feat: add PATCH /federation/me/also-known-as endpoint

Adds alsoKnownAs column to users table (migration 013), reads it in
the AP actor JSON, and exposes PATCH /federation/me/also-known-as to
set or clear it. Required pre-condition for broadcast_move.

crates/adapters/postgres-federation/src/lib.rs

@@ -546,6 +546,7 @@ impl PostgresApUserRepository {
         bio: Option<String>,
         avatar_url: Option<String>,
         header_url: Option<String>,
+        also_known_as: Option<String>,
     ) -> ApUser {
         let profile_url = url::Url::parse(&format!("{}/users/{}", self.base_url, username)).ok();
         let avatar_url = avatar_url.and_then(|u| url::Url::parse(&u).ok());
@@ -556,7 +557,7 @@ impl PostgresApUserRepository {
             bio,
             avatar_url,
             banner_url,
-            also_known_as: None,
+            also_known_as,
             profile_url,
             attachment: vec![],
         }
@@ -573,15 +574,25 @@ impl ApUserRepository for PostgresApUserRepository {
             bio: Option<String>,
             avatar_url: Option<String>,
             header_url: Option<String>,
+            also_known_as: Option<String>,
         }
         let row = sqlx::query_as::<_, Row>(
-            "SELECT id,username,bio,avatar_url,header_url FROM users WHERE id=$1 AND local=true",
+            "SELECT id,username,bio,avatar_url,header_url,also_known_as FROM users WHERE id=$1 AND local=true",
         )
         .bind(id)
         .fetch_optional(&self.pool)
         .await
         .map_err(|e| anyhow!(e))?;
-        Ok(row.map(|r| self.row_to_ap_user(r.id, r.username, r.bio, r.avatar_url, r.header_url)))
+        Ok(row.map(|r| {
+            self.row_to_ap_user(
+                r.id,
+                r.username,
+                r.bio,
+                r.avatar_url,
+                r.header_url,
+                r.also_known_as,
+            )
+        }))
     }
 
     async fn find_by_username(&self, username: &str) -> Result<Option<ApUser>> {
@@ -592,15 +603,25 @@ impl ApUserRepository for PostgresApUserRepository {
             bio: Option<String>,
             avatar_url: Option<String>,
             header_url: Option<String>,
+            also_known_as: Option<String>,
         }
         let row = sqlx::query_as::<_, Row>(
-            "SELECT id,username,bio,avatar_url,header_url FROM users WHERE username=$1 AND local=true",
+            "SELECT id,username,bio,avatar_url,header_url,also_known_as FROM users WHERE username=$1 AND local=true",
         )
         .bind(username)
         .fetch_optional(&self.pool)
         .await
         .map_err(|e| anyhow!(e))?;
-        Ok(row.map(|r| self.row_to_ap_user(r.id, r.username, r.bio, r.avatar_url, r.header_url)))
+        Ok(row.map(|r| {
+            self.row_to_ap_user(
+                r.id,
+                r.username,
+                r.bio,
+                r.avatar_url,
+                r.header_url,
+                r.also_known_as,
+            )
+        }))
     }
 
     async fn count_users(&self) -> Result<usize> {

crates/adapters/postgres/migrations/013_also_known_as.sql

@@ -0,0 +1 @@
+ALTER TABLE users ADD COLUMN IF NOT EXISTS also_known_as TEXT;

crates/adapters/postgres/src/user/mod.rs

@@ -288,6 +288,20 @@ impl UserWriter for PgUserRepository {
         .into_domain()
         .map(|_| ())
     }
+
+    async fn set_also_known_as(
+        &self,
+        user_id: &UserId,
+        value: Option<String>,
+    ) -> Result<(), DomainError> {
+        sqlx::query("UPDATE users SET also_known_as = $2, updated_at = NOW() WHERE id = $1")
+            .bind(user_id.as_uuid())
+            .bind(value)
+            .execute(&self.pool)
+            .await
+            .into_domain()
+            .map(|_| ())
+    }
 }
 
 #[cfg(test)]

crates/application/src/use_cases/auth/tests.rs

@@ -60,6 +60,13 @@ impl UserWriter for ConflictOnSaveStore {
     ) -> Result<(), DomainError> {
         self.0.update_profile(user_id, input).await
     }
+    async fn set_also_known_as(
+        &self,
+        user_id: &UserId,
+        value: Option<String>,
+    ) -> Result<(), DomainError> {
+        self.0.set_also_known_as(user_id, value).await
+    }
 }
 
 #[async_trait]
@@ -105,6 +112,13 @@ impl UserWriter for EmailConflictOnSaveStore {
     ) -> Result<(), DomainError> {
         self.0.update_profile(user_id, input).await
     }
+    async fn set_also_known_as(
+        &self,
+        user_id: &UserId,
+        value: Option<String>,
+    ) -> Result<(), DomainError> {
+        self.0.set_also_known_as(user_id, value).await
+    }
 }
 
 struct FakeHasher;

crates/domain/src/ports.rs

@@ -83,6 +83,11 @@ pub trait UserWriter: Send + Sync {
         user_id: &UserId,
         input: UpdateProfileInput,
     ) -> Result<(), DomainError>;
+    async fn set_also_known_as(
+        &self,
+        user_id: &UserId,
+        value: Option<String>,
+    ) -> Result<(), DomainError>;
 }
 
 /// Combined supertrait — `AppState.users` stays `Arc<dyn UserRepository>`.

crates/domain/src/testing/mod.rs

@@ -152,6 +152,14 @@ impl UserWriter for TestStore {
         }
         Ok(())
     }
+
+    async fn set_also_known_as(
+        &self,
+        _user_id: &UserId,
+        _value: Option<String>,
+    ) -> Result<(), DomainError> {
+        Ok(())
+    }
 }
 
 #[async_trait]

crates/presentation/src/handlers/federation_management.rs

@@ -126,3 +126,17 @@ pub async fn post_move_account(
         .map_err(ApiError::from)?;
     Ok(StatusCode::NO_CONTENT)
 }
+
+#[derive(Deserialize)]
+pub struct AlsoKnownAsBody {
+    pub also_known_as: Option<String>,
+}
+
+pub async fn patch_also_known_as(
+    Deps(d): Deps<FederationManagementDeps>,
+    AuthUser(uid): AuthUser,
+    Json(body): Json<AlsoKnownAsBody>,
+) -> Result<StatusCode, ApiError> {
+    d.users.set_also_known_as(&uid, body.also_known_as).await?;
+    Ok(StatusCode::NO_CONTENT)
+}

crates/presentation/src/routes.rs

@@ -108,6 +108,10 @@ pub fn router() -> Router<AppState> {
             "/federation/me/move",
             post(federation_management::post_move_account),
         )
+        .route(
+            "/federation/me/also-known-as",
+            patch(federation_management::patch_also_known_as),
+        )
         .route("/tags/popular", get(feed::get_popular_tags))
         .route("/tags/{name}", get(feed::tag_thoughts_handler))
         // notifications