Auto-RSVP attendees to Mystery Activity via slug allowlist

Mystery Activity is part of the main Thursday programming but has
kind: community, so it doesn't fit DEFAULT_PLAN_KINDS. Add a
DEFAULT_PLAN_SLUGS allowlist (initially %w[thu-mystery]) and union
it into the default_plan scope so the Mystery Activity is auto-added
to every user's plan without sweeping in the other community items
(Pre-Conference Meetup, Roundtable, Hack Day) that should remain
opt-in.

Run bin/rails plan:backfill_defaults again on existing environments
to add the Mystery Activity to existing users.

Author: Kitkatnik

app/models/schedule_item.rb

@@ -1,6 +1,9 @@
 class ScheduleItem < ApplicationRecord
   EMBASSY_MODES = %w[new_passport stamping passport_pickup].freeze
   DEFAULT_PLAN_KINDS = %w[talk reception].freeze
+  # One-off slugs that don't fit a default-plan kind but are still part of
+  # the main programming every attendee is auto-RSVPed to.
+  DEFAULT_PLAN_SLUGS = %w[thu-mystery].freeze
 
   belongs_to :created_by, class_name: "User", optional: true
   has_many :plan_items, dependent: :destroy
@@ -69,9 +72,13 @@ class ScheduleItem < ApplicationRecord
   scope :volunteer_empty, -> { volunteer.where.missing(:plan_items) }
   # Items every attendee is auto-RSVPed to on signup (and via the backfill
   # task). Restricted to public, audience: "everyone" so volunteer-only items
-  # are never auto-added to attendees' plans.
+  # are never auto-added to attendees' plans. Matches by kind OR by an
+  # explicit allowlist of slugs (for one-off items that don't fit a kind).
   scope :default_plan, -> {
-    public_items.where(audience: "everyone", kind: kinds.values_at(*DEFAULT_PLAN_KINDS))
+    public_items.where(audience: "everyone")
+                .where("kind IN (?) OR slug IN (?)",
+                       kinds.values_at(*DEFAULT_PLAN_KINDS),
+                       DEFAULT_PLAN_SLUGS)
   }
 
   # Creators always get auto-added to their own plan — whether the item is

test/models/user_test.rb

@@ -54,6 +54,22 @@ class UserTest < ActiveSupport::TestCase
     assert_not_includes user.planned_schedule_items, volunteers_only_reception, "volunteers_only items should not be auto-added to attendees"
   end
 
+  test "new user is auto-RSVPed to slug-allowlisted items even when kind isn't a default" do
+    mystery = ScheduleItem.create!(
+      slug: "thu-mystery", day: "thu", title: "Mystery Activity",
+      kind: :community, is_public: true
+    )
+    other_community = ScheduleItem.create!(
+      slug: "wed-meetup", day: "wed", title: "Pre-Conference Meetup",
+      kind: :community, is_public: true
+    )
+
+    user = User.create!(email: "mystery@example.com", first_name: "M", last_name: "Y")
+
+    assert_includes user.planned_schedule_items, mystery, "slug-allowlisted item should be auto-added"
+    assert_not_includes user.planned_schedule_items, other_community, "other community items should not auto-add"
+  end
+
   test "materialize_default_plan_items is idempotent" do
     ScheduleItem.create!(day: "thu", title: "Default Talk", kind: :talk, is_public: true)
     user = User.create!(email: "idem@example.com", first_name: "I", last_name: "D")