backend/app/controllers/theatre_programmes_controller.rb

@@ -12,6 +12,8 @@ class TheatreProgrammesController < ApplicationController
                  .order(position: :desc).limit(100)
                  .limit(limit)
 
-    render json: programmes.as_json(include: { post: PostRepr::BASE })
+    render json: programmes.map { |programme|
+      programme.as_json.merge(post: PostRepr.base(programme.post))
+    }
   end
 end

backend/app/controllers/theatre_skip_events_controller.rb

@@ -0,0 +1,24 @@
+class TheatreSkipEventsController < ApplicationController
+  def index
+    limit = params[:limit].to_i
+    limit = 50 if limit <= 0
+
+    events =
+        TheatreSkipEvent
+        .where(theatre_id: params[:theatre_id])
+        .includes(:skipped_by_user, :users, :tags, post: { tags: :tag_name })
+        .order(created_at: :desc)
+        .limit(limit)
+
+    render json: events.map { |event|
+      { id: event.id,
+        theatre_id: event.theatre_id,
+        post: PostRepr.base(event.post),
+        skipped_by_user: UserRepr.base(event.skipped_by_user),
+        voters: event.users.map { |user| UserRepr.base(user) },
+        tags: event.tags.map { |tag| TagRepr.inline(tag) },
+        programme_position: event.programme_position,
+        created_at: event.created_at }
+    }
+  end
+end

backend/app/controllers/theatres_controller.rb

@@ -31,9 +31,7 @@ class TheatresController < ApplicationController
       post_started_at = theatre.current_post_started_at
     end
 
-    render json: {
-        host_flg:, post_id:, post_started_at:,
-        watching_users: theatre.watching_users.as_json(only: [:id, :name]) }
+    render json: theatre_info_json(theatre, host_flg:, post_id:, post_started_at:)
   end
 
   def next_post
@@ -44,14 +42,95 @@ class TheatresController < ApplicationController
     return head :forbidden if theatre.host_user != current_user
 
     ApplicationRecord.transaction do
-      post = Post.where("url LIKE '%nicovideo.jp%'")
-             .order('RAND()')
-             .first
-      theatre.update!(current_post: post, current_post_started_at: Time.current)
-      position = (theatre.programmes.maximum(:position) || 0) + 1
-      theatre.programmes.create!(position:, post:)
+      theatre.lock!
+      TheatrePostAdvancer.call(theatre:)
     end
 
     head :no_content
   end
+
+  def skip_vote
+    return head :unauthorized unless current_user
+
+    theatre = Theatre.find_by(id: params[:id])
+    return head :not_found unless theatre
+
+    skipped = false
+
+    ApplicationRecord.transaction do
+      theatre.lock!
+      if theatre.current_post
+        TheatreWatchingUser.find_or_initialize_by(theatre:, user: current_user).tap {
+          _1.expires_at = 30.seconds.from_now
+        }.save!
+
+        TheatreSkipVote.find_or_create_by!(theatre:, post: theatre.current_post, user: current_user)
+
+        vote_status = skip_vote_status(theatre)
+        if vote_status[:votes_count] >= vote_status[:required_count]
+          TheatreSkipFinalizer.call(theatre:, user: current_user)
+          TheatrePostAdvancer.call(theatre:)
+          skipped = true
+        end
+      end
+    end
+
+    theatre.reload
+    render json: theatre_info_json(theatre, skipped:)
+  end
+
+  def unskip_vote
+    return head :unauthorized unless current_user
+
+    theatre = Theatre.find_by(id: params[:id])
+    return head :not_found unless theatre
+
+    if theatre.current_post
+      TheatreSkipVote.where(theatre:, post: theatre.current_post, user: current_user).delete_all
+    end
+
+    render json: theatre_info_json(theatre, skipped: false)
+  end
+
+  def post_selection_weights
+    theatre = Theatre.find_by(id: params[:id])
+    return head :not_found unless theatre
+
+    render json: TheatrePostSelector.new(theatre:).weight_json
+  end
+
+  private
+
+  def theatre_info_json(theatre, host_flg: nil, post_id: nil, post_started_at: nil, skipped: nil)
+    host_flg = theatre.host_user_id == current_user&.id if host_flg.nil?
+    post_id = theatre.current_post_id if post_id.nil?
+    post_started_at = theatre.current_post_started_at if post_started_at.nil?
+
+    json = { host_flg:,
+             post_id:,
+             post_started_at:,
+             post_elapsed_ms: post_started_at ? ((Time.current - post_started_at) * 1000).floor : nil,
+             watching_users: theatre.watching_users.as_json(only: [:id, :name]),
+             skip_vote: skip_vote_status(theatre) }
+    json[:skipped] = skipped unless skipped.nil?
+    json
+  end
+
+  def skip_vote_status(theatre)
+    watching_user_ids = theatre.watching_users.ids
+    watching_users_count = watching_user_ids.size
+    required_count = (watching_users_count / 2) + 1
+    post = theatre.current_post
+    votes =
+        if post
+          TheatreSkipVote.where(theatre:, post:, user_id: watching_user_ids)
+        else
+          TheatreSkipVote.none
+        end
+
+    { votes_count: post ? votes.count : 0,
+      required_count:,
+      watching_users_count:,
+      voted: post && current_user ? votes.exists?(user_id: current_user.id) : false }
+  end
 end

backend/app/models/theatre.rb

@@ -8,6 +8,8 @@ class Theatre < ApplicationRecord
   has_many :watching_users, through: :active_theatre_watching_users, source: :user
 
   has_many :programmes, class_name: 'TheatreProgramme'
+  has_many :skip_votes, class_name: 'TheatreSkipVote', dependent: :delete_all
+  has_many :skip_events, class_name: 'TheatreSkipEvent', dependent: :delete_all
 
   belongs_to :host_user, class_name: 'User', optional: true
   belongs_to :current_post, class_name: 'Post', optional: true

backend/app/models/theatre_skip_event.rb

@@ -0,0 +1,10 @@
+class TheatreSkipEvent < ApplicationRecord
+  belongs_to :theatre
+  belongs_to :post
+  belongs_to :skipped_by_user, class_name: 'User'
+
+  has_many :voters, class_name: 'TheatreSkipEventVoter', dependent: :delete_all
+  has_many :event_tags, class_name: 'TheatreSkipEventTag', dependent: :delete_all
+  has_many :users, through: :voters
+  has_many :tags, through: :event_tags
+end

backend/app/models/theatre_skip_event_tag.rb

@@ -0,0 +1,6 @@
+class TheatreSkipEventTag < ApplicationRecord
+  self.primary_key = :theatre_skip_event_id, :tag_id
+
+  belongs_to :theatre_skip_event
+  belongs_to :tag
+end

backend/app/models/theatre_skip_event_voter.rb

@@ -0,0 +1,6 @@
+class TheatreSkipEventVoter < ApplicationRecord
+  self.primary_key = :theatre_skip_event_id, :user_id
+
+  belongs_to :theatre_skip_event
+  belongs_to :user
+end

backend/app/models/theatre_skip_vote.rb

@@ -0,0 +1,7 @@
+class TheatreSkipVote < ApplicationRecord
+  self.primary_key = :theatre_id, :post_id, :user_id
+
+  belongs_to :theatre
+  belongs_to :post
+  belongs_to :user
+end

backend/app/services/theatre_post_advancer.rb

@@ -0,0 +1,29 @@
+class TheatrePostAdvancer
+  def self.call(theatre:)
+    new(theatre:).call
+  end
+
+  def initialize(theatre:)
+    @theatre = theatre
+  end
+
+  def call
+    previous_post = theatre.current_post
+    post = TheatrePostSelector.new(theatre:).select
+
+    TheatreSkipVote.where(theatre:, post: previous_post).delete_all if previous_post
+
+    theatre.update!(current_post: post, current_post_started_at: post ? Time.current : nil)
+
+    if post
+      position = (theatre.programmes.maximum(:position) || 0) + 1
+      theatre.programmes.create!(position:, post:)
+    end
+
+    post
+  end
+
+  private
+
+  attr_reader :theatre
+end

