Document Speaches speech layer, on-device processing limits, latency constraints

- STT/TTS move to a shared Speaches container (OpenAI-format, GPU, port
  8601 proposed); gateway becomes a thin orchestrator with pluggable
  speech backends (speaches default, embedded fallback)
- Record the on-device ceiling: WakeNet wake word, VAD, ES7210 AEC,
  optional MultiNet fixed commands; open-vocabulary STT permanently out
- Record the real latency bottleneck (Tatlock ~2 min full local flow):
  gateway must stream chat tokens and synthesize sentence-by-sentence
- Plan reply_delta + barge-in protocol additions

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

README.md

@@ -25,28 +25,28 @@ happens on this server.
 ## Architecture
 
 ```
-┌─────────────────────┐        WebSocket (PCM audio + JSON events)
-│  DeskLock device    │◄──────────────────────────────────────────┐
-│  (ESP32-P4)         │                                           │
-│                     │        ┌──────────────────────────────────┴──┐
-│  • LVGL face        │        │  DeskLock Gateway (container)        │
-│  • Touch input      │        │  on tower-of-joy                     │
-│  • Mic capture+AEC  │        │                                      │
-│  • TTS playback     │        │  • STT: faster-whisper (GPU)         │
-└─────────────────────┘        │  • TTS: Piper                        │
-                               │  • Chat: Tatlock /v1/chat/completions│
-                               └──────────────────┬───────────────────┘
-                                                  │ HTTP (LAN, :8000)
-                                       ┌──────────┴──────────┐
-                                       │  Tatlock (butler)   │
-                                       │  tatlock.schweitz.  │
-                                       │  internal           │
-                                       └─────────────────────┘
+┌──────────────────────┐  WebSocket: PCM audio + JSON events
+│  DeskLock device     │◄───────────────────────────────────┐
+│  (ESP32-P4)          │                                    │
+│  • LVGL face         │     ┌──────────────────────────────┴───────────┐
+│  • touch / wake word │     │  DeskLock Gateway  (container, :8600)    │
+│  • mic capture + AEC │     │  thin orchestrator — no ML dependencies  │
+│  • TTS playback      │     └───────┬──────────────────┬───────────────┘
+└──────────────────────┘             │                  │  OpenAI-format HTTP
+                                     │                  ▼
+                          HTTP (LAN) │       ┌─────────────────────────────┐
+                                     ▼       │  Speaches  (container, GPU) │
+                     ┌────────────────────┐  │  • STT: faster-whisper      │
+                     │  Tatlock (butler)  │  │  • TTS: Kokoro / Piper      │
+                     │  tatlock.schweitz. │  │  also usable by Open WebUI, │
+                     │  internal :8000    │  │  Home Assistant, …          │
+                     └────────────────────┘  └─────────────────────────────┘
 ```
 
-Tatlock stays a text-only brain. The **gateway** is Tatlock's ears and mouth: it converts
-speech to text on the way in and text to speech on the way out, keeping the device firmware
-thin (audio transport + face rendering only).
+Tatlock stays a text-only brain. The **gateway** orchestrates speech-to-text, chat, and
+text-to-speech; the **Speaches** container owns the actual STT/TTS models on the GPU,
+shared homelab-wide. The device firmware stays thin: audio transport, wake word, and
+face rendering only. Everything runs on the LAN — no cloud in the voice path.
 
 See [docs/architecture.md](docs/architecture.md) for the full design.
 
@@ -69,4 +69,5 @@ See [docs/architecture.md](docs/architecture.md) for the full design.
 - [Waveshare wiki: ESP32-P4-WIFI6-Touch-LCD-3.4C](https://www.waveshare.com/wiki/ESP32-P4-WIFI6-Touch-LCD-3.4C)
 - [Official examples repo (waveshareteam/ESP32-P4-WIFI6-Touch-LCD-XC)](https://github.com/waveshareteam/ESP32-P4-WIFI6-Touch-LCD-XC)
 - [BSP component: waveshare/esp32_p4_wifi6_touch_lcd_xc](https://components.espressif.com/components/waveshare/esp32_p4_wifi6_touch_lcd_xc)
+- [Speaches — self-hosted OpenAI-compatible speech server](https://github.com/speaches-ai/speaches)
 - Tatlock backend: `/mnt/media/Projects/tatlock` — https://tatlock.schweitz.net