グカネータ / 質問パターン見直し (#41) (#365)

Reviewed-on: #365 Co-authored-by: miteruzo <miteruzo@naver.com> Co-committed-by: miteruzo <miteruzo@naver.com>
2026-06-12 01:35:31 +09:00
@@ -27,26 +27,20 @@ class GekanatorGamesController < ApplicationController
    game = GekanatorGame.find_by(id: params[:id])
    return head :not_found unless game

-    asked_ids = Array(game.answers).filter_map { |answer| answer_question_id(answer) }
-    existing_example_ids =
-        GekanatorQuestionExample.where(post_id: game.correct_post_id)
-                                .select(:gekanator_question_id)
-    # Direct examples only for now; post_similarity-based expansion is deferred.
    questions =
        GekanatorQuestion
        .accepted
+        .includes(:gekanator_question_examples)
        .where(kind: 'post_similarity', source: 'user_suggested')
-        .where.not(id: existing_example_ids)
-        .order(priority_weight: :desc, id: :asc)
+        .to_a
+
+    selected = weighted_sample_questions(
+        questions,
+        post_id: game.correct_post_id,
+        limit: 2)

    render json: {
-      questions: questions.filter_map { |question|
-        json = extra_question_json(question)
-        next if asked_ids.include?(json[:id].to_s)
-        next if asked_ids.include?("post-similarity:#{ json[:id] }")
-
-        json
-      }.first(2)
+      questions: selected.map { |question| extra_question_json(question) }
    }
  end

@@ -84,11 +78,10 @@ class GekanatorGamesController < ApplicationController
                gekanator_question: question,
                post: game.correct_post,
                user: current_user)
-        example.assign_attributes(
-            gekanator_game: game,
+        example.record_answer!(
            answer: item[:answer],
            source: 'post_game_extra',
-            weight: 1.0)
+            gekanator_game: game)
        example.save!
      end
    end
@@ -107,12 +100,41 @@ class GekanatorGamesController < ApplicationController
    }
  end

-  def answer_question_id answer
-    value = if answer.is_a?(Hash)
-      answer['question_id'].presence || answer[:question_id].presence ||
-        answer['questionId'].presence || answer[:questionId].presence
+  def weighted_sample_questions questions, post_id:, limit:
+    remaining = questions.uniq(&:id)
+    selected = []
+
+    while selected.length < limit && remaining.any?
+      weighted =
+          remaining.map { |question|
+            [question, selection_weight_for(question, post_id: post_id)]
+          }
+      total_weight = weighted.sum { |_question, weight| weight }
+      break if total_weight <= 0
+
+      target = rand * total_weight
+      cumulative = 0.0
+      chosen =
+          weighted.find do |_question, weight|
+            cumulative += weight
+            cumulative >= target
+          end&.first || weighted.first.first
+
+      selected << chosen
+      remaining.reject! { |question| question.id == chosen.id }
    end

-    value&.to_s
+    selected
+  end
+
+  def selection_weight_for question, post_id:
+    sample_count =
+        question.gekanator_question_examples.sum { |example|
+          next 0 unless example.post_id == post_id
+
+          example.sample_count.presence || 1
+        }
+
+    question.priority_weight.to_f / (1.0 + sample_count * 0.15)
  end
 end
@@ -1,5 +1,6 @@
 class GekanatorQuestionExample < ApplicationRecord
  ANSWERS = GekanatorQuestionSuggestion::ANSWERS
+  NON_UNKNOWN_ANSWERS = ANSWERS - ['unknown']
  SOURCES = ['initial_suggestion', 'post_game_extra'].freeze

  belongs_to :gekanator_question
@@ -8,10 +9,89 @@ class GekanatorQuestionExample < ApplicationRecord
  belongs_to :gekanator_game, optional: true

  validates :answer, presence: true, inclusion: { in: ANSWERS }
+  validates :answer_counts, presence: true
+  validates :sample_count,
+            presence: true,
+            numericality: {
+              only_integer: true,
+              greater_than: 0
+            }
  validates :source, presence: true, inclusion: { in: SOURCES }
  validates :weight,
            presence: true,
            numericality: {
              greater_than: 0
            }
+
+  before_validation :normalize_learning_state
+
+  def record_answer!(answer:, source:, gekanator_game: nil)
+    answer = answer.to_s
+    raise ArgumentError, 'invalid answer' unless ANSWERS.include?(answer)
+
+    counts = normalized_answer_counts
+    counts[answer] += 1
+
+    self.answer_counts = counts
+    self.sample_count = counts.values.sum
+    self.gekanator_game = gekanator_game if gekanator_game.present?
+    self.source = source if new_record?
+
+    apply_aggregated_answer!(preferred_answer: answer)
+    self
+  end
+
+  private
+
+  def normalize_learning_state
+    counts = normalized_answer_counts
+
+    if counts.values.sum.zero? && answer.present?
+      counts[answer] = 1
+    end
+
+    self.answer_counts = counts
+    self.sample_count = counts.values.sum
+
+    apply_aggregated_answer!
+  end
+
+  def apply_aggregated_answer!(preferred_answer: nil)
+    counts = normalized_answer_counts
+    known_counts = counts.slice(*NON_UNKNOWN_ANSWERS)
+    known_total = known_counts.values.sum
+
+    if known_total.zero?
+      self.answer = 'unknown'
+      self.weight = 0.1
+      return
+    else
+      max_count = known_counts.values.max
+      candidates = known_counts.select { |_answer, count| count == max_count }.keys
+      self.answer =
+          if preferred_answer.present? && candidates.include?(preferred_answer)
+            preferred_answer
+          elsif answer.present? && candidates.include?(answer)
+            answer
+          else
+            candidates.first
+          end
+    end
+
+    consensus = max_count.to_f / known_total
+    self.weight = Math.sqrt(known_total) * consensus
+  end
+
+  def normalized_answer_counts
+    base = ANSWERS.index_with(0)
+
+    answer_counts.to_h.each do |key, value|
+      answer_key = key.to_s
+      next unless ANSWERS.include?(answer_key)
+
+      base[answer_key] = value.to_i
+    end
+
+    base
+  end
 end
@@ -26,13 +26,16 @@ module Gekanator
            },
            gekanator_question_suggestion: suggestion,
            created_by: user)
-        GekanatorQuestionExample.create!(
+        example =
+            GekanatorQuestionExample.new(
                gekanator_question: question,
                post: suggestion.gekanator_game.correct_post,
-            user: user,
-            gekanator_game: suggestion.gekanator_game,
+                user: user)
+        example.record_answer!(
            answer: suggestion.answer,
-            source: 'initial_suggestion')
+            source: 'initial_suggestion',
+            gekanator_game: suggestion.gekanator_game)
+        example.save!
        suggestion.update!(processed: true)
        question
      end
@@ -0,0 +1,40 @@
+class AddAnswerStatisticsToGekanatorQuestionExamples < ActiveRecord::Migration[8.0]
+  class MigrationGekanatorQuestionExample < ApplicationRecord
+    self.table_name = 'gekanator_question_examples'
+  end
+
+  def up
+    add_column :gekanator_question_examples,
+               :answer_counts,
+               :json,
+               null: true
+    add_column :gekanator_question_examples,
+               :sample_count,
+               :integer,
+               null: false,
+               default: 1
+
+    MigrationGekanatorQuestionExample.reset_column_information
+    MigrationGekanatorQuestionExample.find_each do |example|
+      counts = {
+        'yes' => 0,
+        'no' => 0,
+        'partial' => 0,
+        'probably_no' => 0,
+        'unknown' => 0
+      }
+      counts[example.answer] = 1 if counts.key?(example.answer)
+
+      example.update_columns(
+        answer_counts: counts,
+        sample_count: 1)
+    end
+
+    change_column_null :gekanator_question_examples, :answer_counts, false
+  end
+
+  def down
+    remove_column :gekanator_question_examples, :sample_count
+    remove_column :gekanator_question_examples, :answer_counts
+  end
+end
@@ -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_06_10_000000) do
+ActiveRecord::Schema[8.0].define(version: 2026_06_12_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
@@ -85,6 +85,8 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_10_000000) do
    t.float "weight", default: 1.0, null: false
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
+    t.json "answer_counts", null: false
+    t.integer "sample_count", default: 1, null: false
    t.index ["gekanator_game_id"], name: "index_gekanator_question_examples_on_gekanator_game_id"
    t.index ["gekanator_question_id", "post_id", "user_id"], name: "idx_gekanator_question_examples_on_question_post_user", unique: true
    t.index ["gekanator_question_id"], name: "index_gekanator_question_examples_on_gekanator_question_id"
@@ -275,7 +275,7 @@ RSpec.describe 'Gekanator learning API', type: :request do
  end