backend/app/services/theatre_post_selector.rb

@@ -0,0 +1,92 @@
+class TheatrePostSelector
+  Candidate = Struct.new(:post, :weight, :penalty, :tags, keyword_init: true)
+
+  def initialize(theatre:)
+    @theatre = theatre
+  end
+
+  def select
+    candidates = weighted_candidates
+    return nil if candidates.empty?
+
+    total = candidates.sum(&:weight)
+    target = rand * total
+
+    candidates.each do |candidate|
+      target -= candidate.weight
+      return candidate.post if target <= 0
+    end
+
+    candidates.last.post
+  end
+
+  def weight_json(limit: 20)
+    candidates = weighted_candidates
+    sorted = candidates.sort_by { |candidate| [candidate.weight, candidate.post.id] }
+
+    { tag_penalties: tag_penalty_json,
+      lightest_posts: post_weight_json(sorted.first(limit)),
+      heaviest_posts: post_weight_json(sorted.reverse.first(limit)) }
+  end
+
+  private
+
+  attr_reader :theatre
+
+  def weighted_candidates
+    @weighted_candidates ||= begin
+      penalties = tag_penalties
+      posts = eligible_posts.includes(tags: :tag_name).to_a
+
+      posts.map do |post|
+        post_tags = post.tags.to_a
+        penalty = post_tags.sum { |tag| penalties[tag.id].to_i }
+        Candidate.new(post:, penalty:, tags: post_tags, weight: 1.0 / (1.0 + penalty))
+      end
+    end
+  end
+
+  def eligible_posts
+    posts = Post.where("url LIKE '%nicovideo.jp%'")
+    posts = posts.where.not(id: theatre.current_post_id) if theatre.current_post_id
+    posts
+  end
+
+  def active_user_ids
+    @active_user_ids ||= theatre.watching_users.ids
+  end
+
+  def tag_penalties
+    @tag_penalties ||=
+        if active_user_ids.empty?
+          {}
+        else
+          TheatreSkipEventVoter
+          .joins(theatre_skip_event: :event_tags)
+          .where(user_id: active_user_ids)
+          .group('theatre_skip_event_tags.tag_id')
+          .count
+        end
+  end
+
+  def tag_penalty_json
+    return [] if tag_penalties.empty?
+
+    tags = Tag.where(id: tag_penalties.keys).includes(:tag_name).index_by(&:id)
+    tag_penalties.map { |tag_id, penalty|
+      tag = tags[tag_id]
+      next unless tag
+
+      { tag: TagRepr.inline(tag), penalty: }
+    }.compact.sort_by { |row| [-row[:penalty], row[:tag]['name'].to_s] }
+  end
+
+  def post_weight_json(candidates)
+    candidates.map { |candidate|
+      { post: PostRepr.base(candidate.post),
+        weight: candidate.weight,
+        penalty: candidate.penalty,
+        tags: candidate.tags.map { |tag| TagRepr.inline(tag) } }
+    }
+  end
+end

backend/app/services/theatre_skip_finalizer.rb

@@ -0,0 +1,40 @@
+class TheatreSkipFinalizer
+  def self.call(theatre:, user:)
+    new(theatre:, user:).call
+  end
+
+  def initialize(theatre:, user:)
+    @theatre = theatre
+    @user = user
+  end
+
+  def call
+    return unless theatre.current_post
+
+    post = theatre.current_post
+    voters = TheatreSkipVote.where(theatre:, post:).includes(:user).map(&:user)
+    return if voters.empty?
+
+    event = TheatreSkipEvent.create!(
+        theatre:,
+        post:,
+        skipped_by_user: user,
+        programme_position: theatre.programmes.maximum(:position))
+
+    voters.uniq(&:id).each do |voter|
+      TheatreSkipEventVoter.create!(theatre_skip_event: event, user: voter)
+    end
+
+    post.tags.find_each do |tag|
+      TheatreSkipEventTag.create!(theatre_skip_event: event, tag:)
+    end
+
+    TheatreSkipVote.where(theatre:, post:).delete_all
+
+    event
+  end
+
+  private
+
+  attr_reader :theatre, :user
+end

backend/config/routes.rb

@@ -85,10 +85,14 @@ Rails.application.routes.draw do
     member do
       put :watching
       patch :next_post
+      put :skip_vote
+      delete :skip_vote, action: :unskip_vote
+      get :post_selection_weights
     end
 
     resources :comments, controller: :theatre_comments, only: [:index, :create, :destroy]
     resources :programmes, controller: :theatre_programmes, only: [:index]
+    resources :skip_events, controller: :theatre_skip_events, only: [:index]
   end
 
   resources :materials, only: [:index, :show, :create, :update, :destroy]

backend/db/migrate/20260606000000_create_theatre_skip_votes_and_events.rb

@@ -0,0 +1,36 @@
+class CreateTheatreSkipVotesAndEvents < ActiveRecord::Migration[8.0]
+  def change
+    create_table :theatre_skip_votes, primary_key: [:theatre_id, :post_id, :user_id] do |t|
+      t.references :theatre, null: false, foreign_key: true
+      t.references :post, null: false, foreign_key: true
+      t.references :user, null: false, foreign_key: true
+      t.timestamps
+    end
+
+    create_table :theatre_skip_events do |t|
+      t.references :theatre, null: false, foreign_key: true
+      t.references :post, null: false, foreign_key: true
+      t.references :skipped_by_user, null: false, foreign_key: { to_table: :users }
+      t.integer :programme_position
+      t.datetime :created_at, null: false
+    end
+
+    create_table :theatre_skip_event_voters, primary_key: [:theatre_skip_event_id, :user_id] do |t|
+      t.references :theatre_skip_event, null: false, foreign_key: true
+      t.references :user, null: false, foreign_key: true
+    end
+
+    create_table :theatre_skip_event_tags, primary_key: [:theatre_skip_event_id, :tag_id] do |t|
+      t.references :theatre_skip_event, null: false, foreign_key: true
+      t.references :tag, null: false, foreign_key: true
+    end
+
+    add_index :theatre_skip_events, [:theatre_id, :created_at]
+    add_index :theatre_skip_votes, [:theatre_id, :post_id, :created_at],
+              name: 'idx_theatre_skip_votes_theatre_post_created'
+    add_index :theatre_skip_event_voters, [:user_id, :theatre_skip_event_id],
+              name: 'idx_theatre_skip_event_voters_user_event'
+    add_index :theatre_skip_event_tags, [:tag_id, :theatre_skip_event_id],
+              name: 'idx_theatre_skip_event_tags_tag_event'
+  end
+end

backend/db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2026_05_14_221900) do
+ActiveRecord::Schema[8.0].define(version: 2026_06_06_000000) do
   create_table "active_storage_attachments", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "name", null: false
     t.string "record_type", null: false
@@ -137,6 +137,19 @@ ActiveRecord::Schema[8.0].define(version: 2026_05_14_221900) do
     t.index ["target_post_id"], name: "index_post_similarities_on_target_post_id"
   end
 
+  create_table "post_tag_sections", primary_key: ["post_id", "tag_id", "begin_ms"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "post_id", null: false
+    t.bigint "tag_id", null: false
+    t.integer "begin_ms", null: false
+    t.integer "end_ms", null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["post_id", "begin_ms"], name: "idx_post_tag_sections_post_id_begin_ms"
+    t.index ["tag_id"], name: "fk_rails_8be3847903"
+    t.check_constraint "`begin_ms` < `end_ms`", name: "chk_post_tag_sections_end_ms_after_begin_ms"
+    t.check_constraint "`begin_ms` >= 0", name: "chk_post_tag_sections_begin_ms_natural"
+  end
+
   create_table "post_tags", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "post_id", null: false
     t.bigint "tag_id", null: false
@@ -187,8 +200,11 @@ ActiveRecord::Schema[8.0].define(version: 2026_05_14_221900) do
     t.datetime "original_created_before"
     t.datetime "updated_at", null: false
     t.integer "version_no", null: false
+    t.integer "video_ms"
     t.index ["uploaded_user_id"], name: "index_posts_on_uploaded_user_id"
     t.index ["url"], name: "index_posts_on_url", unique: true
+    t.index ["video_ms", "id"], name: "idx_posts_video_ms_id"
+    t.check_constraint "(`video_ms` is null) or (`video_ms` > 0)", name: "chk_posts_video_ms_positive"
     t.check_constraint "`version_no` > 0", name: "chk_posts_version_no_positive"
   end
 
@@ -292,6 +308,46 @@ ActiveRecord::Schema[8.0].define(version: 2026_05_14_221900) do
     t.index ["theatre_id"], name: "index_theatre_programmes_on_theatre_id"
   end
 
