agent: engine slop pass — DSP, typed errors, regex parsing, tracing, audit fixes

External code review on 2026-05-12 rated the codebase 4/10 across audio DSP, error typing, JS injection, env-var safety, ALSA parsing, and async logging. This commit lands the prognosis-level fixes plus three audit follow-ups.

Audio/DSP:
- StreamingResampler/rubato confirmed in the live capture path
- regression test at 12 kHz (rms < 0.01, ~40 dB) catches naive decimation
- near-Nyquist test at 9 kHz (rms < 0.05, ~26 dB) exercises transition band

Core errors:
- Other(String) removed; ProviderNotRegistered introduced
- Io variant restructured as struct with kind/message/raw_os_error
- FileNotFound display quotes paths
- Configuration variant removed (unused)

Core types:
- ModelId, EngineName backed by Cow<'static, str>; const borrowed ctor
- Megabytes::from_gb takes u64 (was f64)
- AudioSamples::sample_rate is NonZeroU32; zero-rate defensive branch removed

Capture:
- /proc/asound/cards parsing rewritten as anchored regex (OnceLock)
- regression test covers product names with embedded colons
- monitor_pattern_detection test restored alongside the regex test
- DEAD_SILENCE_FLOOR promoted to module-level with rationale
- DEVICE_VALIDATION_MS, SILENCE_RMS_FLOOR documented with field-observation rationale
- RMS validation loop made idiomatic
- eprintln! migrated to tracing with structured fields and targets

Tauri startup:
- unsafe std::env::set_var removed; ensure_x11_on_wayland renamed to warn_if_x11_env_unset_on_wayland (launcher/wrapper owns env-var contract)
- DB init + log prune + preferences load collapsed to one block_on
- build_preferences_script rewrites JS injection from JSON.parse string to direct object literal plus malformed-JSON guard and unit tests
- WebKitGTK microphone auto-grant logs warning at startup
- tracing subscriber initialised at top of run() (warn,magnotia=info,... on stderr; honors RUST_LOG); previously eprintln→tracing migration was silent because no subscriber existed

Filename counter:
- RECORDING_COUNTER uses SeqCst

Tests: cargo test --workspace --lib green (322 passed, 0 failed across 10 crates).

Three independent audits (original cleanup → Wren → fresh Codex subagent) concur on no critical findings.

Deferred to docs/superpowers/plans/2026-05-12-engine-slop-residuals.md: storage-layer typed errors, remaining eprintln→tracing sweep, capture actor-model refactor, property-based DSP testing, frontend/backend error boundary cleanup.

Cargo.lock

@@ -2705,9 +2705,9 @@ checksum = "92daf443525c4cce67b150400bc2316076100ce0b3686209eb8cf3c31612e6f0"
 
 [[package]]
 name = "llama-cpp-2"
-version = "0.1.145"
+version = "0.1.146"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2e82b8c7a1c1a0ad97e1cc5cc28e01e9e14be73d4068e0fe9ac9d6c465001323"
+checksum = "f3b0f368c76cc0fe475e8257aeeec269e0d6569bd48b1f503efd0963fc3ee397"
 dependencies = [
  "encoding_rs",
  "enumflags2",
@@ -2719,9 +2719,9 @@ dependencies = [
 
 [[package]]
 name = "llama-cpp-sys-2"
-version = "0.1.145"
+version = "0.1.146"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9e1e5495433ca7487b9f8c7046f64e69937861d438b20f12ee3c524f35d55ad3"
+checksum = "9b291e4bc2d10c43cd8dec16d49b6104cb3cb125f596ec380a753a5db1d965dd"
 dependencies = [
  "bindgen",
  "cc",
@@ -2816,6 +2816,8 @@ dependencies = [
  "tauri-plugin-window-state",
  "tempfile",
  "tokio",
+ "tracing",
+ "tracing-subscriber",
  "uuid",
  "webkit2gtk",
 ]
@@ -2836,10 +2838,12 @@ dependencies = [
  "cpal",
  "hound",
  "magnotia-core",
+ "regex",
  "rubato",
  "serde",
  "symphonia",
  "tokio",
+ "tracing",
 ]
 
 [[package]]