feat(observability): gated histogram buckets for firefly.* + honest exemplars doc#9
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casc84ab merged 1 commit intoJul 16, 2026
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…xemplars doc Add management.metrics.distribution.percentiles-histogram.firefly, gated by FIREFLY_OBSERVABILITY_METRICS_HISTOGRAMS_ENABLED and DEFAULT OFF. When enabled it applies a Micrometer MeterFilter to every firefly.* meter so p99 becomes aggregable across pods (histogram_quantile()) and metric→trace exemplars can anchor to _bucket samples. Ships inert so there is no cardinality impact until the platform opts in; the client-side publishPercentiles are unaffected. Also correct the ExemplarsAutoConfiguration Javadoc: exemplars are NOT functional in the current scrape→collector→store pipeline (no buckets by default, 0.0.4 exposition, exemplars dropped in transit). Stop promising metric→trace click-through and document the three unmet preconditions.
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July 16, 2026 10:23
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Response to the observability master document (metrics findings M3/M4).
M3 — histogram buckets (gated, default OFF)
firefly.*timers/summaries publish client-side percentiles only, with nolebuckets, so p99 is not aggregable across pods andhistogram_quantile()is impossible. This addsmanagement.metrics.distribution.percentiles-histogram.firefly, driven byFIREFLY_OBSERVABILITY_METRICS_HISTOGRAMS_ENABLED(default false).MeterFilter); the timer/summary builders are untouched.publishPercentilesgauges are unaffected.M4 — honest exemplars doc
ExemplarsAutoConfigurationis an empty marker and the scrape→collector→store pipeline drops OpenMetrics exemplars, so metric→trace click-through does not work today. The Javadoc now says so and lists the three unmet preconditions instead of promising jump-to-trace.No behavioural change on default config.