  describe 'GET /gekanator/games/:id/extra_questions' do
-    it 'returns at most two accepted user_suggested post_similarity questions' do
+    it 'returns at most two accepted user_suggested post_similarity questions without duplicates' do
      sign_in_as admin

      low = create_post_similarity_question!(
@@ -295,15 +295,14 @@ RSpec.describe 'Gekanator learning API', type: :request do

      expect(response).to have_http_status(:ok)
      expect(json['questions'].length).to eq(2)
-      expect(json['questions'].map { _1['id'] }).to eq([high.id, middle.id])
-      expect(json['questions'].map { _1['id'] }).not_to include(low.id)
+      expect(json['questions'].map { _1['id'] }.uniq.length).to eq(2)
+      expect(json['questions'].map { _1['id'] }).to all(be_in([low.id, high.id, middle.id]))
    end

-    it 'does not return questions that already have an example for the correct post' do
+    it 'can return questions that already have an example for the correct post' do
      sign_in_as admin

      existing = create_post_similarity_question!(text: 'already learned?')
-      fresh = create_post_similarity_question!(text: 'fresh?')

      GekanatorQuestionExample.create!(
        gekanator_question: existing,
@@ -317,15 +316,13 @@ RSpec.describe 'Gekanator learning API', type: :request do
      get "/gekanator/games/#{game.id}/extra_questions"

      expect(response).to have_http_status(:ok)
-      expect(json['questions'].map { _1['id'] }).to include(fresh.id)
-      expect(json['questions'].map { _1['id'] }).not_to include(existing.id)
+      expect(json['questions'].map { _1['id'] }).to include(existing.id)
    end

-    it 'does not return questions already asked in the game using snake_case question_id' do
+    it 'can return questions already asked in the game using snake_case question_id' do
      sign_in_as admin

      asked = create_post_similarity_question!(text: 'already asked?')
-      fresh = create_post_similarity_question!(text: 'fresh?')
      game.update!(
        answers: [
          {
@@ -338,15 +335,13 @@ RSpec.describe 'Gekanator learning API', type: :request do
      get "/gekanator/games/#{game.id}/extra_questions"

      expect(response).to have_http_status(:ok)
-      expect(json['questions'].map { _1['id'] }).to include(fresh.id)
-      expect(json['questions'].map { _1['id'] }).not_to include(asked.id)
+      expect(json['questions'].map { _1['id'] }).to include(asked.id)
    end

-    it 'does not return questions already asked in the game using camelCase questionId' do
+    it 'can return questions already asked in the game using camelCase questionId' do
      sign_in_as admin

      asked = create_post_similarity_question!(text: 'already asked?')
-      fresh = create_post_similarity_question!(text: 'fresh?')
      game.update!(
        answers: [
          {
@@ -359,8 +354,7 @@ RSpec.describe 'Gekanator learning API', type: :request do
      get "/gekanator/games/#{game.id}/extra_questions"

      expect(response).to have_http_status(:ok)
-      expect(json['questions'].map { _1['id'] }).to include(fresh.id)
-      expect(json['questions'].map { _1['id'] }).not_to include(asked.id)
+      expect(json['questions'].map { _1['id'] }).to include(asked.id)
    end

    it 'does not return non-accepted, non-user_suggested, or non-post_similarity questions' do
@@ -584,5 +578,35 @@ RSpec.describe 'Gekanator learning API', type: :request do
        other_post.id.to_s => 'no'
      )
    end
+
+    it 'normalizes legacy title length questions' do
+      sign_in_as admin
+
+      GekanatorQuestion.create!(
+        text: '題名が長めの投稿?',
+        kind: 'title',
+        source: 'admin_curated',
+        status: 'accepted',
+        priority_weight: 1.0,
+        condition: {
+          type: 'title-length-greater-than',
+          length: 20
+        },
+        created_by: admin
+      )
+
+      get '/gekanator/questions'
+
+      expect(response).to have_http_status(:ok)
+      question_json = json['questions'].find { _1['id'] == 'title:length-at-least:21' }
+      expect(question_json).to include(
+        'text' => 'タイトルは 21 文字以上?',
+        'kind' => 'title'
+      )
+      expect(question_json['condition']).to include(
+        'type' => 'title-length-at-least',
+        'length' => 21
+      )
+    end
  end
 end
@@ -2,6 +2,7 @@ import { beforeEach, describe, expect, it, vi } from 'vitest'

 import { apiPost } from '@/lib/api'
 import {
+  buildGekanatorQuestions,
  expectedAnswerForQuestion,
  restoreGekanatorQuestion,
  saveGekanatorExtraQuestionAnswers,
@@ -146,6 +147,23 @@ describe('expectedAnswerForQuestion', () => {

    expect(expectedAnswerForQuestion(question, post({ tags: [] }))).toBe('no')
  })
+
+  it('ignores example answers for direct title facts', () => {
+    const question: StoredGekanatorQuestion = {
+      id: 'title:length-at-least:20',
+      text: 'タイトルは 20 文字以上?',
+      kind: 'title',
+      condition: {
+        type: 'title-length-at-least',
+        length: 20,
+      },
+      exampleAnswers: {
+        1: 'yes',
+      },
+    }
+
+    expect(expectedAnswerForQuestion(question, post({ id: 1, title: 'short' }))).toBe('no')
+  })
 })

