Add FEP-c4ad: viewership history proposal (#361)

Standard proposal for "Hide already seen posts" feature.

Reviewed-on: https://codeberg.org/fediverse/fep/pulls/361
Co-authored-by: AvidSeeker <avidseeker7@protonmail.com>
Co-committed-by: AvidSeeker <avidseeker7@protonmail.com>

fep/c4ad/fep-c4ad.md

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+---
+slug: "c4ad"
+authors: AvidSeeker <avidseeker7@protonmail.com>
+status: DRAFT
+dateReceived: 2024-07-15
+trackingIssue: 'https://codeberg.org/fediverse/fep/issues/362'
+discussionsTo: 'https://socialhub.activitypub.rocks/t/4361'
+title: Viewership History
+date: 2024-07-15
+---
+
+# FEP-c4ad: Viewership History
+
+## Summary
+
+This document proposes a standard for managing viewership history across the
+Fediverse. It addresses the common issue of posts being repeatedly shown to
+users on different clients. The goal is to enable servers to track which posts
+have been viewed by individual users and ensure that clients do not display
+these posts again. This proposal aims to enhance user experience by preventing
+the redundant display of already seen posts, commonly requested as "Hide
+already seen posts" or "stop repeating already seen posts".
+
+## Creating a Viewership Record
+
+When a user views a post, the server should create a record of this event. This
+record will include the following properties:
+
+- `id` (REQUIRED): the unique identifier of the viewership record.
+- `type` (REQUIRED): the type of the object MUST be `ViewershipRecord`.
+- `actor` (REQUIRED): the actor who viewed the post.
+- `object` (REQUIRED): the unique identifier of the post that was viewed.
+- `published` (RECOMMENDED): the date and time at which the post was viewed.
+
+## Querying Viewership Records
+
+Clients should query the server for viewership records to determine whether a
+post has been viewed by the user. The server should provide an endpoint for
+clients to fetch viewership records for a specific user.
+
+## Handling Viewed Posts
+
+When fetching posts, clients must filter out posts that have been viewed by the
+user based on the viewership records. This ensures that users are not shown the
+same posts repeatedly.
+
+## Copyright
+
+CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
+
+To the extent possible under law, the authors of this Fediverse Enhancement
+Proposal have waived all copyright and related or neighboring rights to this
+work.