Design: start-up hook, modes, entity types; add UI-1

D20: requirement UI-1 (status in the main tab). D21: failing start-up
hook prepare() in the platform. D22: modes incl. --desktop with optional
SteamVR, --desktop-novr, --config. D23: one class per HA entity type,
native types preferred, own JSON service only as fallback.

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

docs/DESIGN.md

@@ -26,6 +26,29 @@ Three layers; dependencies only go downward (D17).
 - The overlay platform (`vrdashboard_core`) spans two layers: overlays, rendering and input
   are presentation infrastructure; SteamVR access for sensors and actions is I/O.
 
+## Start-up and modes
+
+- **Start-up hook (D21):** the platform (`DashboardApplication` in `vrdashboard_core`) gets a
+  third hook, e.g. `virtual bool prepare(QString* error)`. `exec()` calls it once mode and app
+  key are known, before the QML engine, the surfaces and `VR_Init`. On `false`, `exec()` ends
+  with exit code 1 and reports the error through the existing path (log and stderr). The
+  default returns `true`, so other apps built on the template don't change. FrameAssistant
+  loads its configuration there and decides from `mode()` whether it needs it (CFG-2).
+- **Modes (D22):**
+
+  | Mode | Configuration + HA connection | SteamVR |
+  |---|---|---|
+  | overlay (default) | yes | required (overlay app) |
+  | `--desktop` | yes | connects as background app if SteamVR runs; otherwise VR entities are unavailable (SEN-15) |
+  | `--desktop-novr` | yes | never |
+  | `--snapshot`, `--benchmark` | no | no |
+
+  - `--desktop` on the Frame over RDP shows the live UI with real data without wearing the
+    headset. Stop the SteamVR-started instance by hand first: two instances with the same
+    device name would knock each other off the broker.
+  - `--config <path>` loads another configuration file instead of
+    `~/.config/frameassistant/config.json`, e.g. on a PC with its own device name (CON-5).
+
 ## Object classes
 
 The app is HA-centric, so its building blocks follow HA's concepts (D18). Objects talk to each
@@ -34,8 +57,8 @@ and signals across threads are delivered through the receiver's event loop.
 
 | Class | Role | MVP |
 |---|---|---|
-| **HA entity** | One HA entity, both directions. Entity → HA: state and JSON attributes. HA → entity: basic commands. Observes value signals of other objects and publishes them; turns MQTT commands into signals other objects act on. Covers sensors, simple actions (`button`), settings (`switch`, `number`), feedback (`event`). | ✓ |
-| **HA service** | An action HA calls with parameters: a JSON command on an MQTT command topic (HA side: the standard `mqtt.publish` action). May be more complex than an entity command. Results go back asynchronously, e.g. through an `event` entity. How the user wraps it in HA (scripts, automations, pyscript) is their choice; FrameAssistant only requires stock HA with MQTT (NFR-6). | ✓ (notification) |
+| **HA entity** | One HA entity, both directions. Entity → HA: state and JSON attributes. HA → entity: commands; HA's MQTT integration turns its own services into them (e.g. `button.press`, `switch.turn_on`, `number.set_value`, `notify.send_message`). Observes value signals of other objects and publishes them; turns MQTT commands into signals other objects act on. **Native entity types are preferred** wherever their meaning fits (D23). | ✓ |
+| **HA service** | **Fallback** where no entity type fits (D23): a JSON command on an own MQTT command topic (HA side: the standard `mqtt.publish` action), e.g. rich notifications or vibration with parameters. Results go back asynchronously, e.g. through an `event` entity. How the user wraps it in HA (scripts, automations, pyscript) is their choice; FrameAssistant only requires stock HA with MQTT (NFR-6). | depends on the NOT-1 choice |
 | **HA device** | Owns the MQTT connection, discovery and availability, and owns all entity and service objects. One per headset (CON-5). | ✓ |
 | **I/O wrappers** | Data sources and actuators; know nothing about HA. One wrapper object per OpenVR interface used (e.g. `IVRSystem`, `IVRApplications`, `IVRChaperone`, `IVRSettings`). System wrappers (network, audio) later. | OpenVR ✓, system ✗ |
 | **Overlays** | View and controller of MVC (QML), as dashboard tabs or world overlays. Get their data (the model) from other objects. | ✓ |
@@ -44,6 +67,32 @@ and signals across threads are delivered through the receiver's event loop.
 | **Configuration** | Settings from the JSON file, loaded once by the app as an immutable value. Each component gets the part it needs through its constructor (D19). | ✓ |
 | **App** | The managing object: owns all of the above as components and wires them together. | ✓ |
 
