PrometheusRecorder (src/prometheus.rs)

! Prometheus text exposition for captured metrics (zero external deps).

// Source: https://github.com/qntx/bot | License: Apache-2.0 | Copyright 2025 QuantX
// Provided via justclaw.it.com; keep this notice with the code.
//! Prometheus text exposition for captured metrics (zero external deps).

use std::collections::{BTreeMap, BTreeSet};
use std::fmt::Write as _;
use std::sync::Mutex;

use crate::metrics::MetricsSink;

type LabelSet = Vec<(String, String)>;
type SeriesKey = (String, LabelSet);

/// Metrics sink that accumulates samples and can render Prometheus text format 0.0.4.
#[derive(Debug, Default)]
pub struct PrometheusRecorder {
    counters: Mutex<BTreeMap<SeriesKey, u64>>,
    histograms: Mutex<BTreeMap<SeriesKey, Vec<f64>>>,
    gauges: Mutex<BTreeMap<SeriesKey, f64>>,
}

impl PrometheusRecorder {
    /// Empty recorder.
    #[must_use]
    pub fn 

... (truncated -- full source via MCP)