 describe('restoreGekanatorQuestion', () => {
@@ -187,6 +205,65 @@ describe('restoreGekanatorQuestion', () => {
    expect(question.test(post({ id: 2 }))).toBe(false)
    expect(question.test(post({ id: 3 }))).toBe(false)
  })
+
+  it('tests a post_similarity question against its configured partial answer', () => {
+    const question = restoreGekanatorQuestion({
+      id: 'post-similarity:10',
+      text: '喜多ちゃんが泣いてる?',
+      kind: 'post_similarity',
+      source: 'user_suggested',
+      priorityWeight: 1.2,
+      condition: {
+        type: 'post-similarity',
+        postId: 999,
+        answer: 'partial',
+        threshold: 0.65,
+      },
+      exampleAnswers: {
+        1: 'partial',
+        2: 'yes',
+      },
+    })
+
+    expect(question.test(post({ id: 1 }))).toBe(true)
+    expect(question.test(post({ id: 2 }))).toBe(false)
+  })
+
+  it('normalizes legacy title-length-greater-than questions', () => {
+    const question = restoreGekanatorQuestion({
+      id: 'title:length-greater-than:20',
+      text: '題名が長めの投稿?',
+      kind: 'title',
+      condition: {
+        type: 'title-length-greater-than',
+        length: 20,
+      },
+    })
+
+    expect(question.id).toBe('title:length-at-least:21')
+    expect(question.condition).toEqual({
+      type: 'title-length-at-least',
+      length: 21,
+    })
+    expect(question.test(post({ title: 'x'.repeat(20) }))).toBe(false)
+    expect(question.test(post({ title: 'x'.repeat(21) }))).toBe(true)
+  })
+})
+
+describe('buildGekanatorQuestions', () => {
+  it('builds quantitative title length questions', () => {
+    const questions = buildGekanatorQuestions([
+      post({ id: 1, title: 'a' }),
+      post({ id: 2, title: 'bb' }),
+      post({ id: 3, title: 'ccc' }),
+      post({ id: 4, title: 'dddd' }),
+    ])
+    const titleQuestion = questions.find(question =>
+      question.condition.type === 'title-length-at-least')
+
+    expect(titleQuestion?.text).toMatch(/^タイトルは \d+ 文字以上\?$/)
+    expect(titleQuestion?.id).toMatch(/^title:length-at-least:\d+$/)
+  })
 })

 describe('Gekanator API writers', () => {
@@ -373,9 +373,11 @@ export const fetchGekanatorQuestions = async (): Promise<StoredGekanatorQuestion

 export const fetchGekanatorExtraQuestions = async (
    gameId:  number,
+    nonce?: string,
 ): Promise<GekanatorExtraQuestion[]> => {
  const data = await apiGet<{ questions: GekanatorExtraQuestion[] }> (
-      `/gekanator/games/${ gameId }/extra_questions`)
+      `/gekanator/games/${ gameId }/extra_questions`,
+      { params: nonce ? { nonce } : undefined })
  return data.questions
 }

