feat(perf,benchmark-infra): criterion bench harness + advisory CI workflows (SDD-120)

Implementation of SDD-120 §1-§8:

Bench harness (crates/chanora_audio/benches/):
- common.rs: deterministic synthetic audio (440 Hz sine, no RNG).
- realtime_capture.rs: bench_capture_alloc_count (dhat) +
  bench_capture_callback_wall_clock (criterion).
- opus_codec.rs: bench_opus_encode_latency + bench_opus_decode_latency
  (direct audiopus, not AudioHandler — SDD-120 §3 item 4).
- resampler.rs: bench_resampler_throughput across 44.1->48 /
  16->48 / 48->48 passthrough.

CI tooling (crates/chanora_audio/examples/):
- emit_baseline.rs: aggregates criterion estimates.json outputs
  into the SRS-217 baseline schema.
- compare_baseline.rs: applies SRS-219 tolerance, renders markdown
  table with 🟢/🟡/🔴 markers + yellow simpler-form realization per
  SDD-120 §8.

  Deviation from SDD-120 §2 / §5 / §7 placement: these tools live
  under examples/, not benches/ or src/bin/. Rationale: they must
  consume serde_json (a dev-only dep — production builds must not
  pull it). Cargo only resolves dev-dependencies for [[test]],
  [[bench]], and [[example]] targets; [[bin]] targets under
  src/bin/ see only regular [dependencies]. examples/ keeps the
  binaries out of the production dep tree while still giving them
  cargo run --example invocation. An SDD-120 amendment should
  reflect this.

Workflows (.github/workflows/):
- bench-advisory.yml: PR + push triggers; runs benches; posts a
  sticky PR comment via actions/github-script@v7; job status is
  always success (SRS-218 clause 4 — non-blocking).
- bench-baseline-update.yml: workflow_dispatch only; runs benches;
  opens PR via peter-evans/create-pull-request@v6 (sole writer of
  the SAD-089 baseline JSON).

Cargo.toml additions ([dev-dependencies] only — verified excluded
from --release builds): criterion 0.5, dhat 0.3, serde_json 1.

Source-code seam: minimal pub-but-#[doc(hidden)] bench_seam module
in chanora_audio (engine.rs + lib.rs re-export) so the criterion
bench harness can construct a CaptureState and drive
CaptureState::ingest without re-implementing the engine (SDD-120
§3). Non-iOS targets only — CaptureState itself is iOS-gated.

Initial baseline seed: crates/chanora_audio/benches/baselines/
x86_64-unknown-linux-gnu.json = {}. compare_baseline handles the
missing-baseline case gracefully and emits a 'no red markers'
report; the first manual dispatch of bench-baseline-update.yml
after merge establishes the real values.

Out of scope per SDD-120 §10: production telemetry export,
build-failing hard CI gate, multi-host benchmarking, IDE
integration, Dart-side bridge round-trip bench.

Verification:
- cargo check --workspace --all-targets: PASS.
- cargo bench --bench realtime_capture --no-run: PASS.
- cargo bench --bench opus_codec --no-run: PASS.
- cargo bench --bench resampler --no-run: PASS.
- cargo build --example emit_baseline --example compare_baseline
  -p chanora_audio: PASS.
- cargo test --workspace: 106 passed, 0 failed, 3 ignored — no
  regression from prior count.

crates/chanora_audio/Cargo.toml

@@ -90,6 +90,34 @@ tokio = { version = "1", features = ["sync", "rt", "macros", "time", "test-util"
 # Cross-platform recording Layer for the SDD-090 / DEC-027 privacy
 # invariant integration test (`tests/ptt_privacy.rs`).
 tracing-subscriber = { version = "0.3", features = ["registry"] }
+# SDD-120 §3 — criterion bench harness (realtime_capture / opus_codec /
+# resampler). `harness = false` per bench entry below disables the
+# default libtest harness so criterion can install its own.
+criterion = "0.5"
+# SDD-120 §3 item 1 — dhat is used as the global allocator inside
+# `benches/realtime_capture.rs` to count post-warmup heap allocations
+# on the realtime capture path. Dev-dep only — does NOT affect
+# production builds.
+dhat = "0.3"
+# SDD-120 §5 / §8 — JSON serialization for `emit_baseline` /
+# `compare_baseline` binaries that consume criterion's per-bench
+# `estimates.json` outputs and emit the SRS-217 baseline schema.
+serde_json = "1"
+
+[[bench]]
+name = "realtime_capture"
+harness = false
+path = "benches/realtime_capture.rs"
+
+[[bench]]
+name = "opus_codec"
+harness = false
+path = "benches/opus_codec.rs"
+
+[[bench]]
+name = "resampler"
+harness = false
+path = "benches/resampler.rs"
 
