# LCD Expressions

This document describes how LCD expressions are owned, requested, played, and
extended.

## Ownership Model

LCD expressions are split into semantic intent and low-level playback:

- `control_plane` decides when an expression should be requested.
- `domain` owns semantic expression IDs and maps them to playback requests.
- `platform` owns LCD presentation primitives and direct ST7789 drawing.

Do not bypass this path from upper layers. The expected flow is:

```text
control_plane condition
    -> domain_runtime_request_expression()
        -> platform_lcd_request_presentation()
            -> LCD direct render task
```

`control_plane` must not call `platform_lcd_*` APIs directly. `platform` must
not expose domain expression IDs.

## Current Backend State

The current LCD backend is `components/platform/src/lcd_direct.c`. It initializes
the 240x320 ST7789P3 panel directly through SPI using the
`CONFIG_TQ_SCREEN_*` pin and orientation settings, starts one render task, and
accepts the existing platform presentation requests. The 2026-07-24 board uses
MOSI GPIO18, clock GPIO8, CS GPIO15, D/C GPIO16, reset GPIO17, and backlight
GPIO7. The default X/Y swap exposes a 320x240 landscape drawing surface so the
existing LCD assets retain their current geometry.

The direct backend currently draws deterministic full-screen test patterns for
presentation requests. Real image/resource playback is the next migration step.
The previous widget-based display source files, display middleware dependency,
and legacy animation assets have been removed from the build.

## Current Expressions

| Domain expression | Trigger owner | Playback kind | Current behavior |
| --- | --- | --- | --- |
| `DOMAIN_EXPRESSION_IDLE` | LCD startup / restore path | `PLATFORM_LCD_PRESENTATION_IDLE` | Draws the direct backend idle test pattern. |
| `DOMAIN_EXPRESSION_SERVER_ERROR` | Multimodal server failure events | `PLATFORM_LCD_PRESENTATION_ASSET_SEQUENCE` | Draws a direct backend pattern selected from the mapped asset name. |
| `DOMAIN_EXPRESSION_SLOT_REELS` | Slot feature switch worker | `PLATFORM_LCD_PRESENTATION_SLOT_REELS` | Draws a direct backend slot-pattern placeholder. |
| `DOMAIN_EXPRESSION_WIFI_DISCONNECTED` | Wi-Fi state monitor worker | `PLATFORM_LCD_PRESENTATION_ASSET_SEQUENCE` | Draws a direct backend pattern selected from the mapped asset name. |
| `DOMAIN_EXPRESSION_WEALTH_SPIN` | Model-command direction worker | `PLATFORM_LCD_PRESENTATION_ASSET_SEQUENCE` | Draws a direct backend pattern selected from `spin`. |
| `DOMAIN_EXPRESSION_WEALTH_DIRECTION` | Model-command direction worker | `PLATFORM_LCD_PRESENTATION_ASSET_SEQUENCE` | Draws a direct backend pattern selected from the mapped direction asset name. |
| `DOMAIN_EXPRESSION_OTA_UPDATE` | OTA update worker | `PLATFORM_LCD_PRESENTATION_ASSET_SEQUENCE` | Loops the three-frame `ota` sequence during firmware download and installation. |

Server error currently triggers only from:

- `CONTROL_PLANE_MULTIMODAL_EVENT_TASK_FAILED`
- `CONTROL_PLANE_MULTIMODAL_EVENT_OUTPUT_ERROR`

Server error expression requests are suppressed while Wi-Fi STA is disconnected;
the Wi-Fi disconnected expression owns that state because server reachability is
not meaningful without Wi-Fi connectivity.

Transport disconnect/error events are not server error expressions.

## Asset Migration Direction

The image playback path is a platform-owned direct LCD asset pipeline. Runtime
PNG files are stored in the `gifpack` LittleFS partition, decoded through
`lodepng`, converted to RGB565 in PSRAM, and written to the ST7789 panel through
the existing bounded row-transfer buffer.

- PNG decode, the bounded four-entry LRU cache, and ST7789 writes stay inside
  `platform`.
- Domain continues to map semantic expressions to short asset IDs or names.
- Upper layers continue to use `domain_runtime_request_expression()`.
- Runtime LCD assets must be added to the explicit PNG allowlist in
  `components/platform/CMakeLists.txt`; files that only exist in the source
  directory are not packaged automatically.

## Requesting Expressions

Use `domain_runtime_request_expression()` from orchestration code:

```c
const domain_expression_request_t request = {
    .id = DOMAIN_EXPRESSION_SERVER_ERROR,
    .trigger = DOMAIN_EXPRESSION_TRIGGER_SERVER_TASK_FAILED,
};

(void)domain_runtime_request_expression(&request);
```

Trigger IDs should describe why the expression was requested. They are useful
for logs and future policy decisions, but the playback mapping is still owned by
the domain catalog.

## Playback Scheduling

The platform LCD presentation scheduler is non-blocking:

- Requests are copied at API entry.
- Panel drawing is serialized by the LCD render task.
- Same active or pending requests are coalesced.
- Higher-priority interrupting requests replace the active presentation.
- Lower-priority requests are ignored while a higher-priority presentation is
  active or pending.

Current priorities:

| Presentation | Priority | Interrupts current |
| --- | --- | --- |
| Wi-Fi disconnected / idle restore | `120` | Idle restore interrupts Wi-Fi disconnected. |
| Wealth spin / wealth-direction reveal | `110` | Yes |
| Server error | `100` | Yes |
| Slot reels | `20` | No |

## Adding a New Expression

Follow this checklist for every new expression:

1. Add a semantic ID to `domain_expression_id_t` in
   `components/domain/include/domain.h`.
2. Add a trigger reason to `domain_expression_trigger_t` if the new expression
   needs a new trigger source.
3. Add a catalog entry in `components/domain/src/runtime/domain_runtime_adapters.c`.
4. Add or map the platform direct LCD asset in the platform LCD backend.
5. Add or update the `control_plane` rule that creates
   `domain_expression_request_t`.
6. Build with the repository-approved ESP-IDF path and verify LCD logs on
   hardware.

Do not add one-off APIs such as `domain_runtime_show_happy()` or
`platform_lcd_show_error()`. Keep extension through the expression catalog and
the unified presentation request path.

## Validation Checklist

Before merging expression changes:

- Run `idf.py build` through the repository-approved ESP-IDF activation path.
- Verify `control_plane` does not include `platform.h` or call `platform_lcd_*`.
- Verify platform code does not refer to `DOMAIN_EXPRESSION_*`.
- For finite asset sequences, verify completion returns to idle when
  `return_to_idle` is set.
- For interrupting expressions, verify the active lower-priority presentation is
  cancelled cleanly.