## ADDED Requirements

### Requirement: @Mention Support
The messaging system SHALL support @mention functionality to tag specific users in messages.

#### Scenario: Trigger mention autocomplete
- **WHEN** user types `@` in the message input
- **THEN** a dropdown menu appears showing room members
- **AND** the list filters as user continues typing
- **AND** user can select a member using keyboard or mouse

#### Scenario: Insert mention into message
- **WHEN** user selects a member from the mention dropdown
- **THEN** the mention is inserted as `@display_name`
- **AND** the mention is stored with the user_id reference
- **AND** the mention is visually highlighted in the message

#### Scenario: Mention notification
- **WHEN** a message containing @mention is sent
- **THEN** the mentioned user receives a highlighted notification
- **AND** the notification indicates they were mentioned

### Requirement: Browser Push Notifications
The system SHALL support browser push notifications for new messages.

#### Scenario: Request notification permission
- **WHEN** user first visits the chat room
- **THEN** the system prompts for notification permission
- **AND** the permission state is stored locally

#### Scenario: Send push notification
- **WHEN** a new message arrives while the tab is not focused
- **AND** user has granted notification permission
- **THEN** a browser push notification is displayed
- **AND** clicking the notification focuses the chat room

### Requirement: Sound and Vibration Alerts
The system SHALL support audio and haptic feedback for new messages.

#### Scenario: Play notification sound
- **WHEN** a new message arrives
- **AND** sound notifications are enabled
- **THEN** a notification sound is played

#### Scenario: Vibrate on mobile
- **WHEN** a new message arrives on a mobile device
- **AND** vibration is enabled
- **AND** the device supports Vibration API
- **THEN** the device vibrates briefly

### Requirement: Mention Data Storage
Messages with @mentions SHALL store the mention metadata for querying.

#### Scenario: Store mention references
- **WHEN** a message with @mentions is created
- **THEN** the `mentions` field stores an array of mentioned user_ids
- **AND** the message content preserves the @display_name format

#### Scenario: Query messages mentioning user
- **WHEN** fetching messages that mention a specific user
- **THEN** messages with that user_id in `mentions` array are returned