# Runtime and Configuration

## Backend Resolution

CLI option:

```text
scanslicer --backend {auto,wayland,x11}
```

Resolution order when `--backend auto`:

1. `QT_QPA_PLATFORM` explicit hint (`wayland`, `xcb`, `x11`)
2. `XDG_SESSION_TYPE` (`wayland` or `x11`)
3. Wayland socket presence (`XDG_RUNTIME_DIR` + `WAYLAND_DISPLAY`)
4. `DISPLAY` presence (X11)
5. fallback to Wayland

## Backend Validation

- Wayland requires:
  - `XDG_RUNTIME_DIR`
  - `WAYLAND_DISPLAY`
  - existing socket at `$XDG_RUNTIME_DIR/$WAYLAND_DISPLAY`
- X11 requires:
  - `DISPLAY`

On startup failure, ScanSlicer prints backend-specific hints to stderr.

## Qt Environment Adjustments

- For Wayland mode:
  - sets `QT_QPA_PLATFORM=wayland`
  - unsets `DISPLAY` to avoid accidental XWayland routing
- For X11 mode:
  - sets `QT_QPA_PLATFORM=xcb`
- In Flatpak/Snap:
  - defaults `QT_QPA_PLATFORMTHEME=xdgdesktopportal`
- In AppImage:
  - defaults `QT_QPA_PLATFORMTHEME=gtk3`
  - sets `QT_NO_XDG_DESKTOP_PORTAL=1`
- In container (`/.dockerenv`):
  - defaults `QT_QPA_PLATFORMTHEME=gtk3`

## Persistence Paths

### Defaults and presets

- Defaults JSON:
  - host: `~/.config/scanslicer/defaults.json`
  - container: `/work/.scanslicer/defaults.json`
  - override: `SCANSLICER_DEFAULTS_PATH`
- Presets JSON:
  - host: `~/.config/scanslicer/presets.json`
  - container: `/work/.scanslicer/presets.json`
  - override: `SCANSLICER_PRESETS_PATH`

### Auto-tune feedback

- host: `~/.config/scanslicer/autotune-feedback.json`
- container: `/work/.scanslicer/autotune-feedback.json`
- override: `SCANSLICER_FEEDBACK_PATH`

### Status log

- host: `~/.config/scanslicer/status.log`
- container: `/work/.scanslicer/status.log`
- override: `SCANSLICER_STATUS_LOG_PATH`

Legacy override names are still accepted for backward compatibility.

Status log behavior:

- new app launch truncates and starts a fresh session log
- batched flushing by time and queue size

## Container Runtime Notes

`docker-compose.yml` expects desktop/session wiring:

- `UID`, `GID` for correct file ownership
- `XDG_RUNTIME_DIR`, `WAYLAND_DISPLAY`
- mounted Wayland socket and DBus session bus
- host home mounted at `/host-home`
- project mounted at `/work`

See `.env.example` for a baseline.