+  create_table "theatre_skip_event_tags", primary_key: ["theatre_skip_event_id", "tag_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "theatre_skip_event_id", null: false
+    t.bigint "tag_id", null: false
+    t.index ["tag_id", "theatre_skip_event_id"], name: "idx_theatre_skip_event_tags_tag_event"
+    t.index ["tag_id"], name: "index_theatre_skip_event_tags_on_tag_id"
+    t.index ["theatre_skip_event_id"], name: "index_theatre_skip_event_tags_on_theatre_skip_event_id"
+  end
+
+  create_table "theatre_skip_event_voters", primary_key: ["theatre_skip_event_id", "user_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "theatre_skip_event_id", null: false
+    t.bigint "user_id", null: false
+    t.index ["theatre_skip_event_id"], name: "index_theatre_skip_event_voters_on_theatre_skip_event_id"
+    t.index ["user_id", "theatre_skip_event_id"], name: "idx_theatre_skip_event_voters_user_event"
+    t.index ["user_id"], name: "index_theatre_skip_event_voters_on_user_id"
+  end
+
+  create_table "theatre_skip_events", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "theatre_id", null: false
+    t.bigint "post_id", null: false
+    t.bigint "skipped_by_user_id", null: false
+    t.integer "programme_position"
+    t.datetime "created_at", null: false
+    t.index ["post_id"], name: "index_theatre_skip_events_on_post_id"
+    t.index ["skipped_by_user_id"], name: "index_theatre_skip_events_on_skipped_by_user_id"
+    t.index ["theatre_id", "created_at"], name: "index_theatre_skip_events_on_theatre_id_and_created_at"
+    t.index ["theatre_id"], name: "index_theatre_skip_events_on_theatre_id"
+  end
+
+  create_table "theatre_skip_votes", primary_key: ["theatre_id", "post_id", "user_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "theatre_id", null: false
+    t.bigint "post_id", null: false
+    t.bigint "user_id", null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["post_id"], name: "index_theatre_skip_votes_on_post_id"
+    t.index ["theatre_id", "post_id", "created_at"], name: "idx_theatre_skip_votes_theatre_post_created"
+    t.index ["theatre_id"], name: "index_theatre_skip_votes_on_theatre_id"
+    t.index ["user_id"], name: "index_theatre_skip_votes_on_user_id"
+  end
+
   create_table "theatre_watching_users", primary_key: ["theatre_id", "user_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "theatre_id", null: false
     t.bigint "user_id", null: false
@@ -456,6 +512,8 @@ ActiveRecord::Schema[8.0].define(version: 2026_05_14_221900) do
   add_foreign_key "post_implications", "posts", column: "parent_post_id"
   add_foreign_key "post_similarities", "posts"
   add_foreign_key "post_similarities", "posts", column: "target_post_id"
+  add_foreign_key "post_tag_sections", "posts"
+  add_foreign_key "post_tag_sections", "tags"
   add_foreign_key "post_tags", "posts"
   add_foreign_key "post_tags", "tags"
   add_foreign_key "post_tags", "users", column: "created_user_id"
@@ -476,6 +534,16 @@ ActiveRecord::Schema[8.0].define(version: 2026_05_14_221900) do
   add_foreign_key "theatre_comments", "users"
   add_foreign_key "theatre_programmes", "posts"
   add_foreign_key "theatre_programmes", "theatres"
+  add_foreign_key "theatre_skip_event_tags", "tags"
+  add_foreign_key "theatre_skip_event_tags", "theatre_skip_events"
+  add_foreign_key "theatre_skip_event_voters", "theatre_skip_events"
+  add_foreign_key "theatre_skip_event_voters", "users"
+  add_foreign_key "theatre_skip_events", "posts"
+  add_foreign_key "theatre_skip_events", "theatres"
+  add_foreign_key "theatre_skip_events", "users", column: "skipped_by_user_id"
+  add_foreign_key "theatre_skip_votes", "posts"
+  add_foreign_key "theatre_skip_votes", "theatres"
+  add_foreign_key "theatre_skip_votes", "users"
   add_foreign_key "theatre_watching_users", "theatres"
   add_foreign_key "theatre_watching_users", "users"
   add_foreign_key "theatres", "posts", column: "current_post_id"

backend/spec/requests/theatre_programmes_spec.rb

@@ -0,0 +1,31 @@
+require 'rails_helper'
+
+RSpec.describe 'TheatreProgrammes', type: :request do
+  describe 'GET /theatres/:theatre_id/programmes' do
+    let(:theatre) { create(:theatre) }
+    let(:other_theatre) { create(:theatre) }
+    let(:post_1) { Post.create!(title: 'first', url: 'https://www.nicovideo.jp/watch/sm1') }
+    let(:post_2) { Post.create!(title: 'second', url: 'https://www.nicovideo.jp/watch/sm2') }
+    let(:other_post) { Post.create!(title: 'other', url: 'https://www.nicovideo.jp/watch/sm3') }
+
+    before do
+      TheatreProgramme.create!(theatre:, position: 1, post: post_1, created_at: 2.minutes.ago)
+      TheatreProgramme.create!(theatre:, position: 2, post: post_2, created_at: 1.minute.ago)
+      TheatreProgramme.create!(
+        theatre: other_theatre,
+        position: 1,
+        post: other_post,
+        created_at: 1.minute.ago
+      )
+    end
+
+    it 'returns programmes for the theatre in descending position with post json' do
+      get "/theatres/#{theatre.id}/programmes"
+
+      expect(response).to have_http_status(:ok)
+      expect(json.map { _1['position'] }).to eq([2, 1])
+      expect(json.map { _1.dig('post', 'title') }).to eq(['second', 'first'])
+      expect(json.first['post']).to include('id' => post_2.id, 'url' => post_2.url)
+    end
+  end
+end

backend/spec/requests/theatres_spec.rb

@@ -14,10 +14,17 @@ RSpec.describe 'Theatres API', type: :request do
   let(:member) { create(:user, :member, name: 'member user') }
   let(:other_user) { create(:user, :member, name: 'other user') }
 
-  let!(:youtube_post) do
+  let!(:niconico_post) do
     Post.create!(
-      title: 'youtube post',
-      url: 'https://www.youtube.com/watch?v=spec123'
+      title: 'niconico post',
+      url: 'https://www.nicovideo.jp/watch/sm123'
+    )
+  end
+
+  let!(:second_niconico_post) do
+    Post.create!(
+      title: 'second niconico post',
+      url: 'https://www.nicovideo.jp/watch/sm456'
     )
   end
 
@@ -120,7 +127,8 @@ RSpec.describe 'Theatres API', type: :request do
         expect(json).to include(
           'host_flg' => true,
           'post_id' => nil,
-          'post_started_at' => nil
+          'post_started_at' => nil,
+          'post_elapsed_ms' => nil
         )
 
         expect(json.fetch('watching_users')).to contain_exactly(
@@ -177,7 +185,8 @@ RSpec.describe 'Theatres API', type: :request do
         expect(json).to include(
           'host_flg' => false,
           'post_id' => nil,
-          'post_started_at' => nil
+          'post_started_at' => nil,
+          'post_elapsed_ms' => nil
         )
 
         expect(json.fetch('watching_users')).to contain_exactly(
@@ -204,7 +213,7 @@ RSpec.describe 'Theatres API', type: :request do
         )
         theatre.update!(
           host_user: other_user,
-          current_post: youtube_post,
+          current_post: niconico_post,
           current_post_started_at: started_at
         )
         sign_in_as(member)
@@ -220,9 +229,11 @@ RSpec.describe 'Theatres API', type: :request do
         expect(theatre.host_user_id).to eq(member.id)
 
         expect(json['host_flg']).to eq(true)
-        expect(json['post_id']).to eq(youtube_post.id)
+        expect(json['post_id']).to eq(niconico_post.id)
         expect(Time.zone.parse(json['post_started_at']))
           .to be_within(1.second).of(started_at)
+        expect(json['post_elapsed_ms'])
+          .to be_within(1_000).of(120_000)
       end
     end
   end
@@ -273,17 +284,20 @@ RSpec.describe 'Theatres API', type: :request do
       it 'sets current_post to an eligible post and updates current_post_started_at' do
         expect { do_request }
           .to change { theatre.reload.current_post_id }
-          .from(nil).to(youtube_post.id)
 
         expect(response).to have_http_status(:no_content)
+        expect([niconico_post.id, second_niconico_post.id])
+          .to include(theatre.reload.current_post_id)
         expect(theatre.reload.current_post_started_at)
           .to be_within(1.second).of(Time.current)
+        expect(theatre.programmes.count).to eq(1)
       end
     end
 
     context 'when current user is host and no eligible post exists' do
       before do
-        youtube_post.destroy!
+        niconico_post.destroy!
+        second_niconico_post.destroy!
         theatre.update!(
           host_user: member,
           current_post: other_post,
@@ -299,9 +313,117 @@ RSpec.describe 'Theatres API', type: :request do
 
