## Purpose

Activity creation, chronological feed, detail views, and route linking in the Journal app.
## Requirements
### Requirement: Create activity
The Journal SHALL allow authenticated users to create an activity by uploading a GPX trace and adding a description.

#### Scenario: Create activity with GPX
- **WHEN** a user uploads a GPX file and enters a description
- **THEN** an activity is created with the GPS trace, computed distance and duration, and stored in the database

#### Scenario: Create activity linked to route
- **WHEN** a user creates an activity and selects an existing route
- **THEN** the activity is linked to that route (route_id foreign key)

### Requirement: Activity feed
The Journal SHALL display a chronological feed of the authenticated user's activities.

#### Scenario: View own activity feed
- **WHEN** a logged-in user navigates to their feed
- **THEN** they see their activities in reverse chronological order with name, date, distance, and duration

### Requirement: Activity detail page
The Journal SHALL display an activity detail page with map, stats, and description. Access depends on the activity's `visibility`: `public` activities are viewable by anyone including unauthenticated visitors, `unlisted` activities are viewable by anyone who has the URL, and `private` activities are viewable only by the owner.

#### Scenario: Owner views own activity
- **WHEN** a logged-in user navigates to an activity they own at any visibility
- **THEN** they see the activity name, description, a map with the GPS trace, distance, duration, and elevation stats

#### Scenario: Anyone views a public activity
- **WHEN** any visitor (including unauthenticated) navigates to a `public` activity's URL
- **THEN** they see the full activity detail page as above

#### Scenario: Anyone with the URL views an unlisted activity
- **WHEN** any visitor navigates directly to an `unlisted` activity's URL
- **THEN** they see the full activity detail page as above

#### Scenario: Non-owner is blocked from a private activity
- **WHEN** a visitor who is not the owner requests a `private` activity URL
- **THEN** the server responds with HTTP 404 (not 403), so the existence of the private activity is not leaked

#### Scenario: Public and unlisted activity pages emit social-share metadata
- **WHEN** a visitor loads a `public` or `unlisted` activity detail page
- **THEN** the response emits Open Graph and Twitter Card meta tags (`og:title`, `og:description`, `og:type="article"`, `og:site_name`, `twitter:card="summary"`)

### Requirement: Link activity to route
Users SHALL be able to link an existing activity to a route, or create a route from an activity trace.

#### Scenario: Link activity to existing route
- **WHEN** a user selects "Link to Route" on an activity and chooses a route
- **THEN** the activity's route_id is set to the selected route

#### Scenario: Create route from activity
- **WHEN** a user selects "Create Route from Activity"
- **THEN** a new route is created using the activity's GPX trace

### Requirement: Activity without route
Activities SHALL be allowed to exist without a linked route.

#### Scenario: Standalone activity
- **WHEN** a user imports a GPX activity without linking to a route
- **THEN** the activity is stored with route_id as null

### Requirement: Instance-wide public activity feed
The Journal SHALL expose a reverse-chronological feed of every activity on the instance with visibility `public`. This feed powers the visitor home page (see `journal-landing`) for anonymous traffic and the Public view of `/feed` (see `social-follows` spec, "Social activity feed") for signed-in viewers. `private` and `unlisted` activities SHALL NOT appear in this feed; `unlisted` stays reachable by direct URL only.

#### Scenario: Public activity appears in the visitor home feed
- **WHEN** an owner marks an activity as `public` and an anonymous visitor loads the home page
- **THEN** the visitor sees the activity in the instance feed, with the owner's display name, distance, and start date

#### Scenario: Public activity appears in the signed-in /feed?view=public view
- **WHEN** an owner marks an activity as `public` and a signed-in user loads `/feed?view=public`
- **THEN** the signed-in user sees the activity in the Public view, regardless of whether they follow the owner

#### Scenario: Private or unlisted activities stay out of the feed
- **WHEN** an activity's visibility is `private` or `unlisted`
- **THEN** it does not appear in the instance feed on either surface, regardless of who is viewing

### Requirement: Activity visibility
The Journal SHALL persist a `visibility` value on every activity and SHALL allow the owner to change it.

#### Scenario: New activities default to private
- **WHEN** an activity is created without an explicit visibility
- **THEN** the activity row is persisted with `visibility = 'private'`

#### Scenario: Owner changes an activity's visibility
- **WHEN** an activity owner selects a different visibility (`private`, `unlisted`, `public`) and saves
- **THEN** the stored visibility is updated and subsequent access checks use the new value immediately

### Requirement: Activity listings respect visibility
The Journal's own-activities feed SHALL show the owner everything regardless of visibility, while any cross-user listing SHALL only include activities with `visibility = 'public'`.

#### Scenario: Own activity feed is unchanged
- **WHEN** a logged-in user views their own activity feed
- **THEN** the feed includes all of their own activities regardless of visibility

#### Scenario: Public profile lists only public activities
- **WHEN** a visitor loads `/users/:username`
- **THEN** the rendered list of activities includes only the user's `public` activities; `unlisted` and `private` activities are omitted


### Requirement: Public activity creation fans out notifications
Creating an activity with `visibility = 'public'` SHALL enqueue a fan-out job that inserts an `activity_published` notification for every accepted follower of the activity owner. The fan-out SHALL run asynchronously so the activity-creation request returns immediately. See `notifications` spec for the notification row shape and the idempotency rules.

#### Scenario: Public activity fans out
- **WHEN** a user with N accepted followers creates an activity with `visibility = 'public'`
- **THEN** a pg-boss job is enqueued, and on completion N notifications exist with `type = 'activity_published'`, `recipient_user_id` ∈ accepted-followers, `actor_user_id` = activity owner, `subject_id` = activity id

#### Scenario: Private or unlisted activity does not fan out
- **WHEN** a user creates an activity with `visibility = 'private'` or `'unlisted'`
- **THEN** no fan-out job is enqueued and no notifications are created

#### Scenario: Visibility change to public fans out
- **WHEN** an activity owner changes an existing activity's visibility from `private` or `unlisted` to `public`
- **THEN** a fan-out job is enqueued for the visibility change, creating `activity_published` notifications for all accepted followers — the same fan-out as on initial public creation

#### Scenario: No accepted followers means no notifications
- **WHEN** a user with zero accepted followers creates a public activity
- **THEN** the fan-out job runs and inserts zero rows

### Requirement: Synthetic activity flag
The Journal SHALL persist a `synthetic` boolean on every activity so automated / demo content can be distinguished from user-created content.

#### Scenario: User-created activities default to non-synthetic
- **WHEN** an activity is created through any user-facing flow (GPX upload, sync import, Planner handoff)
- **THEN** the activity row is persisted with `synthetic = false`

#### Scenario: Bot inserts flag their rows as synthetic
- **WHEN** the demo-activity-bot inserts an activity
- **THEN** the row is persisted with `synthetic = true`

#### Scenario: Synthetic flag is not user-editable
- **WHEN** an activity owner edits the activity via any user-facing action
- **THEN** the stored `synthetic` value is not changed by the edit