[FEATURE]:TUI Bottom Bar Auto-Discovery of Sub-Sessions with Auto-Switch Management #15363

// Configuration Example
{
  "tui": {
    "status_line": {
      "subsession": {
        "enabled": true,
        "click_action": "switch_next",
        "shortcuts": {
          "switch_next": "ctrl+]",
          "switch_prev": "ctrl+[",
          "switch_picker": "<leader>s",
          "auto_switch": true
        }
      }
    }
  }
}

// Auto-Switch Configuration
{
  "subsession": {
    "auto_switch": {
      "on_create": true,       // Auto-switch when sub-session created
      "on_permission": true,   // Auto-focus when sub-session awaits permission
      "on_complete": true,     // Auto-return to parent when sub-session completes
      "on_error": false,       // Switch on sub-session error
      "exclude_agents": []     // Exclude specific agent types
    }
  }
}

// Plugin Sub-Session Event Subscription
export type PluginInput = {
  // ... existing fields
  subsession: {
    // Get child sessions of current session
    list: () => Promise<SubSessionInfo[]>;
    
    // Switch to specific sub-session
    switch: (sessionID: string) => Promise<void>;
    
    // Get parent session
    getParent: () => Promise<SessionInfo | null>;
    
    // Subscribe to sub-session changes
    on: (event: 'created' | 'updated' | 'deleted' | 'permission', 
         handler: (info: SubSessionInfo) => void) => void;
  }
}

interface SubSessionInfo {
  sessionID: string;
  parentID: string;
  agent: string;
  status: 'idle' | 'busy' | 'permission_pending' | 'completed' | 'error';
  createdAt: number;
  updatedAt: number;
  title?: string;
}

export const SubSessionMonitor = async ({ client }) => {
  client.subsession.on('permission', (info) => {
    client.tui.showToast({
      message: `Sub-task "${info.title}" requires permission`,
      variant: 'warning'
    });
  });
  
  client.subsession.on('complete', (info) => {
    // Log sub-task completion metrics
    logSubSessionMetrics(info);
  });
};

// packages/tui/src/status-line.ts
function renderSubSessionInfo() {
  const children = sync.session.getChildren(currentSessionID);
  const stats = {
    total: children.length,
    permission: children.filter(c => hasPermissionPending(c.id)).length,
    busy: children.filter(c => isBusy(c.id)).length,
    completed: children.filter(c => isCompleted(c.id)).length,
  };
  
  return `${stats.total} sub[${stats.permission}⏳ ${stats.completed}✓]`;
}

// packages/opencode/src/session/switch.ts
async function handleSubSessionEvent(event: SubSessionEvent) {
  const config = await getConfig();
  
  if (event.type === 'permission' && config.subsession.auto_switch.on_permission) {
    await switchToSession(event.sessionID);
  }
  
  if (event.type === 'complete' && config.subsession.auto_switch.on_complete) {
    const parent = await getSession(event.sessionID).parentID;
    if (parent) await switchToSession(parent);
  }
}

// packages/plugin/src/hooks.ts
export const SessionHooks = {
  'subsession.created': async (info: SubSessionInfo) => { ... },
  'subsession.updated': async (info: SubSessionInfo) => { ... },
  'subsession.deleted': async (info: SubSessionInfo) => { ... },
  'subsession.permission': async (info: SubSessionInfo) => { ... },
};