The PromQL layer only had a fixed-width histogram() (per-bucket counts), with no way to ask for p50/p95/p99. Adds histogram_quantile(p, metric[range]), interpolating over each series's retained raw sample values (linear interpolation between closest ranks) rather than building a separate pre-aggregated bucketed-histogram representation — exact for the data actually kept. An optional bracketed range narrows the computation to a trailing window, mirroring rate()'s range selector. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01TeyhRfMYjMditek6geDRoQ