         theatre.reload
         expect(theatre.current_post_id).to be_nil
-        expect(theatre.current_post_started_at)
-          .to be_within(1.second).of(Time.current)
+        expect(theatre.current_post_started_at).to be_nil
       end
     end
   end
+
+  describe 'PUT /theatres/:id/skip_vote' do
+    subject(:do_request) do
+      put "/theatres/#{theatre.id}/skip_vote"
+    end
+
+    let(:third_user) { create(:user, :member, name: 'third user') }
+
+    before do
+      theatre.update!(current_post: niconico_post, current_post_started_at: 10.seconds.ago)
+      [member, other_user, third_user].each do |user|
+        TheatreWatchingUser.create!(
+          theatre:,
+          user:,
+          expires_at: 10.seconds.from_now
+        )
+      end
+    end
+
+    it 'records a vote and returns the current vote status before majority' do
+      sign_in_as(member)
+
+      expect { do_request }.to change(TheatreSkipVote, :count).by(1)
+
+      expect(response).to have_http_status(:ok)
+      expect(json['skipped']).to eq(false)
+      expect(json['post_id']).to eq(niconico_post.id)
+      expect(json['skip_vote']).to include(
+        'votes_count' => 1,
+        'required_count' => 2,
+        'watching_users_count' => 3,
+        'voted' => true
+      )
+    end
+
+    it 'finalizes skip when votes reach majority and stores voters and tag snapshots' do
+      tag = create(:tag, name: 'skip-target')
+      PostTag.create!(post: niconico_post, tag:)
+
+      TheatreSkipVote.create!(theatre:, post: niconico_post, user: member)
+      sign_in_as(other_user)
+
+      expect { do_request }
+        .to change(TheatreSkipEvent, :count).by(1)
+        .and change(TheatreSkipEventVoter, :count).by(2)
+        .and change(TheatreSkipEventTag, :count).by(1)
+
+      expect(response).to have_http_status(:ok)
+      expect(json['skipped']).to eq(true)
+      expect(json['post_id']).to eq(second_niconico_post.id)
+
+      event = TheatreSkipEvent.last
+      expect(event.post).to eq(niconico_post)
+      expect(event.users).to contain_exactly(member, other_user)
+      expect(event.tags).to contain_exactly(tag)
+      expect(TheatreSkipVote.where(theatre:, post: niconico_post)).to be_empty
+    end
+  end
+
+  describe 'DELETE /theatres/:id/skip_vote' do
+    before do
+      theatre.update!(current_post: niconico_post, current_post_started_at: 10.seconds.ago)
+      TheatreWatchingUser.create!(theatre:, user: member, expires_at: 10.seconds.from_now)
+      TheatreSkipVote.create!(theatre:, post: niconico_post, user: member)
+      sign_in_as(member)
+    end
+
+    it 'removes the current user vote' do
+      expect {
+        delete "/theatres/#{theatre.id}/skip_vote"
+      }.to change(TheatreSkipVote, :count).by(-1)
+
+      expect(response).to have_http_status(:ok)
+      expect(json['skip_vote']).to include(
+        'votes_count' => 0,
+        'required_count' => 1,
+        'watching_users_count' => 1,
+        'voted' => false
+      )
+    end
+  end
+
+  describe 'GET /theatres/:id/post_selection_weights' do
+    before do
+      theatre.update!(current_post: niconico_post)
+      TheatreWatchingUser.create!(theatre:, user: member, expires_at: 10.seconds.from_now)
+      sign_in_as(member)
+    end
+
+    it 'returns tag penalties and candidate weights for the current watchers' do
+      tag = create(:tag, name: 'heavy-tag')
+      PostTag.create!(post: second_niconico_post, tag:)
+      event = TheatreSkipEvent.create!(
+        theatre:,
+        post: niconico_post,
+        skipped_by_user: member,
+        created_at: Time.current
+      )
+      TheatreSkipEventVoter.create!(theatre_skip_event: event, user: member)
+      TheatreSkipEventTag.create!(theatre_skip_event: event, tag:)
+
+      get "/theatres/#{theatre.id}/post_selection_weights"
+
+      expect(response).to have_http_status(:ok)
+      expect(json['tag_penalties'].first['penalty']).to eq(1)
+      expect(json['lightest_posts'].first['post']['id']).to eq(second_niconico_post.id)
+      expect(json['lightest_posts'].first['penalty']).to eq(1)
+    end
+  end
 end

frontend/src/components/NicoViewer.tsx

@@ -37,11 +37,12 @@ type Props = {
     height:             number
     style?:             CSSProperties
     onLoadComplete?:    (info: NiconicoVideoInfo) => void
-    onMetadataChange?:  (meta: NiconicoMetadata) => void }
+    onMetadataChange?:  (meta: NiconicoMetadata) => void
+    onError?:           (data: unknown) => void }
 
 
 export default forwardRef ((props: Props, ref: ForwardedRef<NiconicoViewerHandle>) => {
-  const { id, width, height, style = { }, onLoadComplete, onMetadataChange } = props
+  const { id, width, height, style = { }, onLoadComplete, onMetadataChange, onError } = props
 
   const iframeRef = useRef<HTMLIFrameElement> (null)
   const playerId = useMemo (() => `nico-${ id }-${ Math.random ().toString (36).slice (2) }`, [id])
@@ -173,13 +174,16 @@ export default forwardRef ((props: Props, ref: ForwardedRef<NiconicoViewerHandle
 	}
 
       if (data.eventName === 'error')
+        {
           console.error ('niconico player error:', data)
+          onError?.(data)
+        }
     }
 
     addEventListener ('message', onMessage)
 
     return () => removeEventListener ('message', onMessage)
-  }, [onLoadComplete, onMetadataChange, playerId])
+  }, [onError, onLoadComplete, onMetadataChange, playerId])
 
   useLayoutEffect (() => {
     if (!(fullScreen))

frontend/src/components/PostEmbed.tsx

@@ -13,10 +13,11 @@ type Props = {
     ref?:               RefObject<NiconicoViewerHandle | null>
     post:               Post
     onLoadComplete?:    (info: NiconicoVideoInfo) => void
-    onMetadataChange?:  (meta: NiconicoMetadata) => void }
+    onMetadataChange?:  (meta: NiconicoMetadata) => void
+    onError?:           (data: unknown) => void }
 
 
-const PostEmbed: FC<Props> = ({ ref, post, onLoadComplete, onMetadataChange }) => {
+const PostEmbed: FC<Props> = ({ ref, post, onLoadComplete, onMetadataChange, onError }) => {
   const dialogue = useDialogue ()
   const [framed, setFramed] = useState (false)
 
@@ -39,7 +40,8 @@ const PostEmbed: FC<Props> = ({ ref, post, onLoadComplete, onMetadataChange }) =
 	      width={640}
 	      height={360}
 	      onLoadComplete={onLoadComplete}
-	      onMetadataChange={onMetadataChange}/>)
+	      onMetadataChange={onMetadataChange}
+	      onError={onError}/>)
     }
 
   case 'twitter.com':

frontend/src/components/TopNav.tsx

@@ -128,8 +128,12 @@ const TopNav: FC<Props> = ({ user }) => {
 
   const menu = menuOutline ({ tag, wikiId, user, pathName: location.pathname })
   const visibleMenu = menu.filter ((item): item is MenuVisibleItem => item.visible ?? true)
+  const moreMenu = menu.filter (item =>
+      !(item.visible ?? true)
+      || item.subMenu.filter (subItem => subItem.visible ?? true).length > 0)
   const activeIdx =
       visibleMenu.findIndex (item => location.pathname.startsWith (item.base || item.to))
+  const submenuHeight = moreVsbl ? 40 * moreMenu.length : (activeIdx < 0 ? 0 : 40)
 
   const prevActiveIdxRef = useRef<number> (activeIdx)
 
@@ -240,9 +244,9 @@ const TopNav: FC<Props> = ({ user }) => {
 	  <motion.div
 	      key="submenu-shell"
 	      layout
-	      className="relative hidden md:block overflow-hidden
+	      className="relative z-20 hidden md:block overflow-hidden
 			 bg-yellow-200 dark:bg-red-950"
-	      style={{ height: moreVsbl ? 40 * menu.length : (activeIdx < 0 ? 0 : 40) }}
+	      animate={{ height: submenuHeight }}
 	      onMouseLeave={() => {
 		if (moreVsbl)
 		  setMoreVsbl (false)
@@ -253,7 +257,7 @@ const TopNav: FC<Props> = ({ user }) => {
 	      }}>
 	  {moreVsbl
 	   ? (
-	      menu.map ((item, i) => (
+	      moreMenu.map ((item, i) => (
 		  <div key={i} className="relative h-[40px]">
 		    <div className="absolute inset-0 flex items-center px-3">
 		      <motion.div

frontend/src/lib/api.ts

@@ -64,11 +64,14 @@ export const apiPatch = async <T> (
 ): Promise<T> => apiP ('patch', path, body, opt)
 
 
-export const apiDelete = async (
+export const apiDelete = async <T = void> (
     path: string,
     opt?: Opt,
-): Promise<void> => {
-  await client.delete (path, withUserCode (opt))
+): Promise<T> => {
+  const res = await client.delete (path, withUserCode (opt))
+  if (res.data == null || res.data === '')
+    return undefined as T
+  return toCamel (res.data as Record<string, unknown>, { deep: true }) as T
 }
 
 

frontend/src/pages/theatres/TheatreDetailPage.tsx

@@ -1,96 +1,267 @@
-import { useEffect, useRef, useState } from 'react'
+import { motion } from 'framer-motion'
+import { useCallback, useEffect, useMemo, useRef, useState } from 'react'
 import { Helmet } from 'react-helmet-async'
 import { useParams } from 'react-router-dom'
 
 import ErrorScreen from '@/components/ErrorScreen'
+import PostEditForm from '@/components/PostEditForm'
 import PostEmbed from '@/components/PostEmbed'
 import PrefetchLink from '@/components/PrefetchLink'
-import TagDetailSidebar from '@/components/TagDetailSidebar'
+import TagLink from '@/components/TagLink'
 import FieldError from '@/components/common/FieldError'
-import SectionTitle from '@/components/common/SectionTitle'
 import { useDialogue } from '@/components/dialogues/DialogueProvider'
-import MainArea from '@/components/layout/MainArea'
-import SidebarComponent from '@/components/layout/SidebarComponent'
+import { Button } from '@/components/ui/button'
 import { SITE_TITLE } from '@/config'
-import { apiGet, apiDelete, apiPatch, apiPost, apiPut, isApiError } from '@/lib/api'
+import { CATEGORIES, CATEGORY_NAMES } from '@/consts'
+import { apiDelete, apiGet, apiPatch, apiPost, apiPut, isApiError } from '@/lib/api'
 import { fetchPost } from '@/lib/posts'
-import { dateString, inputClass } from '@/lib/utils'
+import { cn, dateString, inputClass } from '@/lib/utils'
 import { useValidationErrors } from '@/lib/useValidationErrors'
 