@@ -0,0 +1,151 @@
+import { describe, expect, it } from 'vitest'
+
+import {
+    candidatePostsFor,
+    hardFilteredPostsForAnswer,
+    recoverCandidatePosts,
+} from '@/lib/gekanatorCandidateRecovery'
+
+import type {
+    GekanatorAnswerLog,
+    GekanatorAnswerValue,
+    GekanatorQuestion,
+} from '@/lib/gekanator'
+import type { Post } from '@/types'
+
+
+const post = (id: number): Post => ({
+  id,
+  versionNo: 1,
+  url: `https://example.com/posts/${ id }`,
+  title: `post ${ id }`,
+  thumbnail: null,
+  thumbnailBase: null,
+  tags: [],
+  viewed: false,
+  related: [],
+  originalCreatedFrom: null,
+  originalCreatedBefore: null,
+  createdAt: '2026-06-10T00:00:00.000Z',
+  updatedAt: '2026-06-10T00:00:00.000Z',
+  uploadedUser: null,
+})
+
+
+const postSimilarityQuestion = (
+    id:       string,
+    answers:  Record<`${ number }`, GekanatorAnswerValue>,
+): GekanatorQuestion => ({
+  id,
+  text: `${ id }?`,
+  kind: 'post_similarity',
+  condition: {
+      type: 'post-similarity',
+      postId: 9999,
+      answer: 'yes',
+      threshold: 0.65 },
+  source: 'user_suggested',
+  priorityWeight: 1,
+  exampleAnswers: answers,
+  test: candidate => answers[String (candidate.id) as `${ number }`] === 'yes',
+})
+
+
+const answer = (
+    question:  GekanatorQuestion,
+    value:     GekanatorAnswerValue,
+): GekanatorAnswerLog => ({
+  questionId: question.id,
+  questionText: question.text,
+  questionCondition: question.condition,
+  answer: value,
+  originalAnswer: value,
+})
+
+
+describe('candidatePostsFor', () => {
+  it('lets recovered candidates ignore old answers but not later answers', () => {
+    const posts = [post (1), post (2), post (3)]
+    const oldQuestion = postSimilarityQuestion ('old', {
+	1: 'no',
+	2: 'yes',
+	3: 'yes',
+    })
+    const laterQuestion = postSimilarityQuestion ('later', {
+	1: 'no',
+	2: 'no',
+	3: 'yes',
+    })
+
+    const candidates = candidatePostsFor ({
+	posts,
+	questions: [oldQuestion, laterQuestion],
+	answers: [answer (oldQuestion, 'yes'), answer (laterQuestion, 'yes')],
+	softenedQuestionIds: new Set (),
+	rejectedPostIds: new Set (),
+	recoveredCandidatePosts: new Map ([
+	    [1, 1],
+	    [3, 1],
+	]) })
+
+    expect(candidates.map (candidate => candidate.id)).toEqual ([3])
+  })
+
+  it('does not let recovered candidates bypass explicit rejected posts', () => {
+    const posts = [post (1), post (2)]
+    const question = postSimilarityQuestion ('question', {
+	1: 'yes',
+	2: 'yes',
+    })
+
+    const candidates = candidatePostsFor ({
+	posts,
+	questions: [question],
+	answers: [answer (question, 'yes')],
+	softenedQuestionIds: new Set (),
+	rejectedPostIds: new Set ([1]),
+	recoveredCandidatePosts: new Map ([[1, 1]]) })
+
+    expect(candidates.map (candidate => candidate.id)).toEqual ([2])
+  })
+})
+
+
+describe('hardFilteredPostsForAnswer', () => {
+  it('returns zero candidates without falling back to the original pool', () => {
+    const posts = [post (1), post (2)]
+    const question = postSimilarityQuestion ('question', {
+	1: 'yes',
+	2: 'yes',
+    })
+
+    expect(hardFilteredPostsForAnswer ({
+	posts,
+	question,
+	answer: 'no',
+    })).toEqual ([])
+  })
+})
+
+
+describe('recoverCandidatePosts', () => {
+  it('recovers high-score non-rejected, non-eligible candidates in staged batches', () => {
+    const posts = Array.from ({ length: 10 }, (_value, index) => post (index + 1))
+    const scores = new Map (posts.map (candidate => [candidate.id, candidate.id]))
+
+    const recovered = recoverCandidatePosts ({
+	posts,
+	scores,
+	rejectedPostIds: new Set ([10]),
+	recoveredCandidatePosts: new Map ([[8, 1]]),
+	eligiblePostIds: new Set ([9]),
+	answerCountAtRecovery: 2,
+	recoveryStepCount: 0,
+    })
+
+    expect(recovered?.recoveryStepCount).toBe (1)
+    expect([...(recovered?.recoveredCandidatePosts.keys () ?? [])])
+      .toEqual ([8, 7, 6, 5, 4, 3, 2])
+    expect(recovered?.recoveredCandidatePosts.get (7)).toBe (2)
+  })
+})
@@ -0,0 +1,146 @@
+import { expectedAnswerForQuestion } from '@/lib/gekanator'
+
+import type {
+    GekanatorAnswerLog,
+    GekanatorAnswerValue,
+    GekanatorQuestion,
+} from '@/lib/gekanator'
+import type { Post } from '@/types'
+
+
+export type RecoveredCandidatePost = {
+    postId:                number
+    answerCountAtRecovery: number }
+
+
+export const candidatePostsFor = ({
+    posts,
+    questions,
+    answers,
+    softenedQuestionIds,
+    rejectedPostIds,
+    recoveredCandidatePosts,
+}: {
+    posts:                   Post[]
+    questions:               GekanatorQuestion[]
+    answers:                 GekanatorAnswerLog[]
+    softenedQuestionIds:     Set<string>
+    rejectedPostIds:         Set<number>
+    recoveredCandidatePosts: Map<number, number>
+}): Post[] => {
+  const questionById = new Map (questions.map (question => [question.id, question]))
+
+  return posts.filter (post => {
+    if (rejectedPostIds.has (post.id))
+      return false
+
+    const answerCountAtRecovery = recoveredCandidatePosts.get (post.id)
+
+    return answers.every ((answer, index) => {
+      if (answerCountAtRecovery !== undefined && index < answerCountAtRecovery)
+	return true
+
+      if (softenedQuestionIds.has (answer.questionId))
+	return true
+
+      const question = questionById.get (answer.questionId)
+      if (!(question))
+	return true
+
+      switch (answer.answer)
+      {
+      case 'yes':
+      case 'no': {
+	const expected = expectedAnswerForQuestion (question, post)
+	return expected === null || expected === 'unknown' || expected === answer.answer
+      }
+      default:
+	return true
+      }
+    })
+  })
+}
+
+
+export const hardFilteredPostsForAnswer = ({
+    posts,
+    question,
+    answer,
+}: {
+    posts:     Post[]
+    question:  GekanatorQuestion
+    answer:    GekanatorAnswerValue
+}): Post[] => {
+  if (answer === 'unknown')
+    return posts
+
+  return posts.filter (post => {
+    const expected = expectedAnswerForQuestion (question, post)
+    return expected === null || expected === 'unknown' || expected === answer
+  })
+}
+
+
+const concreteAnswerOptions: GekanatorAnswerValue[] = [
+    'yes',
+    'no',
+    'partial',
+    'probably_no']
+
+
+export const allConcreteAnswerOptionsExhausted = (
+    posts:      Post[],
+    question:   GekanatorQuestion | null,
+): boolean => {
+  if (!(question))
+    return false
+
+  return concreteAnswerOptions.every (answer =>
+      hardFilteredPostsForAnswer ({ posts, question, answer }).length === 0)
+}
+
+
+const nextRecoveryBatchSize = (recoveryStepCount: number): number =>
+    6 * (2 ** recoveryStepCount)
+
+
+export const recoverCandidatePosts = ({
+    posts,
+    scores,
+    rejectedPostIds,
+    recoveredCandidatePosts,
+    eligiblePostIds,
+    answerCountAtRecovery,
+    recoveryStepCount,
+}: {
+    posts:                   Post[]
+    scores:                  Map<number, number>
+    rejectedPostIds:         Set<number>
+    recoveredCandidatePosts: Map<number, number>
+    eligiblePostIds:         Set<number>
+    answerCountAtRecovery:   number
+    recoveryStepCount:       number
+}): {
+    recoveredCandidatePosts: Map<number, number>
+    recoveryStepCount:       number
+} | null => {
+  const recovered = new Map (recoveredCandidatePosts)
+  const candidates = posts
+      .filter (post =>
+	  !(rejectedPostIds.has (post.id))
+	  && !(eligiblePostIds.has (post.id))
+	  && !(recovered.has (post.id)))
+      .sort ((a, b) =>
+	  (scores.get (b.id) ?? Number.NEGATIVE_INFINITY)
+	      - (scores.get (a.id) ?? Number.NEGATIVE_INFINITY))
+      .slice (0, nextRecoveryBatchSize (recoveryStepCount))
+
+  if (candidates.length === 0)
+    return null
+
+  candidates.forEach (post => recovered.set (post.id, answerCountAtRecovery))
+
+  return {
+      recoveredCandidatePosts: recovered,
+      recoveryStepCount: recoveryStepCount + 1 }
+}
@@ -0,0 +1,167 @@
+import { titleLengthMinimumForCondition } from '@/lib/gekanator'
+
+import type {
+    GekanatorAnswerLog,
+    GekanatorAnswerValue,
+    GekanatorQuestion,
+} from '@/lib/gekanator'
+
+
+export const monthForCondition = (
+    condition:  GekanatorQuestion['condition'],
+): number | null => {
+  if (condition.type === 'original-month')
+    return condition.month
+
+  if (condition.type !== 'original-month-day')
+    return null
+
+  const month = Number (condition.monthDay.split ('-')[0])
+  return Number.isInteger (month) ? month : null
+}
+
+
+const isTitleLengthContradiction = (
+    candidate:  GekanatorQuestion['condition'],
+    previous:   GekanatorQuestion['condition'],
+    answer:     GekanatorAnswerValue,
+): boolean => {
+  const candidateLength = titleLengthMinimumForCondition (candidate)
+  const previousLength = titleLengthMinimumForCondition (previous)
+  if (candidateLength === null || previousLength === null)
+    return false
+
+  switch (answer)
+  {
+  case 'yes':
+    return candidateLength <= previousLength
+  case 'no':
+    return candidateLength >= previousLength
+  default:
+    return false
+  }
+}
+
+
+const isQuestionRedundantAfterAnswers = (
+    question:  GekanatorQuestion,
+    answers:   GekanatorAnswerLog[],
+): boolean => answers.some (answer => {
+  const previous = answer.questionCondition
+  return previous !== undefined
+      && isTitleLengthContradiction (question.condition, previous, answer.answer)
+})
+
+
+const isSourceFactBlocked = (
+    candidate:  GekanatorQuestion['condition'],
+    previous:   GekanatorQuestion['condition'],
+    answer:     GekanatorAnswerValue,
+): boolean => {
+  if (candidate.type !== 'source' || previous.type !== 'source')
+    return false
+
+  switch (answer)
+  {
+  case 'yes':
+    return true
+  case 'no':
+    return candidate.host === previous.host
+  default:
+    return false
+  }
+}
+
+
+const isOriginalYearFactBlocked = (
+    candidate:  GekanatorQuestion['condition'],
+    previous:   GekanatorQuestion['condition'],
+    answer:     GekanatorAnswerValue,
+): boolean => {
+  if (candidate.type !== 'original-year' || previous.type !== 'original-year')
+    return false
+
+  switch (answer)
+  {
+  case 'yes':
+    return true
+  case 'no':
+    return candidate.year === previous.year
+  default:
+    return false
+  }
+}
+
+
+const isOriginalMonthFactBlocked = (
+    candidate:  GekanatorQuestion['condition'],
+    previous:   GekanatorQuestion['condition'],
+    answer:     GekanatorAnswerValue,
+): boolean => {
+  switch (answer)
+  {
+  case 'yes':
+    if (previous.type === 'original-month')
+      {
+	if (candidate.type === 'original-month')
+	  return true
+
+	if (candidate.type === 'original-month-day')
+	  return monthForCondition (candidate) !== previous.month
+
+	return false
+      }
+
+    if (previous.type === 'original-month-day')
+      return candidate.type === 'original-month'
+	  || candidate.type === 'original-month-day'
+
+    return false
+  case 'no':
+    if (previous.type === 'original-month')
+      {
+	if (candidate.type === 'original-month')
+	  return candidate.month === previous.month
+
+	if (candidate.type === 'original-month-day')
+	  return monthForCondition (candidate) === previous.month
+
+	return false
+      }
+
+    if (previous.type === 'original-month-day')
+      return candidate.type === 'original-month-day'
+	  && candidate.monthDay === previous.monthDay
+
+    return false
+  default:
+    return false
+  }
+}
+
+
+const isFactQuestionBlocked = (
+    candidate:  GekanatorQuestion['condition'],
+    previous:   GekanatorQuestion['condition'],
+    answer:     GekanatorAnswerValue,
+): boolean => {
+  if (!(answer === 'yes' || answer === 'no'))
+    return false
+
+  return isSourceFactBlocked (candidate, previous, answer)
+      || isOriginalYearFactBlocked (candidate, previous, answer)
+      || isOriginalMonthFactBlocked (candidate, previous, answer)
+}
+
+
+export const isQuestionHardFilteredAfterAnswers = (
+    question:  GekanatorQuestion,
+    answers:   GekanatorAnswerLog[],
+): boolean => answers.some (answer => {
+  const previous = answer.questionCondition
+  if (previous === undefined)
+    return false
+
+  return isQuestionRedundantAfterAnswers (question, [answer])
+      || isFactQuestionBlocked (question.condition, previous, answer.answer)
+})
@@ -12,8 +12,8 @@ export const gekanatorKeys = {
    root:      ['gekanator'] as const,
    posts:     () => ['gekanator', 'posts'] as const,
    questions: () => ['gekanator', 'questions'] as const,
-    extraQuestions: (gameId: number) =>
-		       ['gekanator', 'games', gameId, 'extra-questions'] as const }
+    extraQuestions: (gameId: number, nonce: string) =>
+		       ['gekanator', 'games', gameId, 'extra-questions', nonce] as const }

