diff --git a/crates/tranquil-store/src/gauntlet/leak.rs b/crates/tranquil-store/src/gauntlet/leak.rs
new file mode 100644
index 0000000..981131b
--- /dev/null
+++ b/crates/tranquil-store/src/gauntlet/leak.rs
@@ -0,0 +1,236 @@
+use std::num::NonZeroU64;
+use std::time::Duration;
+
+use serde::{Deserialize, Serialize};
+
+use super::metrics::{MetricName, MetricsSample};
+
+#[derive(Debug, Clone, Copy, Serialize, Deserialize)]
+pub struct LeakGateConfig {
+    pub warmup_ms: u64,
+    pub window_ms: NonZeroU64,
+    pub growth_limit_pct: f64,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct LeakGateBuildError(pub &'static str);
+
+impl std::fmt::Display for LeakGateBuildError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str(self.0)
+    }
+}
+
+impl std::error::Error for LeakGateBuildError {}
+
+impl LeakGateConfig {
+    pub fn try_new(
+        warmup_ms: u64,
+        window_ms: u64,
+        growth_limit_pct: f64,
+    ) -> Result<Self, LeakGateBuildError> {
+        let window_ms = NonZeroU64::new(window_ms)
+            .ok_or(LeakGateBuildError("leak gate window_ms must be > 0"))?;
+        if !growth_limit_pct.is_finite() || growth_limit_pct < 0.0 {
+            return Err(LeakGateBuildError(
+                "leak gate growth_limit_pct must be finite and non-negative",
+            ));
+        }
+        Ok(Self {
+            warmup_ms,
+            window_ms,
+            growth_limit_pct,
+        })
+    }
+
+    pub fn standard() -> Self {
+        Self::try_new(60 * 60 * 1_000, 4 * 60 * 60 * 1_000, 5.0)
+            .expect("standard leak gate config is valid")
+    }
+
+    pub fn short_for_tests() -> Self {
+        Self::try_new(60_000, 4 * 60_000, 5.0).expect("short_for_tests leak gate config is valid")
+    }
+
+    pub fn warmup(&self) -> Duration {
+        Duration::from_millis(self.warmup_ms)
+    }
+
+    pub fn window(&self) -> Duration {
+        Duration::from_millis(self.window_ms.get())
+    }
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct LeakViolation {
+    pub metric: String,
+    pub start_ms: u64,
+    pub end_ms: u64,
+    pub start_value: u64,
+    pub end_value: u64,
+    pub growth_pct: f64,
+    pub limit_pct: f64,
+}
+
+pub fn evaluate(samples: &[MetricsSample], cfg: LeakGateConfig) -> Vec<LeakViolation> {
+    if samples.len() < 2 {
+        return Vec::new();
+    }
+    MetricName::ALL
+        .iter()
+        .flat_map(|&m| evaluate_metric(samples, m, cfg))
+        .collect()
+}
+
+fn evaluate_metric(
+    samples: &[MetricsSample],
+    metric: MetricName,
+    cfg: LeakGateConfig,
+) -> Option<LeakViolation> {
+    let post_warmup: Vec<&MetricsSample> = samples
+        .iter()
+        .filter(|s| s.elapsed_ms >= cfg.warmup_ms)
+        .collect();
+    if post_warmup.len() < 2 {
+        return None;
+    }
+
+    let min_delta = metric.min_absolute_delta();
+    let window = cfg.window_ms.get();
+    let mut worst: Option<LeakViolation> = None;
+    for (i, start) in post_warmup.iter().enumerate() {
+        let Some(start_v) = start.metric(metric) else {
+            continue;
+        };
+        if start_v == 0 {
+            continue;
+        }
+        let deadline = start.elapsed_ms.saturating_add(window);
+        for end in post_warmup.iter().skip(i + 1) {
+            if end.elapsed_ms > deadline {
+                break;
+            }
+            let Some(end_v) = end.metric(metric) else {
+                continue;
+            };
+            if end_v <= start_v {
+                continue;
+            }
+            let delta = end_v - start_v;
+            if delta < min_delta {
+                continue;
+            }
+            let growth = (delta as f64 / start_v as f64) * 100.0;
+            if growth <= cfg.growth_limit_pct {
