Update the target timestamp fallback at the target_timestamp
handling site to use a fixed Unix epoch timestamp when no data-point timestamp
exists, rather than calling convert_epoch_nano_to_timestamp(0). Preserve the
existing target_timestamp value when present and ensure empty Gauge resources
emit a stable epoch timestamp.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Essentials

Run ID: 7a865c68-5dc8-4cca-9812-91f37d17dca1

📥 Commits

Reviewing files that changed from the base of the PR and between 91c062f and e282852.

📒 Files selected for processing (1)

• src/otel/metrics.rs

Included review availability: Your plan provides up to 8 included reviews per hour; 7 remain after this review.