 export const tagsKeys = {
    root:         ['tags'] as const,
@@ -0,0 +1,154 @@
+import { describe, expect, it } from 'vitest'
+
+import { isQuestionHardFilteredAfterAnswers } from '@/lib/gekanatorQuestionFilters'
+
+import type {
+    GekanatorAnswerLog,
+    GekanatorAnswerValue,
+    GekanatorQuestion,
+    GekanatorQuestionCondition,
+} from '@/lib/gekanator'
+
+
+const question = (
+    condition:  GekanatorQuestionCondition,
+): GekanatorQuestion => ({
+  id: `${ condition.type }:candidate`,
+  text: 'candidate?',
+  kind: condition.type === 'source'
+      ? 'source'
+      : condition.type.startsWith ('original-')
+	? 'original_date'
+	: condition.type.startsWith ('title-')
+	  ? 'title'
+	  : 'tag',
+  condition,
+  source: 'default',
+  priorityWeight: 1,
+  test: () => false,
+})
+
+
+const answer = (
+    condition:  GekanatorQuestionCondition,
+    value:      GekanatorAnswerValue,
+): GekanatorAnswerLog => ({
+  questionId: 'previous',
+  questionText: 'previous?',
+  questionCondition: condition,
+  answer: value,
+  originalAnswer: value,
+})
+
+
+const blocked = (
+    candidate:  GekanatorQuestionCondition,
+    previous:   GekanatorQuestionCondition,
+    value:      GekanatorAnswerValue,
+): boolean =>
+    isQuestionHardFilteredAfterAnswers (question (candidate), [answer (previous, value)])
+
+
+describe('isQuestionHardFilteredAfterAnswers', () => {
+  it('blocks only contradictory or redundant month questions after a yes answer', () => {
+    const previous: GekanatorQuestionCondition = { type: 'original-month', month: 12 }
+
+    expect(blocked ({ type: 'original-month', month: 12 }, previous, 'yes')).toBe(true)
+    expect(blocked ({ type: 'original-month', month: 2 }, previous, 'yes')).toBe(true)
+    expect(blocked ({ type: 'original-month-day', monthDay: '2-14' }, previous, 'yes'))
+      .toBe(true)
+    expect(blocked ({ type: 'original-month-day', monthDay: '12-25' }, previous, 'yes'))
+      .toBe(false)
+    expect(blocked ({ type: 'original-year', year: 2024 }, previous, 'yes')).toBe(false)
+    expect(blocked ({ type: 'source', host: 'example.com' }, previous, 'yes')).toBe(false)
+    expect(blocked ({ type: 'tag', key: 'character:喜多郁代' }, previous, 'yes')).toBe(false)
+  })
+
+  it('blocks same-month facts after a no answer', () => {
+    const previous: GekanatorQuestionCondition = { type: 'original-month', month: 12 }
+
+    expect(blocked ({ type: 'original-month', month: 12 }, previous, 'no')).toBe(true)
+    expect(blocked ({ type: 'original-month', month: 2 }, previous, 'no')).toBe(false)
+    expect(blocked ({ type: 'original-month-day', monthDay: '12-25' }, previous, 'no'))
+      .toBe(true)
+    expect(blocked ({ type: 'original-month-day', monthDay: '2-14' }, previous, 'no'))
+      .toBe(false)
+  })
+
+  it('blocks all month and month-day questions after a month-day yes answer', () => {
+    const previous: GekanatorQuestionCondition = {
+      type: 'original-month-day',
+      monthDay: '12-25',
+    }
+
+    expect(blocked ({ type: 'original-month', month: 12 }, previous, 'yes')).toBe(true)
+    expect(blocked ({ type: 'original-month', month: 2 }, previous, 'yes')).toBe(true)
+    expect(blocked ({ type: 'original-month-day', monthDay: '12-25' }, previous, 'yes'))
+      .toBe(true)
+    expect(blocked ({ type: 'original-month-day', monthDay: '12-26' }, previous, 'yes'))
+      .toBe(true)
+  })
+
+  it('blocks the same month-day only after a month-day no answer', () => {
+    const previous: GekanatorQuestionCondition = {
+      type: 'original-month-day',
+      monthDay: '12-25',
+    }
+
+    expect(blocked ({ type: 'original-month-day', monthDay: '12-25' }, previous, 'no'))
+      .toBe(true)
+    expect(blocked ({ type: 'original-month-day', monthDay: '12-26' }, previous, 'no'))
+      .toBe(false)
+    expect(blocked ({ type: 'original-month', month: 12 }, previous, 'no')).toBe(false)
+  })
+
+  it('blocks year and source as single-value facts', () => {
+    expect(blocked (
+      { type: 'original-year', year: 2025 },
+      { type: 'original-year', year: 2024 },
+      'yes',
+    )).toBe(true)
+    expect(blocked (
+      { type: 'original-year', year: 2024 },
+      { type: 'original-year', year: 2024 },
+      'no',
+    )).toBe(true)
+    expect(blocked (
+      { type: 'source', host: 'b.example' },
+      { type: 'source', host: 'a.example' },
+      'yes',
+    )).toBe(true)
+    expect(blocked (
+      { type: 'source', host: 'b.example' },
+      { type: 'source', host: 'a.example' },
+      'no',
+    )).toBe(false)
+  })
+
+  it('does not hard-filter partial, probably_no, or unknown fact answers', () => {
+    const previous: GekanatorQuestionCondition = { type: 'original-month', month: 12 }
+    const candidate: GekanatorQuestionCondition = { type: 'original-month', month: 2 }
+
+    expect(blocked (candidate, previous, 'partial')).toBe(false)
+    expect(blocked (candidate, previous, 'probably_no')).toBe(false)
+    expect(blocked (candidate, previous, 'unknown')).toBe(false)
+  })
+
+  it('keeps title-length hard redundancy for yes and no only', () => {
+    const previous: GekanatorQuestionCondition = {
+      type: 'title-length-at-least',
+      length: 30,
+    }
+
+    expect(blocked ({ type: 'title-length-at-least', length: 20 }, previous, 'yes'))
+      .toBe(true)
+    expect(blocked ({ type: 'title-length-at-least', length: 40 }, previous, 'yes'))
+      .toBe(false)
+    expect(blocked ({ type: 'title-length-at-least', length: 40 }, previous, 'no'))
+      .toBe(true)
+    expect(blocked ({ type: 'title-length-at-least', length: 20 }, previous, 'no'))
+      .toBe(false)
+    expect(blocked ({ type: 'title-length-at-least', length: 20 }, previous, 'partial'))
+      .toBe(false)
+  })
+})
@@ -17,6 +17,12 @@ import { buildGekanatorQuestions,
 	 saveGekanatorQuestionSuggestion,
 	 storeGekanatorQuestion,
 	 titleLengthMinimumForCondition } from '@/lib/gekanator'
+import { allConcreteAnswerOptionsExhausted,
+	 candidatePostsFor,
+	 hardFilteredPostsForAnswer,
+	 recoverCandidatePosts } from '@/lib/gekanatorCandidateRecovery'
+import { isQuestionHardFilteredAfterAnswers,
+	 monthForCondition } from '@/lib/gekanatorQuestionFilters'
 import { gekanatorKeys } from '@/lib/queryKeys'
 import { cn } from '@/lib/utils'

