Module alloc_budget 

Allocation budget: sequential leak detection using CUSUM + e-process.

Tracks allocation counts (or bytes) per frame as a time series and detects sustained drift (allocation leaks or regressions) with formal, anytime-valid guarantees.

Detectors

1. CUSUM — Cumulative Sum control chart for fast mean-shift detection. Sensitive to small, sustained drifts. Signals when the cumulative deviation from the reference mean exceeds a threshold.

2. E-process — Anytime-valid sequential test (test martingale). Provides a p-value-like guarantee that holds under optional stopping: P(E_t ever exceeds 1/α | H₀) ≤ α (Ville’s inequality).

Usage

use ftui_render::alloc_budget::{AllocLeakDetector, LeakDetectorConfig};

let config = LeakDetectorConfig::default();
let mut detector = AllocLeakDetector::new(config);

// Feed allocation counts per frame.
for count in [100, 102, 98, 105, 101] {
    let alert = detector.observe(count as f64);
    assert!(!alert.triggered);
}

Evidence Ledger

Every observation produces an EvidenceEntry recording the residual, CUSUM state, and e-process value. This ledger is inspectable for diagnostics and can be serialised to JSONL.

Failure Modes

• False positive: bounded by α (default 0.05). Under H₀ (no leak), the e-process triggers with probability ≤ α across all stopping times.
• Detection delay: CUSUM detects a shift of δ within approximately h / δ frames (where h is the threshold). E-process provides complementary evidence with stronger guarantees.

Structs

AllocLeakDetector

Sequential allocation leak detector combining CUSUM and e-process.

EvidenceEntry

A single observation’s evidence record.

LeakAlert

Result of a single observation.

LeakDetectorConfig

Configuration for the allocation leak detector.