 [target.'cfg(target_os = "linux")'.dependencies]
 # GNOME-on-Wayland Global Push-to-Talk uses the freedesktop

crates/chanora_audio/benches/baselines/x86_64-unknown-linux-gnu.json

@@ -0,0 +1 @@
+{}

crates/chanora_audio/benches/common.rs

@@ -0,0 +1,57 @@
+// SDD-120 §4 — deterministic synthetic input generation.
+//
+// Shared by the three bench files (`realtime_capture.rs`,
+// `opus_codec.rs`, `resampler.rs`). Included via `mod common;` in
+// each bench file because criterion bench files compile as
+// independent binaries — there is no shared crate boundary between
+// them and `common.rs` is NOT registered as a `[[bench]]` entry.
+//
+// Determinism is load-bearing for §5 baseline stability: a 440 Hz
+// sine at amplitude 0.5 over the 48 kHz mixer rate, no RNG, no
+// fade-in, no DC offset. Same input bytes across runs and hosts.
+#![allow(dead_code)]
+
+use std::f32::consts::PI;
+
+/// Frame count of one 20 ms Opus frame at 48 kHz mono — matches
+/// `chanora_audio::engine::FRAME_SAMPLES` (private constant; the
+/// value `960` is fixed by the Opus codec protocol and SAD-088).
+pub const FRAME_SAMPLES: usize = 960;
+
+/// 48 kHz mixer rate — matches `chanora_audio::engine::SAMPLE_RATE`.
+pub const SAMPLE_RATE: u32 = 48_000;
+
+/// Interleaved synthetic capture buffer. For multi-channel layouts
+/// the same scalar value is replicated across each frame's channels
+/// (matches cpal's interleaved `Stream` data layout).
+pub fn synthetic_capture_buffer(frames: usize, channels: usize) -> Vec<f32> {
+    let mut out = Vec::with_capacity(frames * channels);
+    for n in 0..frames {
+        let s = 0.5 * (2.0 * PI * 440.0 * (n as f32) / 48_000.0).sin();
+        for _ in 0..channels {
+            out.push(s);
+        }
+    }
+    out
+}
+
+/// One Opus-frame-sized synthetic PCM buffer (960 samples mono).
+pub fn synthetic_opus_frame() -> Vec<f32> {
+    synthetic_capture_buffer(FRAME_SAMPLES, 1)
+}
+
+/// Synthetic encoded Opus bytes for decode benches. Built by
+/// encoding `synthetic_opus_frame()` with a one-shot encoder.
+pub fn synthetic_opus_bytes() -> Vec<u8> {
+    use audiopus::coder::Encoder;
+    use audiopus::{Application, Channels, SampleRate};
+    let enc = Encoder::new(SampleRate::Hz48000, Channels::Mono, Application::Voip)
+        .expect("opus encoder init");
+    let pcm = synthetic_opus_frame();
+    let mut out = vec![0u8; 1275]; // MAX_OPUS_FRAME
+    let len = enc
+        .encode_float(&pcm, &mut out)
+        .expect("opus encode synthetic frame");
+    out.truncate(len);
+    out
+}

crates/chanora_audio/benches/opus_codec.rs

@@ -0,0 +1,53 @@
+// SDD-120 §3 items 3-4 — Opus encode/decode latency benches.
+//
+// Both benches measure the codec-level call directly (audiopus
+// Encoder::encode_float / Decoder::decode_float) and not the
+// composite tsclientlib AudioHandler::fill_buffer call. Rationale
+// per SDD-120 §3 item 4: AudioHandler::fill_buffer conflates
+// jitter-buffer dequeue + Opus decode + PCM mix in a single call
+// and the wall-clock measurement would conflate three distinct
+// concerns. The canonical `opus_decode_latency` metric here is
+// codec-only.
+
+use audiopus::coder::{Decoder, Encoder};
+use audiopus::packet::Packet;
+use audiopus::{Application, Channels, MutSignals, SampleRate};
+use std::convert::TryFrom;
+use criterion::{black_box, criterion_group, criterion_main, Criterion};
+
+mod common;
+use common::{synthetic_opus_bytes, synthetic_opus_frame};
+
+fn bench_opus_encode_latency(c: &mut Criterion) {
+    let mut enc = Encoder::new(SampleRate::Hz48000, Channels::Mono, Application::Voip)
+        .expect("opus encoder init");
+    let pcm = synthetic_opus_frame();
+    let mut out = vec![0u8; 1275];
+
+    c.bench_function("opus_encode_latency", |b| {
+        b.iter(|| {
+            let len = enc
+                .encode_float(black_box(&pcm[..]), &mut out[..])
+                .expect("encode");
+            black_box(len);
+        });
+    });
+}
+
+fn bench_opus_decode_latency(c: &mut Criterion) {
+    let mut dec = Decoder::new(SampleRate::Hz48000, Channels::Mono).expect("opus decoder init");
+    let bytes = synthetic_opus_bytes();
+    let mut pcm_out = vec![0.0f32; 960];
+
+    c.bench_function("opus_decode_latency", |b| {
+        b.iter(|| {
+            let input = Packet::try_from(black_box(&bytes[..])).expect("packet");
+            let output = MutSignals::try_from(&mut pcm_out[..]).expect("signals");
+            let n = dec.decode_float(Some(input), output, false).expect("decode");
+            black_box(n);
+        });
+    });
+}
+
+criterion_group!(opus_codec, bench_opus_encode_latency, bench_opus_decode_latency);
+criterion_main!(opus_codec);