-import type { FC, ReactNode, User } from 'react'
+import type { FC, FormEvent, ReactNode } from 'react'
 
 import type { NiconicoMetadata,
 	      NiconicoViewerHandle,
 	      Post,
+	      Category,
+	      Tag,
 	      Theatre,
 	      TheatreComment,
-	      TheatreProgramme } from '@/types'
-
-type TheatreInfo = {
-    hostFlg:        boolean
-    postId:         number | null
-    postStartedAt:  string | null
-    watchingUsers:  { id: number; name: string }[] }
+	      TheatreInfo,
+	      TheatrePostSelectionWeights,
+	      TheatreProgramme,
+	      User } from '@/types'
 
 type TheatreCommentField = 'content'
+type TheatreLayoutMode = 'threeColumns' | 'tagsBottom' | 'commentsBottom'
+type TagFlow = 'vertical' | 'horizontal'
 
-const INITIAL_THEATRE_INFO =
+const INITIAL_THEATRE_INFO: TheatreInfo =
     { hostFlg: false,
       postId: null,
       postStartedAt: null,
-      watchingUsers: [] as { id: number; name: string }[] } as const
+      postElapsedMs: null,
+      watchingUsers: [],
+      skipVote: {
+	votesCount: 0,
+	requiredCount: 1,
+	watchingUsersCount: 0,
+	voted: false } }
+
+const INITIAL_WEIGHTS: TheatrePostSelectionWeights =
+    { tagPenalties: [], lightestPosts: [], heaviestPosts: [] }
+
+const LAYOUT_STORAGE_KEY = 'theatre-layout-mode'
+const TAG_FLOW_STORAGE_KEY = 'theatre-tag-flow'
+
+const LAYOUT_LABELS: Record<TheatreLayoutMode, string> = {
+    threeColumns:   '3 コラム',
+    tagsBottom:     'タグ下',
+    commentsBottom: 'コメント下' }
+
+const TAG_FLOW_LABELS: Record<TagFlow, string> = {
+    vertical:   'タグ縦',
+    horizontal: 'タグ横' }
 
 
-const commentBox: ReactNode[] = (comment: TheatreComment) =>
+const userName = (user: Pick<User, 'id' | 'name'> | null | undefined): string =>
+    user ? (user.name || `名もなきニジラー（#${ user.id }）`) : '運営'
+
+
+const commentBox = (
+    comment: TheatreComment,
+    programme: TheatreProgramme | null = null,
+): ReactNode[] =>
     [(
 	<div key={`${ comment.no }-content`} className="w-full">
 	  {comment.deleted
-	   ? (
-	      <span className="text-sm font-bold">
-		削除されました．
-	      </span>)
+	   ? <span className="text-sm font-bold">削除されました．</span>
 	   : comment.content}
 	</div>),
      (
 	<div key={`${ comment.no }-user`} className="w-full text-sm text-right">
-	  by {comment.user
-	      ? (comment.user.name || `名もなきニジラー（#${ comment.user.id }）`)
-	      : '運営'}
+	  by {userName (comment.user)}
 	</div>),
      (
 	<div key={`${ comment.no }-createdAt`} className="w-full text-sm text-right">
 	  {dateString (comment.createdAt)}
+	</div>),
+     (
+	<div key={`${ comment.no }-post`} className="mt-1 w-full text-xs text-zinc-500 dark:text-zinc-400">
+	  {programme ? (
+	      <>
+		この時の動画：
+		<PrefetchLink to={`/posts/${ programme.post.id }`} className="font-bold hover:underline">
+		  {programme.post.title || programme.post.url}
+		</PrefetchLink>
+	      </>) : 'この時の動画：履歴外'}
 	</div>)]
 
 
-type Props = { user: User }
+const compareTagName = (a: Tag, b: Tag): number =>
+    a.name === b.name ? 0 : (a.name < b.name ? -1 : 1)
+
+
+const tagsByCategory = (tags: Tag[]): Partial<Record<Category, Tag[]>> => {
+  const grouped: Partial<Record<Category, Tag[]>> = { }
+
+  for (const tag of tags)
+    {
+      grouped[tag.category] ??= []
+      grouped[tag.category]!.push (tag)
+    }
+
+  for (const cat of CATEGORIES)
+    grouped[cat]?.sort (compareTagName)
+
+  return grouped
+}
+
+
+const TagList: FC<{ tags: Tag[]; compact?: boolean; flow?: TagFlow }> =
+({ tags, compact, flow = 'vertical' }) => {
+  const grouped = tagsByCategory (tags)
+
+  if (flow === 'horizontal')
+    return (
+	<ul className={cn ('flex flex-wrap gap-x-3 gap-y-1', compact && 'text-sm')}>
+	  {CATEGORIES.flatMap (cat => grouped[cat] ?? []).map (tag => (
+	      <li key={tag.id} className="text-left leading-tight">
+		<TagLink tag={tag} withCount={false}/>
+	      </li>))}
+	</ul>)
+
+  return (
+      <div className="space-y-3">
+	{CATEGORIES.map (cat => {
+	  const rows = grouped[cat] ?? []
+	  if (rows.length === 0)
+	    return null
+
+	  return (
+	      <div key={cat}>
+		<div className="mb-1 shrink-0 text-xs font-bold text-zinc-500 dark:text-zinc-400">
+		  {CATEGORY_NAMES[cat]}
+		</div>
+		<ul
+		    className={cn (
+			'space-y-1',
+			compact && 'text-sm')}>
+		  {rows.map (tag => (
+		      <li key={tag.id} className="text-left leading-tight">
+			<TagLink tag={tag} withCount={false}/>
+		      </li>))}
+		</ul>
+	      </div>)
+	})}
+      </div>)
+}
+
+
+type Props = { user: User | null }
 
 
 const TheatreDetailPage: FC<Props> = ({ user }: Props) => {
   const { id } = useParams ()
-
   const dialogue = useDialogue ()
 
   const commentsRef = useRef<HTMLDivElement> (null)
   const embedRef = useRef<NiconicoViewerHandle> (null)
   const loadingRef = useRef (false)
   const theatreInfoRef = useRef<TheatreInfo> (INITIAL_THEATRE_INFO)
+  const theatreInfoReceivedAtRef = useRef (performance.now ())
   const videoLengthRef = useRef (0)
   const lastCommentNoRef = useRef (0)
 
   const [comments, setComments] = useState<TheatreComment[]> ([])
   const [content, setContent] = useState ('')
+  const [editingPost, setEditingPost] = useState<Post | null> (null)
   const [loading, setLoading] = useState (false)
+  const [programmes, setProgrammes] = useState<TheatreProgramme[]> ([])
   const [sending, setSending] = useState (false)
   const [status, setStatus] = useState (200)
   const [theatre, setTheatre] = useState<Theatre | null> (null)
   const [theatreInfo, setTheatreInfo] = useState<TheatreInfo> (INITIAL_THEATRE_INFO)
   const [post, setPost] = useState<Post | null> (null)
-  const [programmes, setProgrammes] = useState<TheatreProgramme[]> ([])
   const [videoLength, setVideoLength] = useState (0)
+  const [weights, setWeights] = useState<TheatrePostSelectionWeights> (INITIAL_WEIGHTS)
+  const [layoutMode, setLayoutMode] = useState<TheatreLayoutMode> (() => {
+    const stored = localStorage.getItem (LAYOUT_STORAGE_KEY)
+    return (['threeColumns', 'tagsBottom', 'commentsBottom'] as TheatreLayoutMode[])
+      .includes (stored as TheatreLayoutMode)
+      ? stored as TheatreLayoutMode
+      : 'threeColumns'
+  })
+  const [tagFlow, setTagFlow] = useState<TagFlow> (() => {
+    const stored = localStorage.getItem (TAG_FLOW_STORAGE_KEY)
+    return (['vertical', 'horizontal'] as TagFlow[]).includes (stored as TagFlow)
+      ? stored as TagFlow
+      : 'vertical'
+  })
   const { fieldErrors, clearValidationErrors, applyValidationError } =
       useValidationErrors<TheatreCommentField> ()
 
+  const changeLayoutMode = (mode: TheatreLayoutMode) => {
+    setLayoutMode (mode)
+    localStorage.setItem (LAYOUT_STORAGE_KEY, mode)
+  }
+
+  const changeTagFlow = (flow: TagFlow) => {
+    setTagFlow (flow)
+    localStorage.setItem (TAG_FLOW_STORAGE_KEY, flow)
+  }
+
+  const applyTheatreInfo = useCallback ((nextInfo: TheatreInfo) => {
+    theatreInfoReceivedAtRef.current = performance.now ()
+    setTheatreInfo (nextInfo)
+  }, [])
+
+  const currentPostElapsedMs = useCallback ((info: TheatreInfo = theatreInfoRef.current): number => {
+    if (info.postElapsedMs == null)
+      return 0
+
+    return Math.max (
+	info.postElapsedMs + performance.now () - theatreInfoReceivedAtRef.current,
+	0)
+  }, [])
+
+  const refreshProgrammes = useCallback (async () => {
+    if (!(id))
+      return
+
+    setProgrammes (await apiGet<TheatreProgramme[]> (
+	`/theatres/${ id }/programmes`, { params: { limit: '100' } }))
+  }, [id])
+
+  const refreshWeights = useCallback (async () => {
+    if (!(id))
+      return
+
+    setWeights (await apiGet<TheatrePostSelectionWeights> (
+	`/theatres/${ id }/post_selection_weights`))
+  }, [id])
+
+  const advancePost = useCallback (async () => {
+    if (!(id))
+      return
+
+    setLoading (true)
+    try
+    {
+      await apiPatch<void> (`/theatres/${ id }/next_post`)
+      await refreshProgrammes ()
+      await refreshWeights ()
+    }
+    catch (error)
+    {
+      console.error (error)
+    }
+    finally
+    {
+      setLoading (false)
+    }
+  }, [id, refreshProgrammes, refreshWeights])
+
   useEffect (() => {
     loadingRef.current = loading
   }, [loading])
@@ -114,10 +285,14 @@ const TheatreDetailPage: FC<Props> = ({ user }: Props) => {
     let cancelled = false
 
     setComments ([])
-    setTheatre (null)
+    setEditingPost (null)
     setPost (null)
+    setProgrammes ([])
+    setTheatre (null)
+    theatreInfoReceivedAtRef.current = performance.now ()
     setTheatreInfo (INITIAL_THEATRE_INFO)
     setVideoLength (0)
+    setWeights (INITIAL_WEIGHTS)
     lastCommentNoRef.current = 0
 
     void (async () => {
@@ -133,10 +308,13 @@ const TheatreDetailPage: FC<Props> = ({ user }: Props) => {
       }
     }) ()
 
