[Bug]: /mission command causes Console to freeze completely

## QwenPaw Version

v1.1.7

---

## Description

执行 `/mission` 指令后，QwenPaw Console 界面会完全卡死（freeze），无法正常对话或发送新消息。进程仍在运行但界面无响应。即使清空 `~/.copaw/workspaces/default/missions/` 目录并重置 session，问题仍然会发生。

**Related PR(s):** None

**Security considerations:** 无安全风险，仅功能不可用

---

## Component(s) Affected

- [x] Core / Backend (app, agents, config, providers, utils, local_models)
- [x] Console (frontend web UI)
- [ ] Channels (DingTalk, Feishu, QQ, Discord, iMessage, etc.)
- [ ] Skills
- [ ] CLI
- [ ] Documentation (website)
- [ ] Tests
- [ ] CI/CD
- [x] Scripts / Deploy

---

## Environment

- **QwenPaw version:** Latest (May 2026) - via `qwenpaw --version` to verify
- **OS:** macOS Darwin 24.6.0 (arm64)
- **Install method:** pip / one-line install
- **Python version:** 3.12

---

## Steps to Reproduce

1. Start QwenPaw Console at `http://localhost:8088`
2. In any active conversation (main workspace or new session), type `/mission` command
3. Observe the console interface behavior

---

## Actual vs Expected

- **Actual:**
- Console interface freezes completely within seconds after `/mission` command
- No error messages displayed in UI
- Cannot send/receive new messages
- Process still running (`ps aux | grep qwenpaw` shows PID active)
- Session file remains unchanged but frozen state persists
- Requires manual intervention: reset session JSON + restart QwenPaw app to recover

- **Expected:**
- Should gracefully load missions from `~/.copaw/workspaces/default/missions/` if files exist
- If missions directory is empty or contains no valid mission files, should display "No missions available" message
- Should not crash or freeze the entire console interface

---

## Logs / Screenshots

**No visible errors in browser console or UI.**
Process status check confirms it's running but stuck:

```bash
# Command output when issue occurs
$ ps aux | grep "qwenpaw app" | grep -v grep
idominic 726 8.1 3.5 412764576 293616 ?? S 14:04PM 0:14.53 /Library/Frameworks/Python.framework/Versions/3.12/Resources/Python.app/Contents/MacOS/Python /Library/Frameworks/Python.framework/Versions/3.12/bin/qwenpaw app --host 0.0.0.0
```

**Recommended debugging:** Add logging when loading missions:

```python
# In mission loading code (if accessible):
try:
with open('~/.copaw/workspaces/default/missions/', 'r') as f:
# ... existing code
except Exception as e:
print(f"[MISSION] Error loading: {e}", file=sys.stderr)
raise # or return friendly error message to frontend
```

---

## Additional Notes

### Workaround (已验证有效)

```bash
# Step 1: Clear missions directory completely
rm -rf ~/.copaw/workspaces/default/missions/
mkdir -p ~/.copaw/workspaces/default/missions/

# Step 2: Backup and reset session
cp ~/.copaw/workspaces/default/sessions/console/console--default_console--main_hub.json \
~/Desktop/session-backup-$(date +%Y%m%d%H%M).json

# Step 3: Clear session messages (Python one-liner)
python3 -c "import json; f=open('~/.copaw/workspaces/default/sessions/console/console--default_console--main_hub.json','r+'); d=json.load(f); d['messages']=[]; f.seek(0); json.dump(d,f,indent=2)"

# Step 4: Restart QwenPaw
kill $(ps aux | grep "qwenpaw app" | grep -v grep | awk '{print $2}')
qwenpaw app
```

### Questions for Maintainers

#### 1. Is the Mission feature required?

如果 Mission 是必需功能：
- 是否需要特定的配置文件才能正常运行？
- 文档中是否说明了正确的使用方式和配置方法？
- 是否有示例 mission 文件可以参考？

如果 Mission 是可选功能：
- 是否可以默认禁用此功能？
- 是否有计划移除该功能？
- 是否有配置开关可以关闭它？

#### 2. Recommended Alternative for Task Management?

We currently manage tasks without using the official Mission feature, with a fully functional custom system:

| Function | Our Current Solution |
|----------|---------------------|
| Task Creation | `task_registry.py create_task()` → `task_registry.json` |
| Task Tracking | Custom API endpoints (`/api/tasks/*`) |
| Task Approval | Agent coordination + Git pre-commit hooks |
| Dashboard Display | Custom Dashboard (port 8765) reads JSON directly |

**Our questions:**
- Is there an official recommended alternative for task management?
- Does our current approach align with QwenPaw best practices?
- Should we integrate with the Mission feature or continue using task_registry?
- Will the Mission feature be maintained/refactured in future releases?

### System State When Issue Occurs

```
~/.copaw/workspaces/default/
├── missions/ ← Empty (only .DS_Store exists)
├── sessions/console/ ← Frozen state stored here
│ └── console--default_console--main_hub.json
├── task_registry.json ← Works perfectly (not affected)
└── dispatcher.py ← Custom routing logic
```

The mission directory being empty triggers this bug, which suggests it's a null-check missing in the code.

### Severity Assessment

- **User Impact:** High - Console becomes completely unusable until manual recovery
- **Data Loss Risk:** Low - Only session state affected, actual data (task_registry.json, memory files) preserved
- **Recovery Complexity:** Medium - Requires manual terminal commands to fix
- **Priority:** 🔴 High (should be addressed before general release)

---

*Reported by: @idominic (CoPaw Team)*
*Date: 2026-05-17T14:30+08:00*
*System: macOS Arm64*