Add custom collections cookbook

Add an in-repository custom collections example that keeps the
bookmark domain small and focuses on dispatcher patterns.  The example
shows cursor-based pagination, URI template filtering, actor collection
links, and requester-aware followers-only collections.

Link the manual's custom collections section to the runnable example
and add a changelog entry for the accepted issue.

#694

Assisted-by: Codex:gpt-5.5

Author: dahlia

CHANGES.md

@@ -225,16 +225,23 @@ To be released.
     redistribution that threadiverse software (Lemmy, Mbin, NodeBB) uses to fan
     activity out to every subscriber.  [[#704], [#710]]
 
+ -  Added a custom collections cookbook example for bookmark-like data,
+    demonstrating cursor pagination, URI-template filtering, collection
+    counters, actor collection links, and requester-aware collections using
+    `ctx.getSignedKeyOwner()`.  [[#694], [#722]]
+
 [*Building a federated blog* tutorial]: https://fedify.dev/tutorial/astro-blog
 [Astro]: https://astro.build/
 [Bun]: https://bun.sh/
 [*Building a threadiverse community platform*]: https://fedify.dev/tutorial/threadiverse
 [*Creating your own federated microblog*]: https://fedify.dev/tutorial/microblog
 [#691]: https://github.com/fedify-dev/fedify/issues/691
+[#694]: https://github.com/fedify-dev/fedify/issues/694
 [#695]: https://github.com/fedify-dev/fedify/pull/695
 [#704]: https://github.com/fedify-dev/fedify/issues/704
 [#706]: https://github.com/fedify-dev/fedify/issues/706
 [#715]: https://github.com/fedify-dev/fedify/pull/715
+[#722]: https://github.com/fedify-dev/fedify/pull/722
 
 
 Version 2.1.10

docs/manual/collections.md

@@ -1396,12 +1396,17 @@ followers, Fedify allows you to create custom collections for your specific
 needs.  Custom collections can be used to expose any type of ActivityPub
 objects in a paginated manner.
 
+For runnable code that compares several custom collection patterns, see the
+[custom collections example].
+
 There are two types of custom collections you can create:
 
  -  **Collection**: An unordered collection of objects
  -  **Ordered Collection**: An ordered collection of objects where the order
     matters
 
+[custom collections example]: https://github.com/fedify-dev/fedify/tree/main/examples/custom-collections
+
 ### Setting up a custom collection
 
 To create a custom collection, you use either `setCollectionDispatcher()` for

examples/custom-collections/README.md

@@ -1,11 +1,28 @@
 Custom collections example
 ==========================
 
-This example demonstrates how to implement custom collections in Fedify.
-Custom collections allow you to define your own ActivityPub collections with
-custom logic for dispatching items and counting collection sizes.
+This example is a small cookbook for custom ActivityPub collections in Fedify.
+It uses a single-user bookmark log as the domain, but the important part is
+how each collection dispatcher maps server-side data to an ActivityPub
+collection.
+
+The script demonstrates three patterns:
+
+ -  `/users/alice/collections/public`: a public `OrderedCollection` with
+    cursor-based pages, `setCounter()`, `setFirstCursor()`, and
+    `setLastCursor()`.
+ -  `/users/alice/collections/tags/{tag}`: a parameterized collection that
+    filters bookmarks using a URI template value.
+ -  `/users/alice/collections/followers-only`: a collection whose result
+    depends on the signed requester.  It calls `ctx.getSignedKeyOwner()` and
+    returns an empty collection to unsigned or non-follower requests.
+
+Run it from this directory:
 
 ~~~~ sh
 deno task codegen  # At very first time only
 deno run -A ./main.ts
 ~~~~
+
+The output prints the actor document, collection metadata responses, and page
+responses for the example routes.