+### Entities and services (D23)
+
+- **One class per HA entity type** on a common base. The base does the discovery part, topics,
+  availability and throttling, so SEN-14, SEN-15 and NFR-7 are handled in one place.
+- A concrete entity is an **instance with a description** (id, name, device class, unit,
+  throttle interval), not a class of its own.
+- Our actions map to native types where the meaning fits:
+
+  | Action | Type | HA service |
+  |---|---|---|
+  | Sensors (SEN-*) | `sensor`, `binary_sensor` | — |
+  | Notification (NOT-1) | `notify` | `notify.send_message` |
+  | Screenshot, standby, quit app, show boundary (SRV-1/2/3) | `button` | `button.press` |
+  | Do-not-disturb (SRV-5) | `switch` | `switch.turn_on/off` |
+  | Volume (SRV-3) | `number` | `number.set_value` |
+  | Launch app by key (SRV-2) | `text` | `text.set_value` |
+  | Attention signal with duration/volume (SRV-1), to check | `siren` | `siren.turn_on` |
+  | Feedback (NOT-5, NOT-10) | `event` | — |
+
+- **Wiring:** the app wires simple entities (I/O wrapper signal ↔ entity). Managers get their
+  entities and services from the HA device and wire them internally. The HA device owns them
+  all (D18).
+- **MQTT `notify` drops the title:** HA's `async_send_message()` renders only `message` into
+  the payload (`homeassistant/components/mqtt/notify.py`). NOT-1 needs title and text; options
+  (MVP detail): first line is the title, JSON in the message, or an own service.
+
 Notes for later:
 - OpenVR delivers all events through one queue; one dispatcher (today `VrRuntime`) hands them
   to the wrappers.
@@ -61,3 +110,6 @@ Notes for later:
 | D17 | 2026-10-05 | **Three layers:** presentation (QML), business logic, I/O. The overlay platform spans presentation (overlays, rendering, input) and I/O (SteamVR access) | Simple and enough for the start; Qt Quick already enforces separating presentation from logic |
 | D18 | 2026-10-05 | **HA-centric object classes:** HA entity, HA service, HA device, I/O wrappers, overlays, managers, HA web UI, configuration, app; communication through signals and slots | The app is HA-centric; signals/slots decouple objects and work across threads |
 | D19 | 2026-10-05 | **Configuration is injected:** the app loads it once as an immutable value and passes each component the part it needs; no singleton | Explicit dependencies, trivial tests with own configs, thread-safe; the app creates all components anyway |
+| D21 | 2026-10-05 | Start-up hook in the platform that may fail (`prepare()`), before the engine, surfaces and `VR_Init`; failure → exit code 1 | CFG-2 needs a clean abort; `loading()`/`started()` can't fail; backward compatible |
+| D22 | 2026-10-05 | Overlay and both desktop modes load the configuration and connect to HA; `--desktop` also connects to SteamVR as a background app if it runs; `--desktop-novr` never does; `--snapshot`/`--benchmark` stay without configuration; new option `--config <path>` | Live development over RDP on the Frame with real data; PC development without SteamVR under its own device name |
+| D23 | 2026-10-05 | **One class per HA entity type** on a common base; concrete entities are described instances. Native entity types (and the HA services the MQTT integration provides for them) are preferred; an own JSON command service only as fallback | Mirrors HA's model; discovery, availability and throttling in one place; actions are visible and selectable in HA without `mqtt.publish` |