@@ -28,6 +34,7 @@ import type { GekanatorAnswerLog,
 	      GekanatorQuestionCondition,
 	      GekanatorQuestion,
 	      StoredGekanatorQuestion } from '@/lib/gekanator'
+import type { RecoveredCandidatePost } from '@/lib/gekanatorCandidateRecovery'
 import type { Post } from '@/types'

 type Phase =
@@ -63,6 +70,8 @@ type GameSnapshot = {
    answers:                 GekanatorAnswerLog[]
    askedIds:                Set<string>
    softenedQuestionIds:     Set<string>
+    recoveredCandidatePosts: Map<number, number>
+    recoveryStepCount:       number
    askedQuestionBank:       GekanatorQuestion[]
    search:                  string
    selectingCorrectPost:    boolean
@@ -79,6 +88,8 @@ type StoredGekanatorGame = {
    answers:                     GekanatorAnswerLog[]
    askedIds:                    string[]
    softenedQuestionIds:         string[]
+    recoveredCandidatePosts?:    RecoveredCandidatePost[]
+    recoveryStepCount?:          number
    askedQuestionBank?:          StoredGekanatorQuestion[]
    askedQuestionBankIds?:       string[]
    search:                      string
@@ -178,6 +189,8 @@ const normalizeStoredGame = (game: StoredGekanatorGame): StoredGekanatorGame =>
  askedIds: game.askedIds.map (questionId => normalizeStoredQuestionId (questionId)),
  softenedQuestionIds: game.softenedQuestionIds.map (questionId =>
      normalizeStoredQuestionId (questionId)),
+  recoveredCandidatePosts: game.recoveredCandidatePosts ?? [],
+  recoveryStepCount: game.recoveryStepCount ?? 0,
  askedQuestionBank: game.askedQuestionBank?.map (question =>
      ({
 	  ...question,
@@ -280,6 +293,20 @@ const resettableExtraQuestionState = (): {
  extraQuestionState: 'idle' })


+const recoveredCandidateMapFromStored = (
+    items: RecoveredCandidatePost[],
+): Map<number, number> =>
+    new Map (items.map (item => [item.postId, item.answerCountAtRecovery]))
+
+
+const storedRecoveredCandidatesFromMap = (
+    recoveredCandidatePosts: Map<number, number>,
+): RecoveredCandidatePost[] =>
+    [...recoveredCandidatePosts.entries ()].map (([postId, answerCountAtRecovery]) => ({
+	postId,
+	answerCountAtRecovery }))
+
+
 const deltaFor = (matched: boolean, answer: GekanatorAnswerValue): number => {
  switch (answer)
  {
@@ -399,48 +426,6 @@ const recalculateScores = ({
 }


-const candidatePostsFor = ({
-    posts,
-    questions,
-    answers,
-    softenedQuestionIds,
-    rejectedPostIds,
-}: {
-    posts:                Post[]
-    questions:            GekanatorQuestion[]
-    answers:              GekanatorAnswerLog[]
-    softenedQuestionIds:  Set<string>
-    rejectedPostIds:      Set<number>
-}): Post[] => {
-  const questionById = new Map (questions.map (question => [question.id, question]))
-
-  return posts.filter (post => {
-    if (rejectedPostIds.has (post.id))
-      return false
-
-    return answers.every (answer => {
-      if (softenedQuestionIds.has (answer.questionId))
-	return true
-
-      const question = questionById.get (answer.questionId)
-      if (!(question))
-	return true
-
-      switch (answer.answer)
-      {
-      case 'yes':
-      case 'no': {
-	const expected = expectedAnswerForQuestion (question, post)
-	return expected === null || expected === 'unknown' || expected === answer.answer
-      }
-      default:
-	return true
-      }
-    })
-  })
-}
-
-
 const confidencesFor = (posts: Post[], scores: Map<number, number>): Confidence[] => {
  if (posts.length === 0)
    return []
@@ -489,17 +474,18 @@ const previewAnswer = ({
    question:  GekanatorQuestion
    answer:    GekanatorAnswerValue
 }): AnswerPreview => {
-  const hardFilteredPosts =
-      answer === 'unknown'
-	? posts
-	: posts.filter (post => {
-	    const expected = expectedAnswerForQuestion (question, post)
-	    return expected === null || expected === 'unknown' || expected === answer
-	  })
-  const nextPosts =
-      hardFilteredPosts.length > 0
-	? hardFilteredPosts
-	: posts
+  const nextPosts = hardFilteredPostsForAnswer ({
+      posts,
+      question,
+      answer })
+  if (nextPosts.length === 0)
+    return {
+	answer,
+	top: null,
+	candidateCount: 0,
+	effectiveCandidates: 0,
+	entropy: 0 }
+
  const nextScores = new Map (scores)
  nextPosts.forEach (post => {
    const expected = expectedAnswerForQuestion (question, post)
@@ -628,52 +614,6 @@ const sameConditionValue = (
 }


-const monthForCondition = (
-    condition:  GekanatorQuestion['condition'],
-): number | null => {
-  if (condition.type === 'original-month')
-    return condition.month
-
-  if (condition.type !== 'original-month-day')
-    return null
-
-  const month = Number (condition.monthDay.split ('-')[0])
-  return Number.isInteger (month) ? month : null
-}
-
-
-const isTitleLengthContradiction = (
-    candidate:  GekanatorQuestion['condition'],
-    previous:   GekanatorQuestion['condition'],
-    answer:     GekanatorAnswerValue,
-): boolean => {
-  const candidateLength = titleLengthMinimumForCondition (candidate)
-  const previousLength = titleLengthMinimumForCondition (previous)
-  if (candidateLength === null || previousLength === null)
-    return false
-
-  switch (answer)
-  {
-  case 'yes':
-    return candidateLength <= previousLength
-  case 'no':
-    return candidateLength >= previousLength
-  default:
-    return false
-  }
-}
-
-
-const isQuestionRedundantAfterAnswers = (
-    question:  GekanatorQuestion,
-    answers:   GekanatorAnswerLog[],
-): boolean => answers.some (answer => {
-  const previous = answer.questionCondition
-  return previous !== undefined
-      && isTitleLengthContradiction (question.condition, previous, answer.answer)
-})
-
-
 const isMonthCrossMatch = (
    candidate:  GekanatorQuestion['condition'],
    previous:   GekanatorQuestion['condition'],
@@ -808,7 +748,7 @@ const chooseQuestion = ({

    return questionsToRank
      .map (question => {
-	if (isQuestionRedundantAfterAnswers (question, answers))
+	if (isQuestionHardFilteredAfterAnswers (question, answers))
 	  return null

