fix: restore reserved suffix stripping in PrometheusNaming.sanitizeMetricName()

[Copilot]

sanitizeMetricName() was simplified in 1.6.0 to return its input unchanged (since any non-empty UTF-8 string is now a valid metric name). This silently broke downstream tools — notably the JMX Exporter and the simpleclient bridge — that call sanitizeMetricName to normalize external names before passing them to snapshot builders.

The missing stripping means a JMX attribute that produces kafka_consumer_request_total as a raw name is no longer sanitized to kafka_consumer_request. With inferCounterTypeFromName: true this triggers unintended counter-type inference; with it false the metric is stored under the wrong name, breaking exact-name registry lookups.

Changes

• PrometheusNaming.java — restore RESERVED_METRIC_NAME_SUFFIXES constant and the iterative suffix-stripping loop in sanitizeMetricName(). The exact-match case (where the entire input is a reserved suffix, e.g. "_total" → "total") is handled in a dedicated pre-pass before the stripping loop, and the inner loop now breaks immediately after a match to restart cleanly.

• PrometheusNamingTest.java — update expectations to match restored behaviour; add a regression test for the JMX Exporter scenario and the dot-variant corner case (.total).

• MetricMetadataTest.java — update expectations accordingly.

// Before fix (1.6.x): suffix preserved → metric stored as "kafka_consumer_request_total"
PrometheusNaming.sanitizeMetricName("kafka_consumer_request_total");
// → "kafka_consumer_request_total"  ← breaks name-based lookups, triggers counter inference

// After fix: suffix stripped → metric stored as "kafka_consumer_request"
PrometheusNaming.sanitizeMetricName("kafka_consumer_request_total");
// → "kafka_consumer_request"

Note: Counter.builder().name("events_total") is unaffected — the builder API does not go through sanitizeMetricName.

Warning

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• checkstyle.org
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