Add shadow banning to hide users from mentoring

app/commands/mentor/discussion/retrieve.rb

@@ -33,6 +33,7 @@ def initialize(mentor,
 
   def call
     setup!
+    filter_shadow_banned!
     filter_status!
     filter_track!
     filter_student!
@@ -57,6 +58,10 @@ def setup!
       where(mentor:)
   end
 
+  def filter_shadow_banned!
+    @discussions = @discussions.joins(:solution).where.not(solutions: { user_id: User.shadow_banned.select(:id) })
+  end
+
   def filter_status!
     case status
     when :awaiting_mentor

app/commands/mentor/request/retrieve.rb

@@ -46,6 +46,9 @@ def setup!
     @requests = Mentor::Request.
       pending.
       unlocked_for(mentor)
+
+    # Shadow-banned mentors see empty queues
+    @requests = @requests.none if mentor&.shadow_banned?
   end
 
   def filter!
@@ -60,6 +63,9 @@ def filter!
         select(:student_id)
     )
 
+    # Don't show shadow-banned students' requests
+    @requests = @requests.where.not(student_id: User.shadow_banned.select(:id))
+
     if exercise_slug.present?
       filter_exercises!
     else

app/controllers/application_controller.rb

@@ -82,6 +82,12 @@ def ensure_staff!
     redirect_to maintaining_root_path
   end
 
+  def ensure_moderator!
+    return if current_user&.moderator?
+
+    redirect_to root_path
+  end
+
   def ensure_iHiD! # rubocop:disable Naming/MethodName
     return true if Rails.env.development?
     return true if current_user&.id == User::IHID_USER_ID

app/controllers/moderation/base_controller.rb

@@ -0,0 +1,5 @@
+class Moderation::BaseController < ApplicationController
+  before_action :ensure_moderator!
+
+  layout "admin"
+end

app/controllers/moderation/shadow_banned_users_controller.rb

@@ -0,0 +1,28 @@
+class Moderation::ShadowBannedUsersController < Moderation::BaseController
+  def index
+    @users = User.includes(:shadow_banned_by).where.not(shadow_banned_at: nil).order(shadow_banned_at: :desc)
+  end
+
+  def create
+    handle = params[:handle]&.strip
+    user = User.find_by(handle: handle)
+
+    if user.nil?
+      flash[:alert] = "Could not find user with handle '#{handle}'"
+    elsif user.shadow_banned?
+      flash[:alert] = "#{user.handle} is already shadow banned"
+    else
+      user.update!(shadow_banned_at: Time.current, shadow_banned_by_id: current_user.id)
+      flash[:notice] = "#{user.handle} has been shadow banned from mentoring"
+    end
+
+    redirect_to moderation_shadow_banned_users_path
+  end
+
+  def destroy
+    user = User.find_by!(handle: params[:id])
+    user.update!(shadow_banned_at: nil, shadow_banned_by_id: nil)
+    flash[:notice] = "Shadow ban removed for #{user.handle}"
+    redirect_to moderation_shadow_banned_users_path
+  end
+end

app/models/user.rb

@@ -147,6 +147,7 @@ class User < ApplicationRecord
 
   scope :with_data, -> { joins(:data) }
   scope :insiders, -> { with_data.where(user_data: { insiders_status: %i[active active_lifetime] }) }
+  scope :shadow_banned, -> { where.not(shadow_banned_at: nil) }
 
   # TODO: Validate presence of name
   validates :handle, uniqueness: { case_sensitive: false }, handle_format: true, length: { maximum: 190 }
@@ -344,9 +345,12 @@ def bought_course?
   def profile? = profile.present?
   def may_create_profile? = reputation >= User::Profile::MIN_REPUTATION
 