crates/chanora_audio/benches/realtime_capture.rs

@@ -0,0 +1,118 @@
+// SDD-120 §3 items 1-2 — realtime capture bench harness.
+//
+// - `bench_capture_alloc_count`: dhat-backed heap-allocation count
+//   across 1000 post-warmup `CaptureState::ingest` calls. Realizes
+//   the SRS-219 clause-a zero-allocation invariant. Local-developer
+//   surface additionally asserts that the post-warmup count is 0
+//   so a regression hard-fails locally; the CI advisory comparator
+//   in `compare_baseline.rs` carries the same `tolerance = 0` rule
+//   independently.
+// - `bench_capture_callback_wall_clock`: criterion default-warmup
+//   wall-clock bench of `ingest` on the same synthetic buffer.
+//
+// dhat is invasive — it replaces the global allocator for the
+// whole bench binary, but only this bench binary; production
+// builds and other benches are unaffected per Cargo's per-bench
+// compilation model.
+
+#[global_allocator]
+static ALLOC: dhat::Alloc = dhat::Alloc;
+
+use chanora_audio::bench_seam::CaptureBenchHandle;
+use criterion::{black_box, criterion_group, criterion_main, Criterion};
+
+mod common;
+use common::{synthetic_capture_buffer, FRAME_SAMPLES};
+
+fn bench_capture_alloc_count(c: &mut Criterion) {
+    // Build the dhat profiler in test mode so it is process-local
+    // and does not write a JSON heap-dump file. Held for the
+    // duration of this bench function.
+    let _profiler = dhat::Profiler::builder().testing().build();
+
+    let mut handle = CaptureBenchHandle::new(48_000, 1);
+    let buf = synthetic_capture_buffer(FRAME_SAMPLES, 1);
+
+    // 100-call warm-up to prime first-call allocations (ring
+    // growth, opus encoder lazy state, mono_scratch / pcm_accum
+    // capacity). SDD-120 §3 item 1.
+    for _ in 0..100 {
+        handle.ingest_f32(&buf);
+    }
+
+    let stats_warm = dhat::HeapStats::get();
+    let blocks_warm = stats_warm.total_blocks;
+
+    // 1000 post-warmup calls — measurement window.
+    for _ in 0..1000 {
+        handle.ingest_f32(&buf);
+    }
+
+    let stats_final = dhat::HeapStats::get();
+    let blocks_final = stats_final.total_blocks;
+    let delta = blocks_final - blocks_warm;
+
+    // Local-developer surface: hard-fail on any regression.
+    // The CI advisory comparator carries the same rule with a
+    // markdown 🔴 marker on regression instead of a panic.
+    assert_eq!(
+        delta, 0,
+        "post-warmup heap allocation regression: {} blocks (SRS-219 clause a)",
+        delta
+    );
+
+    // Register the metric value with criterion so it appears in
+    // `target/criterion/.../estimates.json` for the §5 emitter to
+    // pick up. We bench a no-op closure here because the actual
+    // measurement is the delta computed above; criterion's
+    // function-time-mean is uninteresting for an alloc-count
+    // metric. The §5 emitter reads the `capture_alloc_count`
+    // metric value out of band via a sidecar file written below.
+    c.bench_function("capture_alloc_count", |b| {
+        b.iter(|| {
+            black_box(delta);
+        });
+    });
+
+    // Sidecar file for §5 emit_baseline: criterion's own
+    // estimates.json carries the no-op closure timing, NOT the
+    // alloc count, so we write the canonical alloc-count value
+    // here and the emitter reads it directly.
+    if let Ok(dir) = std::env::var("CARGO_TARGET_DIR")
+        .map(std::path::PathBuf::from)
+        .or_else(|_| {
+            std::env::current_dir().map(|d| d.join("target"))
+        })
+    {
+        let path = dir.join("criterion").join("capture_alloc_count.sidecar");
+        if let Some(parent) = path.parent() {
+            let _ = std::fs::create_dir_all(parent);
+        }
+        let _ = std::fs::write(&path, format!("{}", delta));
+    }
+}
+
+fn bench_capture_callback_wall_clock(c: &mut Criterion) {
+    let mut handle = CaptureBenchHandle::new(48_000, 1);
+    let buf = synthetic_capture_buffer(FRAME_SAMPLES, 1);
+
+    // Pre-warm so first-call allocations do not skew the
+    // measurement window (criterion's default warmup is 3 s which
+    // is more than enough; this loop is belt-and-braces).
+    for _ in 0..100 {
+        handle.ingest_f32(&buf);
+    }
+
+    c.bench_function("capture_callback_wall_clock", |b| {
+        b.iter(|| {
+            handle.ingest_f32(black_box(&buf));
+        });
+    });
+}
+
+criterion_group!(
+    realtime_capture,
+    bench_capture_alloc_count,
+    bench_capture_callback_wall_clock
+);
+criterion_main!(realtime_capture);

