Record D-WS7a: Parakeet runtime decision, engine path and CPU measurements vs Large v3 Turbo

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/Architecture.md

@@ -68,11 +68,15 @@ src/
     audio.ts               # decode + resample to 16 kHz mono Float32Array (Web Audio API)
     live.ts                # live-mode segment loop: RMS gate, LiveSegmenter, LiveTranscriber (pure, D-016)
     mic.ts                 # microphone capture: AudioWorklet chunker (Blob URL) + fallback (D-016)
-    models.ts              # model catalog: ids, sizes, dtype defaults per device, languages
+    models.ts              # model catalog: ids, family (whisper|parakeet), sizes, dtype defaults per device, languages
+    parakeet.ts            # pure Parakeet logic: ≤30 s window plan, words→chunks, vocab tokenizer, pinned URLs
     modelCache.ts          # "downloaded?" per model via Cache Storage (D-005; reused by M3 offline indicator)
     engine.ts              # engine abstraction: BrowserEngine | ServerEngine
   worker/
-    inference.worker.ts    # Transformers.js pipeline, WebNN/WebGPU/WASM selection
+    inference.worker.ts    # Transformers.js pipeline, WebNN/WebGPU/WASM selection; dispatches on catalog `family`
+    parakeetEngine.ts      # Parakeet TDT path: parakeet.js ParakeetModel on the shared onnxruntime-web (D-WS7a)
+    modelFiles.ts          # Cache-API weight download for non-Transformers.js paths (same cache, same progress msgs)
+    ortShim.ts             # re-exports onnxruntime-web/webgpu; parakeet.js's own ort import is aliased here
     protocol.ts            # typed postMessage messages (shared with UI)
   pwa/
     sw.ts                  # service worker (app-shell precache, /ort runtime cache)
@@ -217,11 +221,40 @@ environment). See `WorkBreakdown.md` for the itemized checklist.)
 - Anonymous users are never blocked from browser inference — auth only unlocks the
   server engine.
 
+### 4.1c Parakeet (English-only, desktop-only browser model — D-WS7a)
+Catalog entries carry `family?: "whisper" | "parakeet"` (absent ⇒ whisper). For
+`family: "parakeet"` the worker skips the Transformers.js pipeline:
+1. **Load:** `modelFiles.ts` fetches `vocab.txt`, the decoder_joint and the
+   encoder from the Hub (revision-pinned URLs, `lib/parakeet.ts`) into the same
+   `transformers-cache` Cache Storage cache Transformers.js uses, posting the same
+   `load-progress` messages — so badges, the storage panel, delete and
+   ModelLoadProgress work unchanged. A file is cached only once complete.
+   Devices: `parakeetDeviceAttempts` — WASM int8 unless WebGPU is chosen
+   explicitly (fp16 encoder on WebGPU + int8 decoder on WASM, needs
+   `shader-f16`); the D-025 restart rule applies.
+2. **Runtime:** `parakeetEngine.ts` builds parakeet.js's `ParakeetModel` from our
+   own sessions on `onnxruntime-web/webgpu` — the module Transformers.js imports,
+   so there is one runtime and one `/ort/` wasm. parakeet.js's `initOrt` (own ort
+   copy, CDN wasm path) is never called; `scripts/ortAlias.ts` points its import
+   at `worker/ortShim.ts` so the bundle carries one ort (`tests/workerBundle.test.ts`).
+3. **Transcribe:** audio is planned into ≤ 30 s windows cut at the quietest 100 ms
+   near each limit (`subarray` views, no copies); each window's word timestamps
+   become sentence-sized `TranscriptChunk`s with absolute times. File passes post
+   one `partial` + `transcribe-progress` per window; live passes resolve via
+   `result` like Whisper's, so `LiveTranscriber`, TranscriptView and export are
+   untouched. `language`/`task` are ignored (English only).
+4. **UI:** the picker lists it under English-only with a one-line note, hides it on
+   phones/tablets (`modelsForDevice`), and the server-engine list never includes
+   it (no faster-whisper name). With it selected, a note replaces the language/task
+   controls.
+
 ## 5. Invariants
 
 - **Privacy:** browser-engine audio and transcripts never touch the network.
 - **Anonymous-first:** every feature except the server engine works logged out.
 - **Offline-first:** app shell + previously-downloaded models must work offline.
-- **One browser inference codebase:** Transformers.js in the browser; the server
-  engine runs faster-whisper (D-013). The model catalog stays shared across both.
+- **One browser inference runtime:** onnxruntime-web, driven by Transformers.js for
+  Whisper and by parakeet.js for Parakeet (D-WS7a) — the same ort instance, never a
+  second runtime; the server engine runs faster-whisper (D-013). The model catalog
+  stays shared across both engines (browser-only entries have no faster-whisper name).
 - **Worker isolation:** inference never runs on the main thread.