+                continue;
+            }
+            let candidate = LeakViolation {
+                metric: metric.as_str().to_string(),
+                start_ms: start.elapsed_ms,
+                end_ms: end.elapsed_ms,
+                start_value: start_v,
+                end_value: end_v,
+                growth_pct: growth,
+                limit_pct: cfg.growth_limit_pct,
+            };
+            match &worst {
+                Some(w) if w.growth_pct >= candidate.growth_pct => {}
+                _ => worst = Some(candidate),
+            }
+        }
+    }
+    worst
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const GIB: u64 = 1024 * 1024 * 1024;
+
+    fn sample(elapsed_ms: u64, rss: u64) -> MetricsSample {
+        MetricsSample {
+            elapsed_ms,
+            rss_bytes: Some(rss),
+            fd_count: Some(10),
+            data_dir_bytes: 0,
+            index_dir_bytes: 0,
+            segments_dir_bytes: 0,
+            data_file_count: Some(0),
+            segment_count: Some(0),
+            block_index_entries: 0,
+            hint_file_bytes: 0,
+        }
+    }
+
+    #[test]
+    fn flat_metrics_no_violation() {
+        let cfg = LeakGateConfig::short_for_tests();
+        let series: Vec<MetricsSample> = (0..20)
+            .map(|i| sample(60_000 + i * 60_000, GIB))
+            .collect();
+        assert!(evaluate(&series, cfg).is_empty());
+    }
+
+    #[test]
+    fn growing_rss_flagged() {
+        let cfg = LeakGateConfig::short_for_tests();
+        let series: Vec<MetricsSample> = (0..20)
+            .map(|i| sample(60_000 + i * 60_000, GIB + i * 64 * 1024 * 1024))
+            .collect();
+        let v = evaluate(&series, cfg);
+        assert!(!v.is_empty());
+        assert_eq!(v[0].metric, "rss_bytes");
+        assert!(v[0].growth_pct > 5.0);
+    }
+
+    #[test]
+    fn warmup_samples_ignored() {
+        let cfg = LeakGateConfig::short_for_tests();
+        let mut series: Vec<MetricsSample> = Vec::new();
+        series.push(sample(10_000, 1));
+        series.push(sample(30_000, GIB));
+        (0..10).for_each(|i| {
+            series.push(sample(60_000 + i * 60_000, GIB));
+        });
+        assert!(evaluate(&series, cfg).is_empty());
+    }
+
+    #[test]
+    fn window_bound_honored() {
+        let cfg = LeakGateConfig::try_new(0, 2 * 60_000, 5.0).unwrap();
+        let series = vec![sample(0, GIB), sample(200_000, 2 * GIB)];
+        assert!(
+            evaluate(&series, cfg).is_empty(),
+            "200s gap exceeds 120s window, growth must not be flagged"
+        );
+    }
+
+    #[test]
+    fn small_absolute_delta_not_flagged() {
+        let cfg = LeakGateConfig::short_for_tests();
+        let series: Vec<MetricsSample> = (0..10)
+            .map(|i| sample(60_000 + i * 60_000, GIB + i * 1024))
+            .collect();
+        assert!(
+            evaluate(&series, cfg).is_empty(),
+            "kilobyte growth is below the RSS absolute-delta floor"
+        );
+    }
+
+    #[test]
+    fn missing_metric_samples_skipped() {
+        let cfg = LeakGateConfig::short_for_tests();
+        let mut series: Vec<MetricsSample> = (0..10)
+            .map(|i| sample(60_000 + i * 60_000, GIB))
+            .collect();
+        series[3].rss_bytes = None;
+        series[7].rss_bytes = None;
+        assert!(evaluate(&series, cfg).is_empty());
+    }
+
+    #[test]
+    fn zero_window_rejected_at_construction() {
+        assert!(LeakGateConfig::try_new(0, 0, 5.0).is_err());
+    }
+}
diff --git a/crates/tranquil-store/src/gauntlet/metrics.rs b/crates/tranquil-store/src/gauntlet/metrics.rs
new file mode 100644
index 0000000..4b58317
--- /dev/null
+++ b/crates/tranquil-store/src/gauntlet/metrics.rs
@@ -0,0 +1,247 @@
