Replace Vec::remove(0) (O(n) per-sample buffer shift -> O(n^2) full-window
sweep) with VecDeque push_back/pop_front (O(1) eviction) in the fixed-length
sliding/ring buffers of the vital-sign and wifiscan extractors. Where the
autocorrelation / zero-crossing / Pearson loop needs a contiguous slice,
make_contiguous() is called once per extract(), matching the idiom already used
in wifiscan/pipeline/orchestrator.rs. Output is bit-identical.
Sites: anomaly.rs (rr/hr history), store.rs (readings ring; history() now takes
&mut self to hand back a contiguous slice, no external callers), wifiscan
breathing_extractor.rs (filtered history), wifiscan correlator.rs (per-BSSID
histories -> Vec<VecDeque<f32>>). (heartrate.rs/breathing.rs windows land with
the §A2/§A3 fixes in a separate commit.)
New criterion bench crates/wifi-densepose-vitals/benches/vitals_bench.rs drives
each extractor over a full-window fill. Honest MEASURED result: end-to-end win
is NULL within noise at realistic ESP32 window sizes (1500-3000) because the
per-frame DSP dominates the eviction (heartrate 42.8ms->44.4ms, breathing
7.95ms->7.86ms, overlapping CIs). In isolation the eviction collapses O(n^2)
-> O(n) (34.6x at window=3000, 3158x at window=100000); A1 lands as the correct
data structure removing a latent O(n^2), NOT a claimed hot-path speedup.
Reproduce: cargo bench -p wifi-densepose-vitals --bench vitals_bench
Co-Authored-By: claude-flow <ruv@ruv.net>
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