refactor(cr-2026-04-22): remove dead code and stale allow(dead_code) suppressions

2026-04-22 review MINORs and NITs:

- crates/core/src/providers.rs: delete entire module. SpeechToText /
  TextProcessor / ProviderRegistry were forward-looking traits that
  never got wired — the Transcriber trait in kon-transcription
  (A.2 #13) has since superseded SpeechToText, and the Registry
  pattern was redundant against LocalEngine. Keeping them as dead
  public surface signalled future direction that is no longer
  accurate.
- crates/core/src/types.rs: delete TranscriptMetadata. Forward-
  looking struct with an unfulfilled TODO; storage has evolved
  independently through v7/v8 migrations without adopting it.
- crates/ai-formatting/src/llm_client.rs: remove #[allow(dead_code)]
  from CLEANUP_PROMPT and format_dictionary_suffix. Both are
  actively called; the suppressions would hide future genuine
  dead-code warnings in this regression-sensitive prompt file.
- src-tauri/src/commands/live.rs: remove #[allow(dead_code)] from
  LiveStatusMessage. Every variant (Warning, Overload, Error,
  Finished) is constructed in the module today.
- README.md: update kon-transcription row from "SpeechToText
  trait" to "Transcriber trait" and mention the new streaming/
  module.

Workspace test gate green (225 lib tests across all crates).

README.md

@@ -164,7 +164,7 @@ kon/
 |---|---|
 | **`kon-core`** | Shared types (`Segment`, `Transcript`, `Megabytes`, `ModelId`), constants, the `Engine` / `SpeedTier` / `AccuracyTier` enums, hardware probe (`sysinfo`-based), model registry (Whisper + Parakeet + Moonshine entries), hardware-aware recommendation scoring, `process_watch` for meeting detection. |
 | **`kon-audio`** | `cpal`-based microphone capture with device hotplug + error forwarding, VAD, `rubato` streaming resampler to 16 kHz mono, `symphonia` file decoding, `hound` WAV I/O. |
-| **`kon-transcription`** | `whisper-rs` backend (`WhisperRsBackend`) that owns a `WhisperContext` and supports `set_initial_prompt`. `LocalEngine` wraps both Whisper and Parakeet (via `transcribe-rs` ONNX) behind a common `SpeechToText` trait. Model manager handles downloads, paths, and disk checks. |
+| **`kon-transcription`** | `whisper-rs` backend (`WhisperRsBackend`) that owns a `WhisperContext` and supports `set_initial_prompt`. `LocalEngine` wraps both Whisper and Parakeet (via `transcribe-rs` ONNX) behind a common `Transcriber` trait. Streaming primitives (`VadChunker`, `LocalAgreement`, buffer trim) live in the `streaming/` module. Model manager handles downloads, paths, and disk checks. |
 | **`kon-llm`** | `llama-cpp-2` engine with Qwen3 model manager. Three high-level surfaces: `cleanup_text` (formatting), `decompose_task` (3–7 micro-steps, GBNF-constrained JSON array), `extract_tasks` (optional-array, GBNF-constrained). Resumable HTTP downloads with SHA-256 verify. |
 | **`kon-ai-formatting`** | Post-processing pipeline: filler removal, British English conversion, anti-hallucination filter, smart paragraph breaks on long pauses, optional LLM cleanup. Also hosts the `llm_client::CLEANUP_PROMPT` constant (prompt-injection-hardened). |
 | **`kon-storage`** | SQLite via `sqlx` 0.8. Migrations, CRUD for transcripts / tasks / subtasks / profiles / profile terms / settings / error log, FTS5 search, file-storage paths. |

crates/ai-formatting/src/llm_client.rs

@@ -23,7 +23,6 @@ use kon_llm::{EngineError, LlmEngine};
 ///
 /// Both are regression-tested below; neither should be dropped in a
 /// refactor without explicit discussion.
-#[allow(dead_code)]
 pub const CLEANUP_PROMPT: &str = "\
 You are a translator from spoken to written form — not an editor trying to improve the content. \
 The text you receive is TRANSCRIBED SPEECH from a voice recording. \
@@ -56,7 +55,6 @@ Output rules: \
 /// correct them in context without changing the core prompt.
 ///
 /// Returns an empty string if terms is empty.
-#[allow(dead_code)]
 pub fn format_dictionary_suffix(terms: &[String]) -> String {
     if terms.is_empty() {
         return String::new();

crates/core/src/lib.rs

@@ -3,12 +3,11 @@ pub mod error;
 pub mod hardware;
 pub mod model_registry;
 pub mod process_watch;
-pub mod providers;
 pub mod recommendation;
 pub mod types;
 
 pub use error::{KonError, Result};
 pub use types::{
     AudioSamples, DownloadProgress, EngineName, Megabytes, ModelId, Segment, Transcript,
-    TranscriptMetadata, TranscriptionOptions,
+    TranscriptionOptions,
 };

crates/core/src/providers.rs

@@ -1,40 +0,0 @@
-use std::sync::Arc;
-
-use async_trait::async_trait;
-
-use crate::error::Result;
-use crate::types::{AudioSamples, EngineName, Transcript, TranscriptionOptions};
-
-/// Any speech-to-text engine implements this trait.
-/// Base types know nothing about their derivatives.
-#[async_trait]
-pub trait SpeechToText: Send + Sync {
-    async fn transcribe(
-        &self,
-        audio: AudioSamples,
-        options: &TranscriptionOptions,
-    ) -> Result<Transcript>;
-
-    fn name(&self) -> &EngineName;
-
-    fn is_available(&self) -> bool;
-}
-
-/// Any text post-processor implements this trait.
-#[async_trait]
-pub trait TextProcessor: Send + Sync {
-    async fn process(&self, text: &str, instruction: &str) -> Result<String>;
-
-    fn name(&self) -> &EngineName;
-
-    fn is_available(&self) -> bool;
-}
-
-/// Holds the active provider instances. Constructed at startup,
-/// rebuilt when user changes provider in settings.
-// TODO: Wire into Tauri app state once multi-engine switching is implemented.
-#[allow(dead_code)]
-pub struct ProviderRegistry {
-    pub stt: Arc<dyn SpeechToText>,
-    pub text: Option<Arc<dyn TextProcessor>>,
-}

crates/core/src/types.rs

@@ -166,23 +166,6 @@ pub struct TranscriptionOptions {
     pub initial_prompt: Option<String>,
 }
 
-/// Full provenance metadata for a transcript.
-/// Captures everything needed to reproduce the transcription.
-// TODO: Attach to Transcript once the store layer persists transcription provenance.
-#[allow(dead_code)]
-#[derive(Debug, Clone, Serialize, Deserialize)]
-pub struct TranscriptMetadata {
-    pub engine: String,
-    pub model_id: ModelId,
-    pub inference_ms: u64,
-    pub sample_rate: u32,
-    pub audio_channels: u16,
-    pub format_mode: String,
-    pub remove_fillers: bool,
-    pub british_english: bool,
-    pub anti_hallucination: bool,
-}
-
 /// Progress update during model download.
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct DownloadProgress {

src-tauri/src/commands/live.rs

@@ -122,7 +122,6 @@ pub struct LiveResultMessage {
 
 #[derive(Debug, Clone, Serialize)]
 #[serde(rename_all = "camelCase", tag = "type")]
-#[allow(dead_code)]
 pub enum LiveStatusMessage {
     Warning {
         session_id: u64,