crates/chanora_audio/benches/resampler.rs

@@ -0,0 +1,43 @@
+// SDD-120 §3 item 5 — resampler throughput bench.
+//
+// The chanora_audio engine uses a hand-rolled linear resampler
+// inside CaptureState (see engine.rs `resample_into_accum`); there
+// is no rubato dependency. The bench drives the same code path
+// via the §3 bench seam by instantiating CaptureBenchHandle at
+// different `in_sample_rate` values (44_100, 16_000, 48_000) and
+// feeding a 1-second buffer per iteration. Throughput is reported
+// as samples/sec via criterion's `Throughput::Elements`.
+
+use chanora_audio::bench_seam::CaptureBenchHandle;
+use criterion::{black_box, criterion_group, criterion_main, Criterion, Throughput};
+
+mod common;
+use common::synthetic_capture_buffer;
+
+fn bench_resampler_throughput(c: &mut Criterion) {
+    let mut group = c.benchmark_group("resampler_throughput");
+
+    for (label, in_rate, frames) in [
+        ("44100_to_48000", 44_100u32, 44_100usize),
+        ("16000_to_48000", 16_000u32, 16_000usize),
+        ("48000_passthrough", 48_000u32, 48_000usize),
+    ] {
+        let buf = synthetic_capture_buffer(frames, 1);
+        let mut handle = CaptureBenchHandle::new(in_rate, 1);
+        // Pre-warm so the first allocation does not dominate.
+        for _ in 0..4 {
+            handle.ingest_f32(&buf);
+        }
+        group.throughput(Throughput::Elements(frames as u64));
+        group.bench_function(label, |b| {
+            b.iter(|| {
+                handle.ingest_f32(black_box(&buf));
+            });
+        });
+    }
+
+    group.finish();
+}
+
+criterion_group!(resampler, bench_resampler_throughput);
+criterion_main!(resampler);