+  belongs_to :shadow_banned_by, class_name: "User", optional: true
+
   def confirmed? = super && !disabled? && !blocked?
   def disabled? = !!disabled_at
   def blocked? = User::BlockDomain.blocked?(user: self)
+  def shadow_banned? = !!shadow_banned_at
 
   def github_auth? = uid.present?
   def captcha_required? = !github_auth? && Time.current - created_at < 2.days

app/models/user/roles.rb

@@ -4,6 +4,7 @@ def admin? = roles.include?(:admin)
   def staff? = roles.include?(:staff) || admin?
   def maintainer? = roles.include?(:maintainer) || staff?
   def supermentor? = roles.include?(:supermentor) || staff?
+  def moderator? = roles.include?(:moderator) || staff?
   def mentor? = became_mentor_at.present? || staff?
   def roles = super.to_a.map(&:to_sym).to_set
 end

app/views/moderation/shadow_banned_users/index.html.haml

@@ -0,0 +1,31 @@
+.c-admin-table
+  .lg-container
+    %h1.text-h1.mb-8 Shadow Banned Users
+
+    - if flash[:notice]
+      .mb-12.text-p-base.font-bold.text-darkSuccessGreen= flash[:notice]
+    - if flash[:alert]
+      .mb-12.text-p-base.font-bold.text-red= flash[:alert]
+
+    = form_with(url: moderation_shadow_banned_users_path, method: :post, class: "flex items-end gap-8 mb-16") do |form|
+      .flex.flex-col
+        = form.label :handle, "User handle", class: 'text-h6 mb-4'
+        = form.text_field :handle, required: true
+      %div
+        = form.submit "Shadow Ban", class: 'btn btn-primary btn-base'
+
+    %table.mb-8{ style: "border-collapse: collapse; width: 100%; background: white;" }
+      %tr
+        %th{ style: "border: 1px solid #ddd; padding: 8px 12px; text-align: left;" } Handle
+        %th{ style: "border: 1px solid #ddd; padding: 8px 12px; text-align: left;" } Email
+        %th{ style: "border: 1px solid #ddd; padding: 8px 12px; text-align: left;" } Banned at
+        %th{ style: "border: 1px solid #ddd; padding: 8px 12px; text-align: left;" } Banned by
+        %th{ style: "border: 1px solid #ddd; padding: 8px 12px; text-align: left;" } Actions
+      - @users.each do |user|
+        %tr
+          %td{ style: "border: 1px solid #ddd; padding: 8px 12px;" }= user.handle
+          %td{ style: "border: 1px solid #ddd; padding: 8px 12px;" }= user.email
+          %td{ style: "border: 1px solid #ddd; padding: 8px 12px;" }= user.shadow_banned_at.strftime("%Y-%m-%d %H:%M")
+          %td{ style: "border: 1px solid #ddd; padding: 8px 12px;" }= user.shadow_banned_by&.handle || "Unknown"
+          %td{ style: "border: 1px solid #ddd; padding: 8px 12px;" }
+            = button_to "Remove", moderation_shadow_banned_user_path(user), method: :delete, class: 'btn btn-primary btn-base'

config/routes.rb

@@ -46,6 +46,14 @@
     resource :workflow_run_updates, only: [:create]
   end
 
+  # ########## #
+  # Moderation #
+  # ########## #
+  namespace :moderation do
+    root to: redirect('/moderation/shadow_banned_users')
+    resources :shadow_banned_users, only: %i[index create destroy]
+  end
+
   # ##### #
   # Admin #
   # ##### #

db/migrate/20260318000000_add_shadow_banned_to_users.rb

@@ -0,0 +1,9 @@
+class AddShadowBannedToUsers < ActiveRecord::Migration[7.0]
+  def change
+    return if Rails.env.production?
+
+    add_column :users, :shadow_banned_at, :datetime, null: true
+    add_column :users, :shadow_banned_by_id, :bigint, null: true
+    add_foreign_key :users, :users, column: :shadow_banned_by_id
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[7.1].define(version: 2026_02_09_141203) do
+ActiveRecord::Schema[7.1].define(version: 2026_03_18_000000) do
   create_table "active_storage_attachments", charset: "utf8mb4", collation: "utf8mb4_unicode_ci", force: :cascade do |t|
     t.string "name", null: false
     t.string "record_type", null: false
@@ -1834,6 +1834,8 @@
     t.datetime "disabled_at"
     t.integer "flair", limit: 1
     t.integer "version", limit: 2, default: 0, null: false
+    t.datetime "shadow_banned_at"
+    t.bigint "shadow_banned_by_id"
     t.index ["confirmation_token"], name: "index_users_on_confirmation_token", unique: true
     t.index ["created_at"], name: "index_users_on_created_at"
     t.index ["email"], name: "index_users_on_email", unique: true

