## ADDED Requirements

### Requirement: Delete selected line with keyboard
The system SHALL allow users to delete the currently selected line annotation using keyboard shortcuts (Delete key or Backspace key).

#### Scenario: Delete selected line with Delete key
- **WHEN** a line is selected (selectedLineId is set) and user presses Delete key
- **THEN** system sends DELETE request to `/api/annotations/{id}`, removes line from display, clears selection state, and triggers annotation refresh

#### Scenario: Delete selected line with Backspace key
- **WHEN** a line is selected and user presses Backspace key
- **THEN** system sends DELETE request to `/api/annotations/{id}`, removes line from display, clears selection state, and triggers annotation refresh

#### Scenario: No line selected when pressing delete
- **WHEN** no line is selected (selectedLineId is null) and user presses Delete or Backspace key
- **THEN** system takes no action and does not make any API calls

#### Scenario: Delete key during line drawing
- **WHEN** user is actively drawing a line (drawingLine state is not null) and presses Delete key
- **THEN** system cancels the line drawing operation but does NOT delete any existing lines

### Requirement: Delete all lines with confirmation
The system SHALL provide a UI button in the Toolbox to delete all line annotations at once with user confirmation.

#### Scenario: User clicks Delete All Lines button
- **WHEN** user clicks "Delete All Lines" button in Toolbox
- **THEN** system displays a confirmation dialog with message "Delete all line annotations? This cannot be undone." and Cancel/Confirm buttons

#### Scenario: User confirms delete all lines
- **WHEN** confirmation dialog is open and user clicks Confirm button
- **THEN** system sends DELETE request to `/api/annotations?type=line`, removes all lines from display, clears selection state, triggers annotation refresh, and closes dialog

#### Scenario: User cancels delete all lines
- **WHEN** confirmation dialog is open and user clicks Cancel button
- **THEN** system closes dialog without making any API calls or removing any lines

#### Scenario: No lines exist when clicking delete all
- **WHEN** user clicks "Delete All Lines" button and no line annotations exist in database
- **THEN** system still shows confirmation dialog (user confirms/cancels normally)

### Requirement: API support for bulk line deletion
The API SHALL support deleting multiple annotations by type via query parameters.

#### Scenario: Delete all lines via API
- **WHEN** DELETE request sent to `/api/annotations?type=line`
- **THEN** system deletes all annotations where label_type equals 'line' and returns `{ success: true, deleted: <count> }`

#### Scenario: Delete all annotations via API
- **WHEN** DELETE request sent to `/api/annotations?all=true`
- **THEN** system deletes all annotations regardless of type and returns `{ success: true, deleted: <count> }`

#### Scenario: Invalid type parameter
- **WHEN** DELETE request sent to `/api/annotations?type=invalid_type`
- **THEN** system returns 400 error with message "Invalid annotation type"

### Requirement: Delete button in Toolbox
The Toolbox SHALL display a "Delete All Lines" button when line annotations exist.

#### Scenario: Lines exist in database
- **WHEN** one or more line annotations exist in the database
- **THEN** Toolbox displays "Delete All Lines" button in destructive styling (red theme)

#### Scenario: No lines exist
- **WHEN** no line annotations exist in database
- **THEN** Toolbox displays "Delete All Lines" button in disabled state with reduced opacity

#### Scenario: Button position in Toolbox
- **WHEN** Toolbox renders
- **THEN** "Delete All Lines" button appears below the color picker section and above the "Delete" tool button