crates/chanora_audio/examples/compare_baseline.rs

@@ -0,0 +1,240 @@
+// SDD-120 §8 — PR-vs-baseline comparator binary.
+//
+// Reads `current.json` (from §5 emit_baseline) and `baseline.json`
+// (extracted from the SAD-089 path at the merge-base by the §6
+// workflow) and emits a markdown report applying:
+//
+//   - Zero-tolerance metrics (SRS-219 clause a — capture_alloc_count):
+//       🔴 if c != 0 else 🟢. Yellow does not apply.
+//   - Otherwise (t > 0):
+//       delta_pct = (c - b) / b   (or 0 if b == 0)
+//       🔴 if delta_pct > t
+//       🟡 if 0.5*t < delta_pct ≤ t
+//       🟢 otherwise (including improvements, delta_pct < 0)
+//
+// Always exits 0 — regression detection is rendered as a 🔴 marker
+// inside the markdown comment, NOT as a non-zero exit code
+// (SRS-218 clause 4).
+//
+// CLI:
+//   cargo run --bin compare_baseline -- \
+//     --current ./current.json \
+//     --baseline ./baseline.json \
+//     --output ./report.md
+
+use std::collections::HashMap;
+use std::fs;
+use std::path::PathBuf;
+use std::process::ExitCode;
+
+use serde_json::Value;
+
+struct Args {
+    current: PathBuf,
+    baseline: PathBuf,
+    output: PathBuf,
+}
+
+fn parse_args() -> Args {
+    let mut current = PathBuf::from("current.json");
+    let mut baseline = PathBuf::from("baseline.json");
+    let mut output = PathBuf::from("report.md");
+    let mut it = std::env::args().skip(1);
+    while let Some(a) = it.next() {
+        match a.as_str() {
+            "--current" => current = PathBuf::from(it.next().unwrap_or_default()),
+            "--baseline" => baseline = PathBuf::from(it.next().unwrap_or_default()),
+            "--output" => output = PathBuf::from(it.next().unwrap_or_default()),
+            _ => {}
+        }
+    }
+    Args {
+        current,
+        baseline,
+        output,
+    }
+}
+
+fn read_metrics(path: &PathBuf) -> (Option<Value>, HashMap<String, MetricRow>) {
+    let mut out = HashMap::new();
+    let text = match fs::read_to_string(path) {
+        Ok(t) => t,
+        Err(_) => return (None, out),
+    };
+    if text.trim().is_empty() || text.trim() == "{}" {
+        return (None, out);
+    }
+    let v: Value = match serde_json::from_str(&text) {
+        Ok(v) => v,
+        Err(_) => return (None, out),
+    };
+    let metrics = v.get("metrics").and_then(|m| m.as_array()).cloned();
+    if let Some(arr) = metrics {
+        for m in arr {
+            let name = m
+                .get("metric")
+                .and_then(|s| s.as_str())
+                .unwrap_or("")
+                .to_string();
+            let unit = m
+                .get("unit")
+                .and_then(|s| s.as_str())
+                .unwrap_or("")
+                .to_string();
+            let value = m.get("value").and_then(|n| n.as_f64());
+            let tolerance = m
+                .get("tolerance_pct")
+                .and_then(|n| n.as_f64())
+                .unwrap_or(0.0);
+            if !name.is_empty() {
+                out.insert(
+                    name.clone(),
+                    MetricRow {
+                        metric: name,
+                        unit,
+                        value,
+                        tolerance_pct: tolerance,
+                    },
+                );
+            }
+        }
+    }
+    (Some(v), out)
+}
+
+#[derive(Clone)]
+struct MetricRow {
+    metric: String,
+    unit: String,
+    value: Option<f64>,
+    tolerance_pct: f64,
+}
+
+fn fmt_value(v: Option<f64>) -> String {
+    match v {
+        Some(x) if x.is_finite() => {
+            if x.abs() >= 1_000_000.0 {
+                format!("{:.3e}", x)
+            } else if x.abs() >= 1.0 {
+                format!("{:.3}", x)
+            } else {
+                format!("{:.6}", x)
+            }
+        }
+        _ => "n/a".to_string(),