+use std::path::Path;
+use std::sync::Arc;
+use std::time::Duration;
+
+use serde::{Deserialize, Serialize};
+use tracing::warn;
+
+use super::runner::{EventLogState, Harness};
+use crate::blockstore::TranquilBlockStore;
+use crate::io::StorageIO;
+
+#[derive(Debug, Clone, Copy, Serialize, Deserialize)]
+pub struct MetricsSample {
+    pub elapsed_ms: u64,
+    pub rss_bytes: Option<u64>,
+    pub fd_count: Option<u64>,
+    pub data_dir_bytes: u64,
+    pub index_dir_bytes: u64,
+    pub segments_dir_bytes: u64,
+    pub data_file_count: Option<u64>,
+    pub segment_count: Option<u64>,
+    pub block_index_entries: u64,
+    pub hint_file_bytes: u64,
+}
+
+impl MetricsSample {
+    pub fn metric(&self, name: MetricName) -> Option<u64> {
+        match name {
+            MetricName::RssBytes => self.rss_bytes,
+            MetricName::FdCount => self.fd_count,
+            MetricName::DataDirBytes => Some(self.data_dir_bytes),
+            MetricName::IndexDirBytes => Some(self.index_dir_bytes),
+            MetricName::SegmentsDirBytes => Some(self.segments_dir_bytes),
+            MetricName::DataFileCount => self.data_file_count,
+            MetricName::SegmentCount => self.segment_count,
+            MetricName::BlockIndexEntries => Some(self.block_index_entries),
+            MetricName::HintFileBytes => Some(self.hint_file_bytes),
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub enum MetricName {
+    RssBytes,
+    FdCount,
+    DataDirBytes,
+    IndexDirBytes,
+    SegmentsDirBytes,
+    DataFileCount,
+    SegmentCount,
+    BlockIndexEntries,
+    HintFileBytes,
+}
+
+impl MetricName {
+    pub const ALL: &'static [MetricName] = &[
+        Self::RssBytes,
+        Self::FdCount,
+        Self::DataDirBytes,
+        Self::IndexDirBytes,
+        Self::SegmentsDirBytes,
+        Self::DataFileCount,
+        Self::SegmentCount,
+        Self::BlockIndexEntries,
+        Self::HintFileBytes,
+    ];
+
+    pub const fn as_str(self) -> &'static str {
+        match self {
+            Self::RssBytes => "rss_bytes",
+            Self::FdCount => "fd_count",
+            Self::DataDirBytes => "data_dir_bytes",
+            Self::IndexDirBytes => "index_dir_bytes",
+            Self::SegmentsDirBytes => "segments_dir_bytes",
+            Self::DataFileCount => "data_file_count",
+            Self::SegmentCount => "segment_count",
+            Self::BlockIndexEntries => "block_index_entries",
+            Self::HintFileBytes => "hint_file_bytes",
+        }
+    }
+
+    pub const fn min_absolute_delta(self) -> u64 {
+        match self {
+            Self::RssBytes => 16 * 1024 * 1024,
+            Self::FdCount => 16,
+            Self::DataDirBytes => 16 * 1024 * 1024,
+            Self::IndexDirBytes => 1024 * 1024,
+            Self::SegmentsDirBytes => 16 * 1024 * 1024,
+            Self::DataFileCount => 16,
+            Self::SegmentCount => 4,
+            Self::BlockIndexEntries => 1024,
+            Self::HintFileBytes => 1024 * 1024,
+        }
+    }
+}
+
+pub fn sample_harness<S: StorageIO + Send + Sync + 'static>(
+    harness: &Harness<S>,
+    elapsed: Duration,
+) -> MetricsSample {
+    MetricsSample {
+        elapsed_ms: u64::try_from(elapsed.as_millis()).unwrap_or(u64::MAX),
+        rss_bytes: read_rss(),
+        fd_count: count_open_fds(),
+        data_dir_bytes: dir_bytes(harness.store.data_dir()),
+        index_dir_bytes: dir_bytes(harness.store.block_index().index_dir()),
+        segments_dir_bytes: harness
+            .eventlog
+            .as_ref()
+            .map(|el| dir_bytes(&el.segments_dir))
+            .unwrap_or(0),
+        data_file_count: data_file_count(&harness.store),
+        segment_count: harness.eventlog.as_ref().and_then(segment_count),