 	const signature = signatureFor (question, candidates)
@@ -934,6 +874,10 @@ const GekanatorPage: FC = () => {
      () => new Set (storedGame?.askedIds ?? []))
  const [softenedQuestionIds, setSoftenedQuestionIds] = useState<Set<string>> (
      () => new Set (storedGame?.softenedQuestionIds ?? []))
+  const [recoveredCandidatePosts, setRecoveredCandidatePosts] = useState<Map<number, number>> (
+      () => recoveredCandidateMapFromStored (storedGame?.recoveredCandidatePosts ?? []))
+  const [recoveryStepCount, setRecoveryStepCount] = useState (
+      storedGame?.recoveryStepCount ?? 0)
  const [askedQuestionBank, setAskedQuestionBank] = useState<GekanatorQuestion[]> (
      () => (storedGame?.askedQuestionBank ?? []).map (restoreGekanatorQuestion))
  const [storedAskedQuestionBankIds, setStoredAskedQuestionBankIds] = useState<string[]> (
@@ -1024,6 +968,8 @@ const GekanatorPage: FC = () => {
 	answers,
 	askedIds: [...askedIds],
 	softenedQuestionIds: [...softenedQuestionIds],
+	recoveredCandidatePosts: storedRecoveredCandidatesFromMap (recoveredCandidatePosts),
+	recoveryStepCount,
 	askedQuestionBank: askedQuestionBank.map (storeGekanatorQuestion),
 	askedQuestionBankIds: storedAskedQuestionBankIds,
 	search,
@@ -1059,6 +1005,8 @@ const GekanatorPage: FC = () => {
      answers,
      askedIds,
      softenedQuestionIds,
+      recoveredCandidatePosts,
+      recoveryStepCount,
      askedQuestionBank,
      storedAskedQuestionBankIds,
      search,
@@ -1086,8 +1034,10 @@ const GekanatorPage: FC = () => {
 	  questions: askedQuestionBank,
 	  answers,
 	  softenedQuestionIds,
-	  rejectedPostIds }),
-      [posts, askedQuestionBank, answers, softenedQuestionIds, rejectedPostIds])
+	  rejectedPostIds,
+	  recoveredCandidatePosts }),
+      [posts, askedQuestionBank, answers, softenedQuestionIds,
+	  rejectedPostIds, recoveredCandidatePosts])
  const questions = useMemo (
      () => mergeQuestions ([
 	  ...buildGekanatorQuestions (eligiblePosts.length > 1 ? eligiblePosts : posts),
@@ -1100,14 +1050,14 @@ const GekanatorPage: FC = () => {
      () => new Map (scoringQuestions.map (question => [question.id, question])),
      [scoringQuestions])
  const questionsSinceLastGuess = answers.length - lastGuessQuestionCount
-  const nonRejectedPosts = useMemo (
+  const availablePosts = useMemo (
      () => posts.filter (post => !(rejectedPostIds.has (post.id))),
      [posts, rejectedPostIds])
  const questionPosts =
      eligiblePosts.length > 1
 	|| questionsSinceLastGuess >= minQuestionsBeforeCertainGuess
 	  ? eligiblePosts
-	  : nonRejectedPosts
+	  : availablePosts
  const topScoredPosts = useMemo (
      () => eligiblePosts
      .map (post => ({ post, score: scores.get (post.id) ?? 0 }))
@@ -1133,7 +1083,7 @@ const GekanatorPage: FC = () => {
  const guessablePosts =
      eligiblePosts.length > 0
 	? eligiblePosts
-	: nonRejectedPosts
+	: availablePosts
  const guess = bestPost (guessablePosts, scores)
  const displayedGuess =
      posts.find (post => post.id === activeGuessId) ?? guess
@@ -1181,6 +1131,8 @@ const GekanatorPage: FC = () => {
    setAnswers ([])
    setAskedIds (new Set ())
    setSoftenedQuestionIds (new Set ())
+    setRecoveredCandidatePosts (new Map ())
+    setRecoveryStepCount (0)
    setAskedQuestionBank ([])
    setSearch ('')
    setSelectingCorrectPost (false)
@@ -1207,14 +1159,26 @@ const GekanatorPage: FC = () => {
      nextAskedQuestionBank,
      nextSoftenedQuestionIds,
      nextRejectedPostIds,
+      nextRecoveredCandidatePosts,
+      nextRecoveryStepCount,
+      allowPreQuestionRecovery,
  }: {
      nextAnswers:              GekanatorAnswerLog[]
      nextAskedIds:             Set<string>
      nextAskedQuestionBank:    GekanatorQuestion[]
      nextSoftenedQuestionIds:  Set<string>
      nextRejectedPostIds:      Set<number>
+      nextRecoveredCandidatePosts: Map<number, number>
+      nextRecoveryStepCount:    number
+      allowPreQuestionRecovery?: boolean
  }) => {
    let recoveredSoftenedQuestionIds = new Set (nextSoftenedQuestionIds)
+    let recoveredCandidatePosts = new Map (nextRecoveredCandidatePosts)
+    let recoveredStepCount = nextRecoveryStepCount
+    const answerCountAtRecovery =
+	allowPreQuestionRecovery
+	  ? nextAnswers.length
+	  : Math.max (nextAnswers.length - 1, 0)
    let recoveredScores = recalculateScores ({
 	posts,
 	questions: nextAskedQuestionBank,
@@ -1225,37 +1189,15 @@ const GekanatorPage: FC = () => {
 	questions: nextAskedQuestionBank,
 	answers: nextAnswers,
 	softenedQuestionIds: recoveredSoftenedQuestionIds,
-	rejectedPostIds: nextRejectedPostIds })
+	rejectedPostIds: nextRejectedPostIds,
+	recoveredCandidatePosts })
    let recoveredScoringQuestions = mergeQuestions ([
 	...buildGekanatorQuestions (
 	    recoveredEligiblePosts.length > 1 ? recoveredEligiblePosts : posts),
 	...acceptedQuestions,
 	...nextAskedQuestionBank])

-    while (
-	recoveredEligiblePosts.length === 0
-	|| (
-	    recoveredEligiblePosts.length !== 1
-	    && !(chooseQuestion ({
-		posts: recoveredEligiblePosts,
-		questions: recoveredScoringQuestions,
-		scores: recoveredScores,
-		answers: nextAnswers,
-		askedIds: nextAskedIds,
-		gameSeed })))
-    )
-      {
-	if (nextAnswers.length >= hardMaxQuestions)
-	  break
-
-	const softened = softenNextQuestionIds ({
-	    questions: nextAskedQuestionBank,
-	    answers: nextAnswers,
-	    softenedQuestionIds: recoveredSoftenedQuestionIds })
-	if (!(softened))
-	  break
-
-	recoveredSoftenedQuestionIds = softened
+    const refreshRecoveredState = () => {
      recoveredScores = recalculateScores ({
 	  posts,
 	  questions: nextAskedQuestionBank,
@@ -1266,7 +1208,8 @@ const GekanatorPage: FC = () => {
 	  questions: nextAskedQuestionBank,
 	  answers: nextAnswers,
 	  softenedQuestionIds: recoveredSoftenedQuestionIds,
-	    rejectedPostIds: nextRejectedPostIds })
+	  rejectedPostIds: nextRejectedPostIds,
+	  recoveredCandidatePosts })
      recoveredScoringQuestions = mergeQuestions ([
 	  ...buildGekanatorQuestions (
 	      recoveredEligiblePosts.length > 1 ? recoveredEligiblePosts : posts),
@@ -1274,8 +1217,61 @@ const GekanatorPage: FC = () => {
 	  ...nextAskedQuestionBank])
    }