+    }
+}
+
+fn marker(b: Option<f64>, c: Option<f64>, t: f64) -> (String, String) {
+    // Returns (marker, delta_str)
+    let (b, c) = match (b, c) {
+        (Some(b), Some(c)) => (b, c),
+        _ => return ("⚪".to_string(), "n/a".to_string()),
+    };
+    if t == 0.0 {
+        // Zero-tolerance metric (SRS-219 clause a).
+        if c != 0.0 {
+            return ("🔴".to_string(), format!("{:+}", c as i64));
+        } else {
+            return ("🟢".to_string(), "+0".to_string());
+        }
+    }
+    let delta_pct = if b > 0.0 { (c - b) / b } else { 0.0 };
+    let delta_str = format!("{:+.2}%", delta_pct * 100.0);
+    let m = if delta_pct > t {
+        "🔴"
+    } else if delta_pct > 0.5 * t {
+        "🟡"
+    } else {
+        "🟢"
+    };
+    (m.to_string(), delta_str)
+}
+
+fn main() -> ExitCode {
+    let args = parse_args();
+    let (cur_doc, cur) = read_metrics(&args.current);
+    let (base_doc, base) = read_metrics(&args.baseline);
+
+    let mut md = String::new();
+    md.push_str("<!-- chanora-bench-advisory -->\n");
+    md.push_str("### Chanora realtime-audio benchmark advisory (SDD-120)\n\n");
+
+    if cur_doc.is_none() {
+        md.push_str("_No `current.json` found — bench harness did not produce results._\n");
+        fs::write(&args.output, &md).expect("write report");
+        return ExitCode::SUCCESS;
+    }
+
+    if base.is_empty() {
+        md.push_str(
+            "_Baseline not yet established at merge-base; first dispatch of \
+            `bench-baseline-update.yml` on the default branch will establish \
+            it. No red markers emitted on this first run._\n\n",
+        );
+        md.push_str("| Metric | Unit | Current |\n");
+        md.push_str("|---|---|---|\n");
+        let mut keys: Vec<&String> = cur.keys().collect();
+        keys.sort();
+        for k in keys {
+            let row = &cur[k];
+            md.push_str(&format!(
+                "| `{}` | {} | {} |\n",
+                row.metric,
+                row.unit,
+                fmt_value(row.value)
+            ));
+        }
+        fs::write(&args.output, &md).expect("write report");
+        return ExitCode::SUCCESS;
+    }
+
+    if let Some(d) = base_doc.as_ref() {
+        if let Some(sha) = d.get("git_sha").and_then(|s| s.as_str()) {
+            md.push_str(&format!("Baseline `git_sha`: `{}`\n\n", sha));
+        }
+    }
+
+    md.push_str("| Metric | Unit | Baseline | Current | Δ | Tolerance | Status |\n");
+    md.push_str("|---|---|---|---|---|---|---|\n");
+
+    // Iterate over the union of metric names, sorted.
+    let mut all: Vec<String> = cur.keys().chain(base.keys()).cloned().collect();
+    all.sort();
+    all.dedup();
+    for name in all {
+        let c = cur.get(&name);
+        let b = base.get(&name);
+        let unit = c
+            .map(|r| r.unit.clone())
+            .or_else(|| b.map(|r| r.unit.clone()))
+            .unwrap_or_default();
+        let tol = c
+            .map(|r| r.tolerance_pct)
+            .or_else(|| b.map(|r| r.tolerance_pct))
+            .unwrap_or(0.0);
+        let (m, delta) = marker(b.and_then(|r| r.value), c.and_then(|r| r.value), tol);
+        md.push_str(&format!(
+            "| `{}` | {} | {} | {} | {} | {} | {} |\n",
+            name,
+            unit,
+            fmt_value(b.and_then(|r| r.value)),
+            fmt_value(c.and_then(|r| r.value)),
+            delta,
+            if tol == 0.0 {
+                "0 (zero-tolerance)".to_string()
+            } else {
+                format!("{:.1}%", tol * 100.0)
+            },
+            m,
+        ));
+    }
+
+    md.push_str(
+        "\n_Advisory only — this workflow never fails a check on regression \
+        (SRS-218 clause 4)._\n",
+    );
+
+    fs::write(&args.output, &md).expect("write report");
+    ExitCode::SUCCESS
+}