+    void refreshProgrammes ()
+    void refreshWeights ()
+
     return () => {
       cancelled = true
     }
-  }, [id])
+  }, [id, refreshProgrammes, refreshWeights])
 
   useEffect (() => {
     if (!(id))
@@ -167,20 +345,24 @@ const TheatreDetailPage: FC<Props> = ({ user }: Props) => {
 	const ended =
 	    currentInfo.hostFlg
 	    && currentInfo.postStartedAt
-	    && ((Date.now () - (new Date (currentInfo.postStartedAt)).getTime ())
-	        > videoLengthRef.current + 3_000)
+	    && videoLengthRef.current > 0
+	    && currentPostElapsedMs (currentInfo) > videoLengthRef.current + 3_000
 
 	if (ended)
 	  {
 	    if (!(cancelled))
-	      setTheatreInfo (prev => ({ ...prev, postId: null, postStartedAt: null }))
+	      setTheatreInfo (prev => ({
+		...prev,
+		postId: null,
+		postStartedAt: null,
+		postElapsedMs: null }))
 
 	    return
 	  }
 
 	const nextInfo = await apiPut<TheatreInfo> (`/theatres/${ id }/watching`)
 	if (!(cancelled))
-	  setTheatreInfo (nextInfo)
+	  applyTheatreInfo (nextInfo)
       }
       catch (error)
       {
@@ -199,7 +381,7 @@ const TheatreDetailPage: FC<Props> = ({ user }: Props) => {
       cancelled = true
       clearInterval (interval)
     }
-  }, [id])
+  }, [applyTheatreInfo, currentPostElapsedMs, id])
 
   useEffect (() => {
     if (!(id) || !(theatreInfo.hostFlg) || loadingRef.current || theatreInfo.postId != null)
@@ -208,33 +390,24 @@ const TheatreDetailPage: FC<Props> = ({ user }: Props) => {
     let cancelled = false
 
     void (async () => {
-      setLoading (true)
-
-      try
-      {
-	await apiPatch<void> (`/theatres/${ id }/next_post`)
-      }
-      catch (error)
-      {
-	console.error (error)
-      }
-      finally
-      {
-	if (!(cancelled))
+      await advancePost ()
+      if (cancelled)
 	setLoading (false)
-      }
     }) ()
 
     return () => {
       cancelled = true
     }
-  }, [id, theatreInfo.hostFlg, theatreInfo.postId])
+  }, [advancePost, id, theatreInfo.hostFlg, theatreInfo.postId])
 
   useEffect (() => {
     setVideoLength (0)
 
     if (theatreInfo.postId == null)
+      {
+	setPost (null)
 	return
+      }
 
     let cancelled = false
 
@@ -251,31 +424,21 @@ const TheatreDetailPage: FC<Props> = ({ user }: Props) => {
       }
     }) ()
 
-    void (async () => {
-      try
-      {
-	const data = await apiGet<TheatreProgramme[]> (
-	    `/theatres/${ id }/programmes`, { params: { limit: '100' } })
-	if (!(cancelled))
-	  setProgrammes (data)
-      }
-      catch (e)
-      {
-	console.error (e)
-      }
-    }) ()
-
     return () => {
       cancelled = true
     }
-  }, [id, theatreInfo.postId])
+  }, [theatreInfo.postId])
+
+  useEffect (() => {
+    void refreshProgrammes ()
+  }, [refreshProgrammes, theatreInfo.postId])
 
   const syncPlayback = (meta: NiconicoMetadata) => {
     if (!(theatreInfo.postStartedAt))
       return
 
     const targetTime = Math.min (
-	Math.max (0, Date.now () - (new Date (theatreInfo.postStartedAt)).getTime ()),
+	currentPostElapsedMs (theatreInfo),
 	videoLength)
 
     const drift = Math.abs (meta.currentTime - targetTime)
@@ -284,6 +447,44 @@ const TheatreDetailPage: FC<Props> = ({ user }: Props) => {
       embedRef.current?.seek (targetTime)
   }
 
+  const handlePlaybackError = async () => {
+    if (!(theatreInfoRef.current.hostFlg) || loadingRef.current)
+      return
+
+    await advancePost ()
+  }
+
+  const handleSkipVote = async () => {
+    if (!(id) || !(post))
+      return
+
+    setLoading (true)
+    try
+    {
+      const nextInfo =
+	  theatreInfo.skipVote.voted
+	  ? await apiDelete<TheatreInfo> (`/theatres/${ id }/skip_vote`)
+	  : await apiPut<TheatreInfo> (`/theatres/${ id }/skip_vote`)
+
+      applyTheatreInfo (nextInfo)
+
+      if (nextInfo.skipped)
+	{
+	  setPost (null)
+	  await refreshProgrammes ()
+	  await refreshWeights ()
+	}
+    }
+    catch (error)
+    {
+      console.error (error)
+    }
+    finally
+    {
+      setLoading (false)
+    }
+  }
+
   const handleDelete = async (commentNo: number) => {
     try
     {
@@ -291,7 +492,8 @@ const TheatreDetailPage: FC<Props> = ({ user }: Props) => {
       setComments (prev => {
 	const rtn = [...prev]
 	const idx = rtn.findIndex (x => x.no === commentNo)
-	rtn[idx] = { ...rtn[idx], deleted: true }
+	if (idx >= 0)
+	  rtn[idx] = { ...rtn[idx], deleted: true, content: null }
 	return rtn
       })
     }
@@ -301,66 +503,7 @@ const TheatreDetailPage: FC<Props> = ({ user }: Props) => {
     }
   }
 
-  if (status >= 400)
-    return <ErrorScreen status={status}/>
-
-  return (
-      <div className="md:flex md:flex-1 overflow-y-auto md:overflow-y-hidden">
-	<Helmet>
-	  <meta name="robots" content="noindex"/>
-	  {theatre && (
-	      <title>
-		{'上映会場'
-		 + (theatre.name ? `『${ theatre.name }』` : ` #${ theatre.id }`)
-		 + ` | ${ SITE_TITLE }`}
-	      </title>)}
-	</Helmet>
-
-	<div className="hidden md:block">
-	  {post && <TagDetailSidebar post={post}/>}
-	</div>
-
-	<MainArea>
-	  {post ? (
-	      <>
-		<PostEmbed
-		    key={post.id}
-		    ref={embedRef}
-		    post={post}
-		    onLoadComplete={info => {
-		      embedRef.current?.play ()
-		      setVideoLength (info.lengthInSeconds * 1_000)
-		    }}
-		    onMetadataChange={syncPlayback}/>
-		<div className="m-2">
-		  <>再生中：</>
-		  <PrefetchLink to={`/posts/${ post.id }`} className="font-bold">
-		    {post.title || post.url}
-		  </PrefetchLink>
-		</div>
-	      </>) : 'Loading...'}
-
-	  <div>
-	    <SectionTitle>
-	      上映履歴
-	    </SectionTitle>
-
-	    <div>
-	      {programmes.map ((programme, i) => (
-		  <div key={i}>
-		    <PrefetchLink to={`/posts/${ programme.post.id }`}>
-		      {programme.post.title}
-		    </PrefetchLink>
-		    （{dateString (programme.createdAt)}）
-		  </div>))}
-	    </div>
-	  </div>
-	</MainArea>
-
-	<SidebarComponent>
-	  <form
-	      className="w-auto h-auto border border-black dark:border-white rounded mx-2"
-	      onSubmit={async e => {
+  const handleCommentSubmit = async (e: FormEvent) => {
     e.preventDefault ()
 
