Bug Description

In storage/remote/otlptranslator/prometheusremotewrite/number_data_points.go, the addSumNumberDataPoints function silently swallows errors from createAttributes:

lbls, err := c.createAttributes(
    pt.Attributes(),
    settings,
    nil,
    true,
    meta,
    model.MetricNameLabel,
    meta.MetricFamilyName,
)
if err != nil {
    return nil  // BUG: should be "return err"
}

https://github.com/prometheus/prometheus/blob/main/storage/remote/otlptranslator/prometheusremotewrite/number_data_points.go#L88-L89

Compare with addGaugeNumberDataPoints in the same file which correctly returns the error:

if err != nil {
    return err
}

https://github.com/prometheus/prometheus/blob/main/storage/remote/otlptranslator/prometheusremotewrite/number_data_points.go#L47-L48

Impact

When createAttributes fails for sum metrics, the error is silently discarded and processing continues. This could lead to:

• Silent data loss (sum metrics not being written)
• Difficult-to-debug issues in OTLP ingestion pipelines

Root Cause

The bug was introduced in #16951 during a refactor. The original code had return err, but it was accidentally changed to return nil.

Suggested Fix

 if err != nil {
-    return nil
+    return err
 }