crates/chanora_audio/examples/emit_baseline.rs

@@ -0,0 +1,207 @@
+// SDD-120 §5 — JSON post-processor binary.
+//
+// Reads criterion's per-bench `target/criterion/<group>/<bench>/estimates.json`
+// outputs, plus the `capture_alloc_count.sidecar` value written by
+// `realtime_capture.rs`, and projects them into the SRS-217 schema:
+//   {
+//     "host":       "x86_64-unknown-linux-gnu",
+//     "toolchain":  "<rustc -V>",
+//     "git_sha":    "<HEAD>",
+//     "timestamp":  "<RFC3339 UTC>",
+//     "metrics": [
+//       { "metric": "<name>", "value": <f64>, "unit": "<u>",
+//         "tolerance_pct": <f64>, ... },
+//       ...
+//     ]
+//   }
+//
+// Writes the document to `./current.json`.
+//
+// Run as: `cargo run --bin emit_baseline -p chanora_audio`.
+
+use std::env;
+use std::fs;
+use std::path::{Path, PathBuf};
+use std::process::Command;
+use std::time::{SystemTime, UNIX_EPOCH};
+
+use serde_json::{json, Value};
+
+/// Per-metric SRS-219 tolerance entries. Zero-tolerance metrics
+/// per SRS-219 clause a use 0.0 here; the comparator collapses
+/// them to 🔴/🟢 only.
+fn metric_table() -> Vec<(&'static str, &'static str, f64)> {
+    // (metric_name, unit, tolerance_pct)
+    vec![
+        ("capture_alloc_count", "blocks", 0.0),
+        ("capture_callback_wall_clock", "ns", 0.10),
+        ("opus_encode_latency", "ns", 0.10),
+        ("opus_decode_latency", "ns", 0.10),
+        ("resampler_44100_to_48000", "samples_per_sec", 0.10),
+        ("resampler_16000_to_48000", "samples_per_sec", 0.10),
+        ("resampler_48000_passthrough", "samples_per_sec", 0.10),
+    ]
+}
+
+fn target_dir() -> PathBuf {
+    env::var("CARGO_TARGET_DIR")
+        .map(PathBuf::from)
+        .unwrap_or_else(|_| PathBuf::from("target"))
+}
+
+/// Read criterion `estimates.json` for a given bench function
+/// name (criterion writes one per non-grouped bench under
+/// `target/criterion/<bench>/new/estimates.json`).
+fn read_estimate_ns(name: &str) -> Option<f64> {
+    let path = target_dir()
+        .join("criterion")
+        .join(name)
+        .join("new")
+        .join("estimates.json");
+    let text = fs::read_to_string(&path).ok()?;
+    let v: Value = serde_json::from_str(&text).ok()?;
+    // criterion estimates.json has `mean.point_estimate` (in ns).
+    v.get("mean")
+        .and_then(|m| m.get("point_estimate"))
+        .and_then(|p| p.as_f64())
+}
+
+/// Read criterion `estimates.json` for a sub-bench inside a group
+/// (criterion writes group sub-benches under
+/// `target/criterion/<group>/<sub>/new/estimates.json`).
+fn read_estimate_group_ns(group: &str, sub: &str) -> Option<f64> {
+    let path = target_dir()
+        .join("criterion")
+        .join(group)
+        .join(sub)
+        .join("new")
+        .join("estimates.json");
+    let text = fs::read_to_string(&path).ok()?;
+    let v: Value = serde_json::from_str(&text).ok()?;
+    v.get("mean")
+        .and_then(|m| m.get("point_estimate"))
+        .and_then(|p| p.as_f64())
+}
+
+/// Resampler reports throughput; convert ns-per-iter to samples
+/// per second using the per-iter input length (1s @ rate).
+fn ns_to_throughput(ns_per_iter: f64, samples_per_iter: f64) -> f64 {
+    if ns_per_iter <= 0.0 {
+        return 0.0;
+    }
+    samples_per_iter * 1_000_000_000.0 / ns_per_iter
+}
+
+fn read_alloc_sidecar() -> Option<f64> {
+    let path = target_dir()
+        .join("criterion")
+        .join("capture_alloc_count.sidecar");
+    let s = fs::read_to_string(&path).ok()?;
+    s.trim().parse::<f64>().ok()
+}
+
+fn rustc_version() -> String {
+    Command::new("rustc")
+        .arg("-V")
+        .output()
+        .ok()
+        .and_then(|o| {
+            if o.status.success() {
+                Some(String::from_utf8_lossy(&o.stdout).trim().to_string())
+            } else {
+                None
+            }
+        })
+        .unwrap_or_else(|| "unknown".to_string())
+}
+
+fn git_sha() -> String {
+    Command::new("git")
+        .args(["rev-parse", "HEAD"])
+        .output()
+        .ok()
+        .and_then(|o| {
+            if o.status.success() {
+                Some(String::from_utf8_lossy(&o.stdout).trim().to_string())
+            } else {
+                None
+            }
+        })
+        .unwrap_or_else(|| "unknown".to_string())
+}
+
+fn rfc3339_now() -> String {
+    let secs = SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .map(|d| d.as_secs())
+        .unwrap_or(0);
+    // Minimal RFC3339-style UTC encoder; avoids pulling chrono.
+    // Algorithm: civil-from-days (Howard Hinnant).
+    let z = secs / 86_400;
+    let day_secs = secs % 86_400;
+    let hh = day_secs / 3600;
+    let mm = (day_secs % 3600) / 60;
+    let ss = day_secs % 60;
+    let z_shift = z as i64 + 719_468;
+    let era = z_shift.div_euclid(146_097);
+    let doe = z_shift.rem_euclid(146_097) as u64;
+    let yoe = (doe - doe / 1460 + doe / 36_524 - doe / 146_096) / 365;
+    let y = yoe as i64 + era * 400;
+    let doy = doe - (365 * yoe + yoe / 4 - yoe / 100);
+    let mp = (5 * doy + 2) / 153;
+    let d = doy - (153 * mp + 2) / 5 + 1;
+    let m = if mp < 10 { mp + 3 } else { mp - 9 };
+    let year = if m <= 2 { y + 1 } else { y };
+    format!(
+        "{:04}-{:02}-{:02}T{:02}:{:02}:{:02}Z",
+        year, m, d, hh, mm, ss
+    )
+}
+
+fn main() {
+    let mut metrics: Vec<Value> = Vec::new();
+    for (name, unit, tol) in metric_table() {
+        let value = match name {
+            "capture_alloc_count" => read_alloc_sidecar(),
+            "capture_callback_wall_clock" => read_estimate_ns(name),
+            "opus_encode_latency" => read_estimate_ns(name),
+            "opus_decode_latency" => read_estimate_ns(name),
+            "resampler_44100_to_48000" => read_estimate_group_ns(
+                "resampler_throughput",
+                "44100_to_48000",
+            )
+            .map(|ns| ns_to_throughput(ns, 44_100.0)),
+            "resampler_16000_to_48000" => read_estimate_group_ns(
+                "resampler_throughput",
+                "16000_to_48000",
+            )
+            .map(|ns| ns_to_throughput(ns, 16_000.0)),
+            "resampler_48000_passthrough" => read_estimate_group_ns(
+                "resampler_throughput",
+                "48000_passthrough",
+            )
+            .map(|ns| ns_to_throughput(ns, 48_000.0)),
+            _ => None,
+        };
+        let v = value.unwrap_or(f64::NAN);
+        metrics.push(json!({
+            "metric": name,
+            "value": if v.is_finite() { Value::from(v) } else { Value::Null },
+            "unit": unit,
+            "tolerance_pct": tol,
+        }));
+    }
+
+    let doc = json!({
+        "host": "x86_64-unknown-linux-gnu",
+        "toolchain": rustc_version(),
+        "git_sha": git_sha(),
+        "timestamp": rfc3339_now(),
+        "metrics": metrics,
+    });
+
+    let out_path = Path::new("current.json");
+    fs::write(out_path, serde_json::to_string_pretty(&doc).unwrap())
+        .expect("write current.json");
+    eprintln!("emit_baseline: wrote {}", out_path.display());
+}

