## ADDED Requirements

### Requirement: Four-area navigation shell
The iPad app SHALL provide primary navigation among Import, Explorer, Lesson, and Study areas, adapted for iPad multi-column layout (not a Tauri/Web shell).

#### Scenario: Launch into default area
- **WHEN** the user opens the app with no active study session
- **THEN** the app shows the Import or Explorer area as the default landing surface with sidebar access to all four areas

#### Scenario: Resume active session
- **WHEN** the user opens the app and an active session exists
- **THEN** the app MAY navigate to Study with that session restored, and Lesson/Study remain reachable from navigation

### Requirement: Start lesson from selection
The app SHALL allow the user to resolve a multi-resource selection into a supported StudyMode and create a Session that can be opened in Study.

#### Scenario: Video plus PDF selection
- **WHEN** the user selects one video and one PDF in Explorer and starts a lesson
- **THEN** the system creates a session with mode `video_pdf` bound to those resources and opens Study

#### Scenario: Unsupported selection feedback
- **WHEN** the user attempts to start a lesson with a selection that cannot map to a supported StudyMode
- **THEN** the system MUST NOT create a session and MUST show a clear error or guidance message

### Requirement: Album playlist and combo
The app SHALL support albums in `playlist` and `combo` modes consistent with desktop semantics (playlist of singles; combo of multi-resource study items).

#### Scenario: Save playlist album
- **WHEN** the user builds a playlist draft from selected resources and saves it
- **THEN** the album is persisted and appears in Explorer/Lesson surfaces for later start

#### Scenario: Start combo item as lesson
- **WHEN** the user starts a lesson from a combo album item
- **THEN** the system creates or resumes a session with that item's study mode and resource bindings

### Requirement: Feature parity for MVP study modes
The app SHALL support at least these study modes in MVP UI: `single_video`, `single_audio`, `single_pdf`, `video_pdf`, `pdf_audio`.

#### Scenario: Single PDF lesson
- **WHEN** the user starts a lesson with only one PDF selected
- **THEN** Study opens in `single_pdf` mode showing the PDF content