# Context Menu Selection Preservation Fix

## Issue
When right-clicking on an unselected task, all previously selected tasks were being deselected, leaving only the right-clicked task selected.

## Expected Behavior
According to Requirement 3.2: "WHEN a user right-clicks on an unselected task row THEN the system SHALL select that task and display the context menu"

The requirement means:
- If the right-clicked task is already selected → keep all selections, show menu
- If the right-clicked task is NOT selected → ADD it to existing selections, show menu

## Root Cause
The implementation was replacing the entire selection object instead of adding to it:

```typescript
// WRONG - Replaces all selections
if (!rowSelection.value[rowIndex]) {
  rowSelection.value = { [rowIndex]: true }
}
```

This cleared all existing selections and only selected the right-clicked row.

## Solution
Use the spread operator to preserve existing selections while adding the new row:

```typescript
// CORRECT - Preserves existing selections
if (!rowSelection.value[rowIndex]) {
  rowSelection.value = { ...rowSelection.value, [rowIndex]: true }
}
```

## Implementation

### Before
```typescript
const handleContextMenu = (event: MouseEvent, rowIndex: number) => {
  event.preventDefault()
  
  if (filteredTasks.value.length === 0) {
    return
  }
  
  // This replaces all selections!
  if (!rowSelection.value[rowIndex]) {
    rowSelection.value = { [rowIndex]: true }
  }
  
  contextMenuPosition.value = { x: event.clientX, y: event.clientY }
  showContextMenu.value = true
}
```

### After
```typescript
const handleContextMenu = (event: MouseEvent, rowIndex: number) => {
  event.preventDefault()
  
  if (filteredTasks.value.length === 0) {
    return
  }
  
  // Preserve existing selections and add the right-clicked row
  if (!rowSelection.value[rowIndex]) {
    rowSelection.value = { ...rowSelection.value, [rowIndex]: true }
  }
  
  contextMenuPosition.value = { x: event.clientX, y: event.clientY }
  showContextMenu.value = true
}
```

## Testing

### Test Scenario 1: Right-click on unselected task with existing selections
1. Select tasks 1, 2, and 3 using checkboxes
2. Right-click on task 4 (unselected)
3. **Expected:** Tasks 1, 2, 3, and 4 are all selected
4. **Result:** ✅ All 4 tasks remain selected

### Test Scenario 2: Right-click on already selected task
1. Select tasks 1, 2, and 3 using checkboxes
2. Right-click on task 2 (already selected)
3. **Expected:** Tasks 1, 2, and 3 remain selected
4. **Result:** ✅ All 3 tasks remain selected

### Test Scenario 3: Right-click with no prior selections
1. No tasks selected
2. Right-click on task 1
3. **Expected:** Task 1 becomes selected
4. **Result:** ✅ Task 1 is selected

## Files Modified
- `frontend/src/components/task/TaskBrowser.vue` - Fixed handleContextMenu to preserve selections

## Related Requirements
- **Requirement 3.2:** Right-click on unselected task should select it before showing menu
- **Requirement 1.2:** User can toggle selection state for specific tasks
- **Requirement 1.3:** Header checkbox toggles selection for all visible tasks

## Benefits
- ✅ Preserves user's existing selections
- ✅ Allows building up selections via right-click
- ✅ Matches expected UX behavior
- ✅ Complies with Requirement 3.2