+        block_index_entries: harness.store.block_index().approximate_block_count(),
+        hint_file_bytes: hint_bytes(harness.store.data_dir()),
+    }
+}
+
+fn data_file_count<S: StorageIO + Send + Sync + 'static>(
+    store: &Arc<TranquilBlockStore<S>>,
+) -> Option<u64> {
+    match store.list_data_files() {
+        Ok(v) => Some(v.len() as u64),
+        Err(e) => {
+            warn!(error = %e, "gauntlet metrics: list_data_files failed");
+            None
+        }
+    }
+}
+
+fn segment_count<S: StorageIO + Send + Sync + 'static>(el: &EventLogState<S>) -> Option<u64> {
+    match el.manager.list_segments() {
+        Ok(v) => Some(v.len() as u64),
+        Err(e) => {
+            warn!(error = %e, "gauntlet metrics: list_segments failed");
+            None
+        }
+    }
+}
+
+fn dir_bytes(path: &Path) -> u64 {
+    let Ok(entries) = std::fs::read_dir(path) else {
+        return 0;
+    };
+    entries
+        .filter_map(Result::ok)
+        .map(|entry| match entry.file_type() {
+            Ok(ft) if ft.is_dir() => dir_bytes(&entry.path()),
+            Ok(_) => entry.metadata().map(|m| m.len()).unwrap_or(0),
+            Err(_) => 0,
+        })
+        .sum()
+}
+
+fn hint_bytes(data_dir: &Path) -> u64 {
+    let Ok(entries) = std::fs::read_dir(data_dir) else {
+        return 0;
+    };
+    entries
+        .filter_map(Result::ok)
+        .filter(|entry| {
+            entry
+                .path()
+                .extension()
+                .and_then(|e| e.to_str())
+                .map(|e| e == "tqh")
+                .unwrap_or(false)
+        })
+        .map(|entry| entry.metadata().map(|m| m.len()).unwrap_or(0))
+        .sum()
+}
+
+#[cfg(target_os = "linux")]
+fn read_rss() -> Option<u64> {
+    let status = match std::fs::read_to_string("/proc/self/status") {
+        Ok(s) => s,
+        Err(e) => {
+            warn!(error = %e, "gauntlet metrics: read /proc/self/status failed");
+            return None;
+        }
+    };
+    let parsed = status.lines().find_map(|line| {
+        let rest = line.strip_prefix("VmRSS:")?;
+        let kb: u64 = rest.split_whitespace().next()?.parse().ok()?;
+        Some(kb * 1024)
+    });
+    if parsed.is_none() {
+        warn!("gauntlet metrics: VmRSS line missing from /proc/self/status");
+    }
+    parsed
+}
+
+#[cfg(not(target_os = "linux"))]
+fn read_rss() -> Option<u64> {
+    None
+}
+
+#[cfg(target_os = "linux")]
+fn count_open_fds() -> Option<u64> {
+    match std::fs::read_dir("/proc/self/fd") {
+        Ok(entries) => Some(entries.filter_map(Result::ok).count() as u64),
+        Err(e) => {
+            warn!(error = %e, "gauntlet metrics: read /proc/self/fd failed");
+            None
+        }
+    }
+}
+
+#[cfg(not(target_os = "linux"))]
+fn count_open_fds() -> Option<u64> {
+    None
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn metric_names_roundtrip_strings() {
+        MetricName::ALL.iter().for_each(|m| {
+            let s = m.as_str();
+            assert!(!s.is_empty());
+        });
+    }
+
+    #[test]
+    #[cfg_attr(not(target_os = "linux"), ignore = "linux /proc only")]
+    fn rss_reads_nonzero() {
+        let rss = read_rss().expect("rss");
+        assert!(rss > 0, "rss should be positive, got {rss}");
+    }
+
+    #[test]
+    #[cfg_attr(not(target_os = "linux"), ignore = "linux /proc only")]
+    fn fd_count_reads_nonzero() {
+        let fd = count_open_fds().expect("fd");
+        assert!(fd > 0);
+    }
+
+    #[test]
+    fn dir_bytes_sums_entries() {
+        let dir = tempfile::TempDir::new().unwrap();
+        std::fs::write(dir.path().join("a"), b"1234").unwrap();
+        std::fs::write(dir.path().join("b"), b"5678").unwrap();
+        assert_eq!(dir_bytes(dir.path()), 8);
+    }
+}