     if (!(content))
@@ -382,7 +525,61 @@ const TheatreDetailPage: FC<Props> = ({ user }: Props) => {
     {
       setSending (false)
     }
-	      }}>
+  }
+
+  const skipVote = theatreInfo.skipVote
+  const theatreTitle = theatre?.name ? `上映会場『${ theatre.name }』` : '上映会場'
+  const postTags = post?.tags ?? []
+  const programmesAsc = useMemo (
+      () => [...programmes].sort (
+	  (a, b) => Date.parse (a.createdAt) - Date.parse (b.createdAt)),
+      [programmes])
+
+  const programmeForComment = useCallback ((comment: TheatreComment): TheatreProgramme | null => {
+    const commentedAt = Date.parse (comment.createdAt)
+    let found: TheatreProgramme | null = null
+
+    for (const programme of programmesAsc)
+      {
+	const startedAt = Date.parse (programme.createdAt)
+	if (startedAt > commentedAt)
+	  break
+
+	found = programme
+      }
+
+    return found
+  }, [programmesAsc])
+
+  if (status >= 400)
+    return <ErrorScreen status={status}/>
+
+  const tagPanel = (
+      <section className="rounded border border-zinc-300 bg-white p-4 dark:border-zinc-800 dark:bg-zinc-900">
+	<div className="mb-3 flex items-center justify-between gap-3">
+	  <h2 className="font-bold">タグ</h2>
+	  {layoutMode === 'tagsBottom' && (
+	      <div className="hidden gap-2 md:flex">
+		{(Object.keys (TAG_FLOW_LABELS) as TagFlow[]).map (flow => (
+		    <Button
+			key={flow}
+			type="button"
+			size="sm"
+			variant={tagFlow === flow ? 'default' : 'outline'}
+			onClick={() => changeTagFlow (flow)}>
+		      {TAG_FLOW_LABELS[flow]}
+		    </Button>))}
+	      </div>)}
+	</div>
+	{postTags.length === 0
+	 ? <div className="text-sm text-zinc-500">タグはありません。</div>
+	 : <TagList tags={postTags} flow={layoutMode === 'tagsBottom' ? tagFlow : 'vertical'}/>}
+      </section>)
+
+  const commentsPanel = (
+      <section className="rounded border border-zinc-300 bg-white p-4 dark:border-zinc-800 dark:bg-zinc-900">
+	<h2 className="mb-3 font-bold">コメント</h2>
+	<form onSubmit={handleCommentSubmit}>
 	  <input
 	      className={inputClass ((fieldErrors.content ?? []).length > 0)}
 	      type="text"
@@ -391,22 +588,22 @@ const TheatreDetailPage: FC<Props> = ({ user }: Props) => {
 	      onChange={e => setContent (e.target.value)}
 	      disabled={sending}/>
 	  <FieldError messages={fieldErrors.content}/>
+	</form>
 
 	<div
 	    ref={commentsRef}
-		className="overflow-x-hidden overflow-y-scroll text-wrap w-full
-			   h-[32vh] md:h-[64vh] border rounded">
-	      {comments.map (comment => (
+	    className="mt-3 max-h-[48vh] overflow-y-auto rounded border border-zinc-200 dark:border-zinc-800">
+	  {comments.map (comment => {
+	    const commentProgramme = programmeForComment (comment)
+
+	    return (
 		<div
 		    key={comment.no}
-		      className="p-2 group relative rounded py-1 hover:bg-gray-100
-				 dark:hover:bg-gray-800">
+		    className="group relative border-t border-zinc-100 p-2 first:border-t-0 hover:bg-zinc-50 dark:border-zinc-800 dark:hover:bg-zinc-800">
 		  {(user && comment.user?.id === user.id && !(comment.deleted)) && (
 		      <button
 			  type="button"
-			    className="absolute left-1 top-1 hidden rounded text-md text-red-600
-				       hover:bg-red-100 group-hover:inline-block
-				       dark:text-red-300 dark:hover:bg-red-950"
+			  className="absolute left-1 top-1 hidden rounded px-1 text-red-600 hover:bg-red-100 group-hover:inline-block dark:text-red-300 dark:hover:bg-red-950"
 			  aria-label="コメントを削除"
 			  onClick={async e => {
 			    e.stopPropagation ()
@@ -414,9 +611,8 @@ const TheatreDetailPage: FC<Props> = ({ user }: Props) => {
 			    if (!(await dialogue.confirm ({
 				title: 'このコメントを削除しますか?',
 				description: (
-				      <div className="border border-black dark:border-white rounded
-						      my-3 p-2 w-64">
-					{commentBox (comment)}
+				    <div className="my-3 w-64 rounded border border-black p-2 dark:border-white">
+				      {commentBox (comment, commentProgramme)}
 				    </div>),
 				confirmText: '削除',
 				variant: 'danger' })))
@@ -426,33 +622,271 @@ const TheatreDetailPage: FC<Props> = ({ user }: Props) => {
 			  }}>
 			&times;
 		      </button>)}
-		    {commentBox (comment)}
+		  {commentBox (comment, commentProgramme)}
+		</div>)
+	  })}
+	</div>
+      </section>)
+
+  const participantsPanel = (
+      <section className="rounded border border-zinc-300 bg-white p-4 dark:border-zinc-800 dark:bg-zinc-900">
+	<h2 className="mb-3 font-bold">参加者</h2>
+	<div className="space-y-1">
+	  {theatreInfo.watchingUsers.map (watchingUser => (
+	      <div key={watchingUser.id} className="flex justify-between gap-2 text-sm">
+		<span>{userName (watchingUser)}</span>
+		{watchingUser.id === user?.id && <span className="text-zinc-500">自分</span>}
 	      </div>))}
 	</div>
-	  </form>
+      </section>)
 
-	  <div className="w-auto h-auto border border-black dark:border-white rounded mx-2 mt-4">
-	    <div className="p-2">
-		現在の同接数：{theatreInfo.watchingUsers.length}
+  const historyPanel = (
+      <section className="rounded border border-zinc-300 bg-white p-4 dark:border-zinc-800 dark:bg-zinc-900">
+	<h2 className="mb-3 font-bold">再生履歴</h2>
+	<div className="max-h-72 overflow-y-auto">
+	  {programmes.length === 0 ? (
+	      <div className="text-sm text-zinc-500">まだ履歴はありません。</div>) : programmes.map (programme => (
+	      <div key={`${ programme.theatreId }-${ programme.position }`} className="border-t border-zinc-100 py-2 text-sm first:border-t-0 dark:border-zinc-800">
+		<PrefetchLink to={`/posts/${ programme.post.id }`} className="font-bold hover:underline">
+		  {programme.post.title || programme.post.url}
+		</PrefetchLink>
+		<div className="text-xs text-zinc-500">
+		  #{programme.position} / {dateString (programme.createdAt)}
+		</div>
+	      </div>))}
+	</div>
+      </section>)
+
+  const weightsPanel = (
+      <section className="rounded border border-zinc-300 bg-white p-4 dark:border-zinc-800 dark:bg-zinc-900">
+	<div className="mb-3 flex items-center justify-between gap-3">
+	  <h2 className="font-bold">今の抽選重み</h2>
+	  <Button type="button" variant="outline" size="sm" onClick={() => void refreshWeights ()}>
+	    更新
+	  </Button>
 	</div>
 
