# Phase 6: Demo-only Engine Resolution

**Status:** ⬜ Not Started
**Parent plan:** [PLAN.md](./PLAN.md)
**Domain:** backend

## Objective
Ensure demo engines are the primary/preferred engines in demo mode, and are hidden when not in demo mode. This makes demo mode act as a "virtual platform" where only demo engines resolve.

## Tasks

- [ ] Task 1: Modify `EngineRegistry.get_available_engines()` to filter out engines with `ENGINE_TYPE == "demo"` when not in demo mode (they report `is_available()=False` anyway, but belt-and-suspenders)
- [ ] Task 2: Modify `AudioEngineRegistry.get_available_engines()` similarly
- [ ] Task 3: In demo mode, `get_best_available_engine()` should return the demo engine (already handled by priority=1000, but verify)
- [ ] Task 4: Modify the `GET /api/v1/config/displays` endpoint: in demo mode, default to demo engine displays if no engine_type specified
- [ ] Task 5: Modify the audio engine listing endpoint similarly
- [ ] Task 6: Ensure `DemoDeviceProvider.discover()` only returns devices when in demo mode
- [ ] Task 7: End-to-end verification: start server in demo mode, verify only demo engines/devices appear in API responses

## Files to Modify/Create
- `server/src/wled_controller/core/capture_engines/factory.py` — Filter demo engines
- `server/src/wled_controller/core/audio/factory.py` — Filter demo engines
- `server/src/wled_controller/api/routes/system.py` — Display endpoint defaults
- `server/src/wled_controller/api/routes/audio_templates.py` — Audio engine listing
- `server/src/wled_controller/core/devices/demo_provider.py` — Guard discover()

## Acceptance Criteria
- In demo mode: demo engines are primary, real engines may also be listed but demo is default
- Not in demo mode: demo engines are completely hidden from all API responses
- Display list defaults to demo displays in demo mode
- Audio device list defaults to demo devices in demo mode

## Notes
- This is the "demo OS identifier" concept — demo mode acts as a virtual platform
- Be careful not to break existing behavior when demo=False (default)
- The demo engines already have `is_available() = is_demo_mode()`, so the main concern is UI defaults

## Review Checklist
- [ ] All tasks completed
- [ ] Code follows project conventions
- [ ] No unintended side effects
- [ ] Build passes
- [ ] Tests pass (new + existing)

## Handoff to Next Phase
<!-- Filled in after completion -->