v0.5.0 — codebase refinement, flexible API, architecture cleanup

Error handling:
  thiserror enum (NotFound/BadRequest/Unauthorized/Forbidden/Internal)
  eliminates 41 boilerplate .map_err() calls
  signature failures return 401, not 500

Named types:
  Keypair, LocalObject (with to/cc/bto/bcc addressing), Addressing

Readability:
  descriptive names everywhere, small functions, breathing room
  noisy comments removed, intent-explicit error handling (no let _ =)
  types.rs per module separating data from behavior

File organization:
  handlers/ module (actor, featured, followers, inbox, nodeinfo, outbox, webfinger)
  actors/ split (mod.rs + person.rs + types.rs)
  service/ split (builder, broadcast, collections, delivery, fetch, follow, lookup, types)
  tests next to modules

Repository traits:
  FollowRepository → 5 sub-traits (FollowerWriter/Reader, FollowingWriter/Reader, FollowMigration)
  ActorRepository → 3 sub-traits (KeypairRepository, RemoteActorCache, AnnounceRepository)
  BlocklistRepository → 2 sub-traits (DomainBlocklist, ActorBlocklist)
  supertraits with blanket impls — existing consumers unchanged
  FollowMigration has default no-op
  delete dead get_following_outbox_url

Testing:
  mock_repo! macro generates mock builders from compact specs
  MockFollowRepo, MockActorRepo, MockBlocklistRepo, MockActivityRepo,
  MockUserRepo, MockContentReader, MockObjectHandler, MockEventPublisher
  all hand-written test stubs replaced

Flexibility:
  UrlScheme trait — configurable URL patterns (DefaultUrlScheme = /users/{uuid})
  on_unknown_activity hook for custom AP extensions
  broadcast_raw_to_followers for arbitrary activity JSON
  broadcast_create/broadcast_update (renamed from Note-centric names)
  internal modules locked to pub(crate), clean public re-exports
  actor_handler, followers_handler, following_handler re-exported for custom routers

Security:
  SSRF: block IPv6-mapped private IPv4, TEST-NET, benchmarking, reserved ranges
  verify_attributed_to rejects missing/array attributedTo
  remove .expect() from outbox handler

Architecture:
  handlers/followers.rs delegates to serialize_ordered_collection (no more UrlScheme bypass)
  extract dispatch_sends, prepare_addressed_broadcast (eliminate duplication)
  DbActor::object_id(), RemoteActor::from/from_ap_person/placeholder
  send_activity unifies prepare+dispatch, deterministic_activity_id helper
  pass-through wrappers grouped in lookup.rs

src/activities/helpers.rs

@@ -47,6 +47,53 @@ pub(crate) async fn check_guards(
     Ok(false)
 }
 
+pub(crate) fn verify_attributed_to(
+    object: &serde_json::Value,
+    actor: &Url,
+    activity_name: &str,
+) -> Result<(), Error> {
+    let attributed_to = object.get("attributedTo").ok_or_else(|| {
+        Error::bad_request(format!("{activity_name} object missing attributedTo"))
+    })?;
+
+    let actor_urls: Vec<&str> = if let Some(url_str) = attributed_to.as_str() {
+        vec![url_str]
+    } else if let Some(array) = attributed_to.as_array() {
+        array
+            .iter()
+            .filter_map(|entry| {
+                entry
+                    .as_str()
+                    .or_else(|| entry.get("id").and_then(|id| id.as_str()))
+            })
+            .collect()
+    } else {
+        return Err(Error::bad_request(format!(
+            "{activity_name} object has invalid attributedTo",
+        )));
+    };
+
+    let matches_actor = actor_urls
+        .iter()
+        .any(|url_str| Url::parse(url_str).as_ref() == Ok(actor));
+
+    if !matches_actor {
+        return Err(Error::bad_request(format!(
+            "{activity_name} actor does not match object attributedTo",
+        )));
+    }
+
+    Ok(())
+}
+
+pub(crate) fn extract_object_ap_id(object: &serde_json::Value, fallback: &Url) -> Url {
+    object
+        .get("id")
+        .and_then(|value| value.as_str())
+        .and_then(|id_str| Url::parse(id_str).ok())
+        .unwrap_or_else(|| fallback.clone())
+}
+
 /// Parse `object["tag"]` for `Mention` entries and notify each tagged local user.
 /// Failures are logged and never propagated — a broken mention must not fail the activity.
 pub(crate) async fn extract_and_dispatch_mentions(
@@ -55,7 +102,7 @@ pub(crate) async fn extract_and_dispatch_mentions(
     object: &serde_json::Value,
     data: &Data<FederationData>,
 ) {
-    let Some(tags) = object.get("tag").and_then(|t| t.as_array()) else {
+    let Some(tags) = object.get("tag").and_then(|tags| tags.as_array()) else {
         return;
     };
     for tag in tags {
@@ -68,7 +115,7 @@ pub(crate) async fn extract_and_dispatch_mentions(
         let Ok(href_url) = Url::parse(href) else {
             continue;
         };
-        let Some(mentioned_user_id) = crate::urls::extract_user_id_from_url(&href_url) else {
+        let Some(mentioned_user_id) = data.url_scheme.extract_user_id(&href_url) else {
             continue;
         };
         if let Err(e) = data