-	    <div className="overflow-x-hidden overflow-y-scroll text-wrap w-full h-32
-			    border rounded">
-	      <ul className="list-inside list-disc">
-		{theatreInfo.watchingUsers.map (user => (
-		    <li key={user.id} className="px-4 py-1 text-sm">
-		      {user.name || `名もなきニジラー（#${ user.id }）`}
-		    </li>))}
-	      </ul>
+	<div className="grid gap-4 xl:grid-cols-3">
+	  <div>
+	    <h3 className="mb-2 text-sm font-bold">下がってゐるタグ</h3>
+	    <div className="space-y-1 text-sm">
+	      {weights.tagPenalties.length === 0 ? (
+		  <div className="text-zinc-500">まだ減点はありません。</div>) : weights.tagPenalties.slice (0, 12).map (row => (
+		  <div key={row.tag.id} className="grid grid-cols-[minmax(0,1fr)_auto] items-baseline gap-2 text-left">
+		    <div className="min-w-0 text-left">
+		      <TagLink tag={row.tag} withCount={false}/>
+		    </div>
+		    <span className="font-mono">{row.penalty}</span>
+		  </div>))}
 	    </div>
 	  </div>
-	</SidebarComponent>
+
+	  <div>
+	    <h3 className="mb-2 text-sm font-bold">出にくい候補</h3>
+	    <WeightRows rows={weights.lightestPosts}/>
+	  </div>
+
+	  <div>
+	    <h3 className="mb-2 text-sm font-bold">出やすい候補</h3>
+	    <WeightRows rows={weights.heaviestPosts}/>
+	  </div>
+	</div>
+      </section>)
+
+  return (
+      <motion.div
+	  layout="position"
+	  transition={{ layout: { duration: .2, ease: 'easeOut' } }}
+	  className="min-h-0 flex-1 overflow-y-auto bg-zinc-50 text-zinc-950 md:overflow-hidden dark:bg-zinc-950 dark:text-zinc-50">
+	<Helmet>
+	  <meta name="robots" content="noindex"/>
+	  {theatre && <title>{`${ theatreTitle } | ${ SITE_TITLE }`}</title>}
+	</Helmet>
+
+	<div className={cn (
+	    'grid min-h-full gap-4 overflow-visible p-3 md:h-full md:overflow-hidden',
+	    layoutMode === 'threeColumns' && 'md:grid-cols-[16rem_minmax(0,1fr)_22rem] xl:grid-cols-[18rem_minmax(0,1fr)_24rem]',
+	    layoutMode === 'tagsBottom' && 'md:grid-cols-[minmax(0,1fr)_22rem] xl:grid-cols-[minmax(0,1fr)_24rem]',
+	    layoutMode === 'commentsBottom' && 'md:grid-cols-[16rem_minmax(0,1fr)] xl:grid-cols-[18rem_minmax(0,1fr)]')}>
+	  {layoutMode !== 'tagsBottom' && (
+	      <motion.aside
+		  layout="position"
+		  className="hidden min-w-0 space-y-4 md:order-none md:block md:overflow-y-auto md:[direction:rtl]">
+		<div className="md:[direction:ltr]">
+		  {tagPanel}
+		</div>
+	      </motion.aside>)}
+
+	  <motion.main
+	      layout="position"
+	      className={cn (
+		  'order-1 min-w-0 space-y-4 md:order-none md:overflow-y-auto',
+		  layoutMode === 'tagsBottom' && 'md:[direction:rtl]')}>
+	    <div className={cn (layoutMode === 'tagsBottom' && 'md:[direction:ltr]')}>
+	    <section className="overflow-hidden rounded border border-zinc-300 bg-white dark:border-zinc-800 dark:bg-zinc-900">
+	      <div className="flex flex-wrap items-center justify-between gap-3 border-b border-zinc-200 px-4 py-3 dark:border-zinc-800">
+		<div>
+		  <h1 className="text-lg font-bold">{theatreTitle}</h1>
+		  <p className="text-sm text-zinc-500 dark:text-zinc-400">
+		    同接 {theatreInfo.watchingUsers.length} 人
+		  </p>
+		</div>
+
+		<div className="flex flex-wrap gap-2">
+		  <div className="hidden flex-wrap gap-2 md:flex">
+		    {(Object.keys (LAYOUT_LABELS) as TheatreLayoutMode[]).map (mode => (
+			<Button
+			    key={mode}
+			    type="button"
+			    size="sm"
+			    variant={layoutMode === mode ? 'default' : 'outline'}
+			    onClick={() => changeLayoutMode (mode)}>
+			  {LAYOUT_LABELS[mode]}
+			</Button>))}
+		  </div>
+
+		  <Button
+		      type="button"
+		      size="sm"
+		      variant={skipVote.voted ? 'secondary' : 'destructive'}
+		      disabled={loading || !(post)}
+		      onClick={handleSkipVote}>
+		    {skipVote.voted ? 'スキップ取消' : 'スキップ'}
+		    {` ${ skipVote.votesCount } / ${ skipVote.requiredCount }`}
+		  </Button>
+
+		</div>
+	      </div>
+
+	      <div className="flex justify-center bg-black">
+		{post ? (
+		    <PostEmbed
+			key={post.id}
+			ref={embedRef}
+			post={post}
+			onLoadComplete={info => {
+			  embedRef.current?.play ()
+			  setVideoLength (info.lengthInSeconds * 1_000)
+			}}
+			onMetadataChange={syncPlayback}
+			onError={handlePlaybackError}/>) : (
+		    <div className="grid min-h-72 place-items-center text-zinc-400">
+		      {loading ? '次の投稿を選んでゐます……' : '上映待機中'}
+		    </div>)}
+	      </div>
+
+	      <div className="flex flex-wrap items-center justify-between gap-3 px-4 py-3">
+		<div className="min-w-0">
+		  <div className="text-xs font-bold text-zinc-500 dark:text-zinc-400">
+		    再生中
+		  </div>
+		  {post ? (
+		      <PrefetchLink to={`/posts/${ post.id }`} className="font-bold hover:underline">
+			{post.title || post.url}
+		      </PrefetchLink>) : (
+		      <span className="text-zinc-500">未選択</span>)}
+		</div>
+
+		<Button
+		    type="button"
+		    size="sm"
+		    variant="outline"
+		    disabled={!(post)}
+		    onClick={() => post && setEditingPost (post)}>
+		  この投稿を編集
+		</Button>
+	      </div>
+		    </section>
+
+	    {editingPost && (
+		<section className="rounded border border-amber-300 bg-amber-50 p-4 dark:border-amber-800 dark:bg-amber-950/30">
+		  <div className="mb-3 flex flex-wrap items-start justify-between gap-3">
+		    <div>
+		      <h2 className="font-bold">編集中の投稿</h2>
+		      <p className="text-sm text-amber-900 dark:text-amber-100">
+			上映が次へ進んでも、このフォームは
+			<PrefetchLink
+			    to={`/posts/${ editingPost.id }`}
+			    className="mx-1 font-bold underline">
+			  {editingPost.title || editingPost.url}
+			</PrefetchLink>
+			に固定されます。
+		      </p>
+		    </div>
+
+		    <Button type="button" variant="outline" size="sm" onClick={() => setEditingPost (null)}>
+		      閉じる
+		    </Button>
+		  </div>
+
+		  <PostEditForm
+		      post={editingPost}
+		      onSave={newPost => {
+			setEditingPost (newPost)
+			if (post?.id === newPost.id)
+			  setPost (newPost)
+			void refreshWeights ()
+		      }}/>
+		</section>)}
 
 	    <div className="md:hidden">
-	  {post && <TagDetailSidebar post={post} sp/>}
+	      {commentsPanel}
 	    </div>
-      </div>)
+
+	    {layoutMode === 'commentsBottom' && (
+		<div className="hidden md:block">
+		  {commentsPanel}
+		</div>)}
+
+	    <div className="md:hidden">
+	      {tagPanel}
+	    </div>
+
+	    {layoutMode === 'tagsBottom' && (
+		<div className="hidden md:block">
+		  {tagPanel}
+		</div>)}
+
+	    {historyPanel}
+	    {weightsPanel}
+
+	    <div className="md:hidden">
+	      {participantsPanel}
+	    </div>
+
+	    {layoutMode === 'commentsBottom' && (
+		<div className="hidden md:block">
+		  {participantsPanel}
+		</div>)}
+	    </div>
+	  </motion.main>
+
+	  {layoutMode !== 'commentsBottom' && (
+	      <motion.aside
+		  layout="position"
+		  className="hidden min-w-0 space-y-4 md:order-none md:block md:overflow-y-auto">
+		{commentsPanel}
+		{participantsPanel}
+	      </motion.aside>)}
+	</div>
+      </motion.div>)
 }
 
 
+const WeightRows: FC<{ rows: TheatrePostSelectionWeights['lightestPosts'] }> = ({ rows }) => (
+    <div className="space-y-2 text-sm">
+      {rows.length === 0 ? (
+	  <div className="text-zinc-500">候補はありません。</div>) : rows.slice (0, 8).map (row => (
+	  <div key={row.post.id} className="border-t border-zinc-100 pt-2 first:border-t-0 first:pt-0 dark:border-zinc-800">
+	    <PrefetchLink to={`/posts/${ row.post.id }`} className="line-clamp-1 font-bold hover:underline">
+	      {row.post.title || row.post.url}
+	    </PrefetchLink>
+	    <div className="flex justify-between gap-2 text-xs text-zinc-500">
+	      <span>penalty {row.penalty}</span>
+	      <span>weight {row.weight.toFixed (3)}</span>
+	    </div>
+	  </div>))}
+    </div>)
+
+
 export default TheatreDetailPage

frontend/src/types.ts

@@ -226,7 +226,7 @@ export type Theatre = {
 export type TheatreComment =
     | { theatreId:  number
 	no:         number
-	deteled:    false
+	deleted:    false
 	user:       { id: number, name: string } | null
 	content:    string
 	createdAt:  string }
@@ -234,7 +234,7 @@ export type TheatreComment =
 	no:         number
 	deleted:    true
 	user:       { id: number, name: string } | null
-	content     null,
+	content:    null,
 	createdAt:  string }
 
 export type TheatreProgramme = {
@@ -243,6 +243,46 @@ export type TheatreProgramme = {
     post:       Post
     createdAt:  string }
 
+export type TheatreSkipVoteStatus = {
+    votesCount:          number
+    requiredCount:       number
+    watchingUsersCount:  number
+    voted:               boolean }
+
+export type TheatreInfo = {
+    hostFlg:        boolean
+    postId:         number | null
+    postStartedAt:  string | null
+    postElapsedMs:  number | null
+    watchingUsers:  Pick<User, 'id' | 'name'>[]
+    skipVote:       TheatreSkipVoteStatus
+    skipped?:       boolean }
+
+export type TheatreSkipEvent = {
+    id:                 number
+    theatreId:          number
+    post:               Post
+    skippedByUser:      Pick<User, 'id' | 'name'>
+    voters:             Pick<User, 'id' | 'name'>[]
+    tags:               Tag[]
+    programmePosition:  number | null
+    createdAt:          string }
+
+export type TheatrePostWeight = {
+    post:     Post
+    weight:   number
+    penalty:  number
+    tags:     Tag[] }
+
+export type TheatreTagPenalty = {
+    tag:      Tag
+    penalty:  number }
+
+export type TheatrePostSelectionWeights = {
+    tagPenalties:  TheatreTagPenalty[]
+    lightestPosts: TheatrePostWeight[]
+    heaviestPosts: TheatrePostWeight[] }
+
 export type User = {
     id:               number
     name:             string | null