crates/chanora_audio/src/engine.rs

@@ -1797,3 +1797,86 @@ pub fn android_set_audio_mode(mode: i32) -> Result<(), AudioModeError> {
         Ok(())
     })
 }
+
+// ---------------------------------------------------------------------------
+// SDD-120 §3 bench seam.
+//
+// Exposes a minimal factory for `CaptureState` plus a thin `ingest_f32`
+// shim so the criterion bench harness in `crates/chanora_audio/benches/`
+// can drive the same realtime capture code path the production cpal
+// callback uses, without re-implementing CaptureState in the bench file.
+// Marked `#[doc(hidden)]` so the public API surface is unaffected; this
+// is not a supported external API. Only compiled on non-iOS targets
+// because `CaptureState` itself is gated on `cfg(not(target_os = "ios"))`.
+// ---------------------------------------------------------------------------
+#[cfg(not(target_os = "ios"))]
+#[doc(hidden)]
+pub mod bench_seam {
+    use super::{
+        AtomicBool, AtomicU32, Arc, CaptureState, OpusApp, OpusChannels, OpusEncoder,
+        OpusSampleRate, OutPacket,
+    };
+    use tokio::sync::mpsc;
+
+    /// Opaque handle wrapping a CaptureState plus the dummy mpsc
+    /// receiver that prevents the channel sender from erroring out
+    /// when the bench drives `ingest`. The receiver is held inside
+    /// the handle so it lives for the bench's lifetime.
+    pub struct CaptureBenchHandle {
+        state: CaptureState,
+        // Keep the receiver alive so sends from CaptureState::encode_and_send
+        // do not fail; the bench discards what would be transmitted.
+        _rx: mpsc::Receiver<OutPacket>,
+        transmit_active: Arc<AtomicBool>,
+    }
+
+    impl CaptureBenchHandle {
+        /// Construct a CaptureState wired to a private mpsc + a
+        /// pre-asserted transmit-active flag so `ingest` exercises
+        /// the full down-mix → resample → encode → send pipeline.
+        ///
+        /// `in_sample_rate` selects the input rate (48000 for the
+        /// passthrough path, 44100 / 16000 to exercise the linear
+        /// resampler). `in_channels` selects the channel layout
+        /// (typically 1 or 2).
+        pub fn new(in_sample_rate: u32, in_channels: usize) -> Self {
+            let encoder = OpusEncoder::new(
+                OpusSampleRate::Hz48000,
+                OpusChannels::Mono,
+                OpusApp::Voip,
+            )
+            .expect("opus encoder init");
+            let (tx, rx) = mpsc::channel::<OutPacket>(64);
+            let transmit_active = Arc::new(AtomicBool::new(true));
+            let frames_sent = Arc::new(AtomicU32::new(0));
+            let state = CaptureState::new(
+                encoder,
+                in_sample_rate,
+                in_channels,
+                1.0,
+                tx,
+                transmit_active.clone(),
+                frames_sent,
+            );
+            Self {
+                state,
+                _rx: rx,
+                transmit_active,
+            }
+        }
+
+        /// Drive one cpal-callback-equivalent buffer through the
+        /// realtime capture pipeline.
+        #[inline]
+        pub fn ingest_f32(&mut self, buf: &[f32]) {
+            self.state.ingest(buf);
+        }
+
+        /// Set the PTT gate. Defaults to true (bench measures the
+        /// transmitting path).
+        pub fn set_transmit_active(&self, active: bool) {
+            self.transmit_active
+                .store(active, std::sync::atomic::Ordering::Relaxed);
+        }
+    }
+}

crates/chanora_audio/src/lib.rs

@@ -47,6 +47,14 @@ mod ios_voice_unit;
 pub mod android_voice_unit;
 
 pub use engine::{AudioEngine, AudioEngineConfig};
+
+// SDD-120 §3 bench seam — `#[doc(hidden)]` re-export so the criterion
+// bench harness under `crates/chanora_audio/benches/` can construct a
+// CaptureState and drive `ingest` without re-implementing the engine.
+// Not part of the supported public API.
+#[cfg(not(target_os = "ios"))]
+#[doc(hidden)]
+pub use engine::bench_seam;
 pub use ptt::{AudioTransmitGate, MissedKeyUpWatchdog, PttBackendDescriptor, PttCapabilityLevel};
 pub use ptt_backends::{
     select as select_ptt_backend, DesktopPttBackend, FocusedPttBackend, PttBackendError,