# [FEATURE] Click task to open editable details

## Description
When I click a task, open details and let me update description.

## User Story
As a user, I want to click a task to view and edit its description inline.

## Technical Context
- Extends existing task display with detail view
- Requires new endpoints for fetching and updating task details
- HTMX-powered modal or slide-out panel

## Test Strategy

### Unit Test (Red)
**File:** `internal/handlers/handlers_test.go`

```go
func TestUpdateTaskDescription(t *testing.T) {
    // Setup mock Todoist client
    mockClient := &MockTodoistClient{}
    handler := NewHandler(mockClient)

    // Call update endpoint
    req := httptest.NewRequest("PUT", "/tasks/123",
        strings.NewReader(`{"description": "Updated desc"}`))

    // Assert Todoist API called with correct params
    mockClient.AssertCalled(t, "UpdateTask", "123", "Updated desc")
}
```

### E2E Test (Red)
```
1. Click on a task row
2. Assert modal/drawer opens with task details
3. Assert description field is editable
4. Edit description and save
5. Assert modal closes
6. Assert description persisted (re-open to verify)
```

## Proposed Approach

1. **Endpoints:**
   - `GET /tasks/{id}/detail` — fetch task with full details
   - `PUT /tasks/{id}` — update task (description, etc.)

2. **UI Flow:**
   - Click task row triggers `hx-get="/tasks/{id}/detail"`
   - Response loads into modal or slide-out panel
   - Form with editable description (textarea)
   - Save button triggers `hx-put="/tasks/{id}"`
   - On success, close modal and optionally update task row

3. **Template:**
   - New partial: `partials/task-detail.html`
   - Contains: title (read-only or editable), description (editable), due date, labels, save/cancel buttons

4. **API Integration:**
   - Update Todoist via API when saving
   - Update local cache

## Affected Components
- `internal/handlers/handlers.go` (new endpoints)
- `internal/handlers/handlers_test.go`
- `internal/api/todoist.go` (UpdateTask method if not exists)
- `web/templates/partials/task-detail.html` (new)
- `web/templates/partials/todoist-tasks.html` (add click handler)
- `web/templates/index.html` (modal container if needed)

## Definition of Done
- [ ] Clicking task opens detail view
- [ ] Description field is editable
- [ ] Save persists to Todoist
- [ ] Local cache updated
- [ ] Modal/drawer closes on save
- [ ] Unit tests for update handler
- [ ] E2E test for full flow