test/commands/mentor/discussion/retrieve_test.rb

@@ -187,4 +187,16 @@ class Mentor::Discussion::RetrieveTest < ActiveSupport::TestCase
       Mentor::Discussion::Retrieve.(user, status)
     end
   end
+
+  test "does not retrieve shadow-banned students' discussions" do
+    mentor = create :user
+
+    normal_discussion = create :mentor_discussion, :awaiting_mentor, mentor: mentor
+
+    shadow_banned_discussion = create :mentor_discussion, :awaiting_mentor, mentor: mentor
+    shadow_banned_student = shadow_banned_discussion.solution.user
+    shadow_banned_student.update!(shadow_banned_at: Time.current)
+
+    assert_equal [normal_discussion], Mentor::Discussion::Retrieve.(mentor, :awaiting_mentor, page: 1)
+  end
 end

test/commands/mentor/request/retrieve_test.rb

@@ -173,4 +173,33 @@ class Mentor::Request::RetrieveTest < ActiveSupport::TestCase
     assert requests.is_a?(ActiveRecord::Relation)
     refute_respond_to requests, :current_page
   end
+
+  test "does not retrieve shadow-banned students' requests" do
+    mentored_track = create :track
+    mentor = create :user
+    create :user_track_mentorship, user: mentor, track: mentored_track
+
+    normal_student = create :user
+    banned_student = create :user, shadow_banned_at: Time.current
+
+    normal_solution = create :concept_solution, track: mentored_track, user: normal_student
+    banned_solution = create :concept_solution, track: mentored_track, user: banned_student
+
+    normal_request = create :mentor_request, solution: normal_solution
+    create :mentor_request, solution: banned_solution
+
+    assert_equal [normal_request], Mentor::Request::Retrieve.(mentor:)
+  end
+
+  test "shadow-banned mentor sees empty queue" do
+    mentored_track = create :track
+    mentor = create :user, shadow_banned_at: Time.current
+    create :user_track_mentorship, user: mentor, track: mentored_track
+
+    student = create :user
+    solution = create :concept_solution, track: mentored_track, user: student
+    create :mentor_request, solution: solution
+
+    assert_empty Mentor::Request::Retrieve.(mentor:)
+  end
 end

test/controllers/moderation/shadow_banned_users_controller_test.rb

@@ -0,0 +1,64 @@
+require "test_helper"
+
+class Moderation::ShadowBannedUsersControllerTest < ActionDispatch::IntegrationTest
+  test "index redirects if not signed in" do
+    get moderation_shadow_banned_users_url
+
+    assert_response :redirect
+  end
+
+  test "index redirects if not moderator" do
+    sign_in!
+
+    get moderation_shadow_banned_users_url
+
+    assert_response :redirect
+  end
+
+  test "index succeeds for moderator" do
+    user = create(:user, :staff)
+
+    sign_in!(user)
+
+    get moderation_shadow_banned_users_url
+
+    assert_response :success
+  end
+
+  test "create shadow bans a user" do
+    moderator = create(:user, :staff)
+    student = create :user
+
+    sign_in!(moderator)
+
+    post moderation_shadow_banned_users_url, params: { handle: student.handle }
+
+    student.reload
+    assert student.shadow_banned?
+    assert_equal moderator.id, student.shadow_banned_by_id
+    assert_redirected_to moderation_shadow_banned_users_url
+  end
+
+  test "create handles unknown handle" do
+    moderator = create(:user, :staff)
+    sign_in!(moderator)
+
+    post moderation_shadow_banned_users_url, params: { handle: "nonexistent" }
+
+    assert_redirected_to moderation_shadow_banned_users_url
+  end
+
+  test "destroy removes shadow ban" do
+    moderator = create(:user, :staff)
+    student = create :user, shadow_banned_at: Time.current, shadow_banned_by_id: moderator.id
+
+    sign_in!(moderator)
+
+    delete moderation_shadow_banned_user_url(student)
+
+    student.reload
+    refute student.shadow_banned?
+    assert_nil student.shadow_banned_by_id
+    assert_redirected_to moderation_shadow_banned_users_url
+  end
+end