## ADDED Requirements

### Requirement: Translated PDF Export API

The system SHALL expose an API endpoint for downloading translated documents as PDF files.

#### Scenario: Download translated PDF via API
- **GIVEN** a task with completed translation to English
- **WHEN** POST request to `/api/v2/translate/{task_id}/pdf?lang=en`
- **THEN** system returns PDF file with translated content
- **AND** Content-Type is `application/pdf`
- **AND** Content-Disposition suggests filename like `{task_id}_translated_en.pdf`

#### Scenario: Download translated PDF with layout preservation
- **WHEN** user downloads translated PDF
- **THEN** the PDF maintains original document layout
- **AND** text positions match original document coordinates
- **AND** images and tables appear at original positions

#### Scenario: Invalid language parameter
- **GIVEN** a task with translation only to English
- **WHEN** user requests PDF with `lang=ja` (Japanese)
- **THEN** system returns 404 Not Found
- **AND** response includes available languages in error message

#### Scenario: Task not found
- **GIVEN** non-existent task_id
- **WHEN** user requests translated PDF
- **THEN** system returns 404 Not Found

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### Requirement: Frontend Translated PDF Download

The frontend SHALL provide UI controls for downloading translated PDFs.

#### Scenario: Show download button when translation complete
- **GIVEN** a task with translation status "completed"
- **WHEN** user views TaskDetailPage
- **THEN** page displays "Download Translated PDF" button
- **AND** button shows target language (e.g., "Download Translated PDF (English)")

#### Scenario: Hide download button when no translation
- **GIVEN** a task without any completed translations
- **WHEN** user views TaskDetailPage
- **THEN** "Download Translated PDF" button is not shown

#### Scenario: Download progress indication
- **GIVEN** user clicks "Download Translated PDF" button
- **WHEN** PDF generation is in progress
- **THEN** button shows loading state
- **AND** prevents double-click
- **WHEN** download completes
- **THEN** browser downloads PDF file
- **AND** button returns to normal state