+    const needsPreQuestionRecovery = () => {
+      if (!(allowPreQuestionRecovery) || recoveredEligiblePosts.length === 0)
+	return false
+
+      const nextQuestion = chooseQuestion ({
+	  posts: recoveredEligiblePosts,
+	  questions: recoveredScoringQuestions,
+	  scores: recoveredScores,
+	  answers: nextAnswers,
+	  askedIds: nextAskedIds,
+	  gameSeed })
+
+      return allConcreteAnswerOptionsExhausted (recoveredEligiblePosts, nextQuestion)
+    }
+
+    while (recoveredEligiblePosts.length === 0 || needsPreQuestionRecovery ())
+      {
+	const recoveredPosts = recoverCandidatePosts ({
+	    posts,
+	    scores: recoveredScores,
+	    rejectedPostIds: nextRejectedPostIds,
+	    recoveredCandidatePosts,
+	    eligiblePostIds: new Set (recoveredEligiblePosts.map (post => post.id)),
+	    answerCountAtRecovery,
+	    recoveryStepCount: recoveredStepCount })
+	if (recoveredPosts)
+	  {
+	    recoveredCandidatePosts = recoveredPosts.recoveredCandidatePosts
+	    recoveredStepCount = recoveredPosts.recoveryStepCount
+	    refreshRecoveredState ()
+	    if (recoveredEligiblePosts.length > 0 && !(needsPreQuestionRecovery ()))
+	      break
+	  }
+
+	if (
+	    recoveredEligiblePosts.length > 0
+	    || nextAnswers.length >= hardMaxQuestions
+	)
+	  break
+
+	const softened = softenNextQuestionIds ({
+	    questions: nextAskedQuestionBank,
+	    answers: nextAnswers,
+	    softenedQuestionIds: recoveredSoftenedQuestionIds })
+	if (!(softened))
+	  break
+
+	recoveredSoftenedQuestionIds = softened
+	refreshRecoveredState ()
+      }
+
    return {
 	softenedQuestionIds: recoveredSoftenedQuestionIds,
+	recoveredCandidatePosts,
+	recoveryStepCount: recoveredStepCount,
 	scores: recoveredScores,
 	eligiblePosts: recoveredEligiblePosts,
 	scoringQuestions: recoveredScoringQuestions }
@@ -1295,6 +1291,8 @@ const GekanatorPage: FC = () => {
 	answers: [...answers],
 	askedIds: new Set (askedIds),
 	softenedQuestionIds: new Set (softenedQuestionIds),
+	recoveredCandidatePosts: new Map (recoveredCandidatePosts),
+	recoveryStepCount,
 	askedQuestionBank: [...askedQuestionBank],
 	search,
 	selectingCorrectPost,
@@ -1319,21 +1317,26 @@ const GekanatorPage: FC = () => {
 	nextAskedIds,
 	nextAskedQuestionBank,
 	nextSoftenedQuestionIds: softenedQuestionIds,
-	nextRejectedPostIds: rejectedPostIds })
+	nextRejectedPostIds: rejectedPostIds,
+	nextRecoveredCandidatePosts: recoveredCandidatePosts,
+	nextRecoveryStepCount: recoveryStepCount })
    const nextSoftenedQuestionIds = recovered.softenedQuestionIds
+    const nextRecoveredCandidatePosts = recovered.recoveredCandidatePosts
    const nextScores = recovered.scores
    const nextEligiblePosts = recovered.eligiblePosts

    setScores (nextScores)
    setAskedIds (nextAskedIds)
    setSoftenedQuestionIds (nextSoftenedQuestionIds)
+    setRecoveredCandidatePosts (nextRecoveredCandidatePosts)
+    setRecoveryStepCount (recovered.recoveryStepCount)
    setAskedQuestionBank (nextAskedQuestionBank)
    setAnswers (nextAnswers)

    const nextGuessablePosts =
 	nextEligiblePosts.length > 0
 	  ? nextEligiblePosts
-	  : nonRejectedPosts
+	  : availablePosts
    const nextGuess = bestPost (nextGuessablePosts, nextScores)
    const nextQuestionCount = answers.length + 1
    const nextQuestionsSinceLastGuess =
@@ -1469,6 +1472,10 @@ const GekanatorPage: FC = () => {
      }

    setRejectedPostIds (new Set ([...rejectedPostIds, displayedGuess.id]))
+    setRecoveredCandidatePosts (
+	new Map (
+	    [...recoveredCandidatePosts.entries ()].filter (
+		([postId]) => postId !== displayedGuess.id)))
    setActiveGuessId (null)
    setSearch ('')
    setSelectingCorrectPost (false)
@@ -1486,6 +1493,8 @@ const GekanatorPage: FC = () => {
    setAnswers (snapshot.answers)
    setAskedIds (snapshot.askedIds)
    setSoftenedQuestionIds (snapshot.softenedQuestionIds)
+    setRecoveredCandidatePosts (snapshot.recoveredCandidatePosts)
+    setRecoveryStepCount (snapshot.recoveryStepCount)
    setAskedQuestionBank (snapshot.askedQuestionBank)
    setSearch (snapshot.search)
    setSelectingCorrectPost (snapshot.selectingCorrectPost)
@@ -1507,15 +1516,24 @@ const GekanatorPage: FC = () => {
 	nextAskedIds: askedIds,
 	nextAskedQuestionBank: askedQuestionBank,
 	nextSoftenedQuestionIds: softenedQuestionIds,
-	nextRejectedPostIds: rejectedPostIds })
+	nextRejectedPostIds: rejectedPostIds,
+	nextRecoveredCandidatePosts: recoveredCandidatePosts,
+	nextRecoveryStepCount: recoveryStepCount,
+	allowPreQuestionRecovery: true })

    setSoftenedQuestionIds (recovered.softenedQuestionIds)
+    setRecoveredCandidatePosts (recovered.recoveredCandidatePosts)
+    setRecoveryStepCount (recovered.recoveryStepCount)
    setScores (recovered.scores)

+    const recoveredGuessablePosts =
+	recovered.eligiblePosts.length > 0
+	  ? recovered.eligiblePosts
+	  : availablePosts
    const nextQuestion = chooseQuestion ({
 	posts: recovered.eligiblePosts.length > 1
 	    ? recovered.eligiblePosts
-	    : nonRejectedPosts,
+	    : availablePosts,
 	questions: recovered.scoringQuestions,
 	scores: recovered.scores,
 	answers,
@@ -1528,7 +1546,7 @@ const GekanatorPage: FC = () => {
 	return
      }

-    setActiveGuessId (guess?.id ?? null)
+    setActiveGuessId (bestPost (recoveredGuessablePosts, recovered.scores)?.id ?? null)
    setPhase ('guess')
  }

@@ -1582,12 +1600,13 @@ const GekanatorPage: FC = () => {
    setExtraQuestions ([])
    setExtraQuestionAnswers ({ })
    setPhase ('extra_questions')
+    const nonce = createGameSeed ()

    try
    {
      const questions = await queryClient.fetchQuery ({
-	  queryKey: gekanatorKeys.extraQuestions (gameId),
-	  queryFn: () => fetchGekanatorExtraQuestions (gameId) })
+	  queryKey: gekanatorKeys.extraQuestions (gameId, nonce),
+	  queryFn: () => fetchGekanatorExtraQuestions (gameId, nonce) })
      setExtraQuestions (questions)
      setExtraQuestionState (questions.length > 0 ? 'ready' : 'empty')
    }