fix(postgres): map unique constraint violations to DomainError::UniqueViolation

crates/adapters/postgres/src/user.rs

@@ -166,7 +166,18 @@ impl UserWriter for PgUserRepository {
         .bind(user.updated_at)
         .execute(&self.pool)
         .await
-        .into_domain()
+        .map_err(|e| {
+            if let sqlx::Error::Database(ref db) = e {
+                if db.code().as_deref() == Some("23505") {
+                    return match db.constraint().unwrap_or("") {
+                        "users_username_key" => DomainError::UniqueViolation { field: "username" },
+                        "users_email_key"    => DomainError::UniqueViolation { field: "email" },
+                        _                   => DomainError::UniqueViolation { field: "unknown" },
+                    };
+                }
+            }
+            DomainError::Internal(e.to_string())
+        })
         .map(|_| ())
     }