github-issues/T-013.md

# T-013: Audio + Camera Device Enumeration IPC — Hot-Plug Detection, `device_list_updated` Event

**Type:** Task | **Phase:** 0 | **Autonomy:** `agent:autonomous` | **Stack:** `stack:rust`  
**Version:** v0.1 | **Iteration:** iter-1 | **Effort:** XS (1 hour)

> ⚠️ **Scope:** T-004 implemented `device_list` for audio devices only. T-013 extends it to include cameras and adds a background watcher that emits `device_list_updated` when devices are plugged or unplugged. Camera enumeration uses Windows Media Foundation (MSMF) via the `nokhwa` crate.

---

## Prerequisites
- [ ] T-002 merged — `DeviceInfo`, `DeviceKind`, `DeviceListResult` types exist
- [ ] T-004 merged — audio `device_list` command exists in `kansas/src/commands/devices.rs`

## New Workspace Dependency
```toml
nokhwa = { version = "*", features = ["input-msmf"] }  # Windows camera enumeration
```

## Acceptance Criteria
- [ ] `device_list` returns cameras alongside audio devices (kind: `"camera"`)
- [ ] Plugging in a USB camera within 3 seconds emits `device_list_updated` event to frontend
- [ ] Unplugging emits `device_list_updated`
- [ ] No panic if zero cameras present
- [ ] `cargo check --workspace` — zero errors

## Changes to `kansas/src/commands/devices.rs`

Extend the existing `device_list` command to append camera devices:

```rust
use nokhwa::{query, utils::ApiBackend};

// After audio device collection, add:
if let Ok(cameras) = query(ApiBackend::MediaFoundation) {
    for (idx, info) in cameras.iter().enumerate() {
        devices.push(DeviceInfo {
            id: id,
            name: info.human_name().to_string(),
            kind: DeviceKind::Camera,
            is_default: idx == 0,  // first camera is default
        });
        id += 1;
    }
}
```

## Add Hot-Plug Watcher

In `kansas/src/devices.rs` (new file):

```rust
use std::{sync::Arc, time::Duration, thread};
use tauri::AppHandle;
use crate::ipc::types::DeviceListResult;

/// Polls device list every 2s; emits `device_list_updated` on change.
/// Real hot-plug via WM_DEVICECHANGE is a T-013 iter-2 enhancement.
pub fn watch_devices(app: AppHandle) {
    thread::Builder::new()
        .name("synesthesia-device-watcher".into())
        .spawn(move || {
            let mut last_count = 0usize;
            loop {
                thread::sleep(Duration::from_secs(2));
                if let Ok(result) = crate::commands::devices::enumerate_all() {
                    let count = result.devices.len();
                    if count != last_count {
                        last_count = count;
                        app.emit("device_list_updated", &result).ok();
                        tracing::info!("[devices] Device list changed — {} devices", count);
                    }
                }
            }
        })
        .ok();
}
```

Register in `main.rs`: `devices::watch_devices(app_handle.clone());`

---

## GitHub CLI
```bash
gh issue create \
  --title "T-013: Audio + camera device enumeration IPC — hot-plug detection, device_list_updated" \
  --label "type:task,stack:rust,agent:autonomous,priority:high,status:ready,day:1" \
  --body-file T-013.md
```

**Parent:** GENESIS | **Blocks:** T-031 (camera config uses device IDs) | **Blocked By:** T-002, T-004