#306

backend/app/controllers/materials_controller.rb

@@ -523,10 +523,7 @@ class MaterialsController < ApplicationController
         content_type: file.content_type,
     )
 
-    if file_sha256.present?
+    MaterialFileSha256.assign_metadata_sha256!(blob, file_sha256)
-      blob.metadata['sha256'] = file_sha256
-      blob.save! if blob.changed?
-    end
 
     blob
   ensure

backend/app/models/material.rb

@@ -1,6 +1,9 @@
 class Material < ApplicationRecord
   include MyDiscard
 
+  SOURCE_KINDS = ['uri', 'google_drive_path', 'google_drive_file',
+                  'legacy_drive_path'].freeze
+
   default_scope -> { kept }
 
   belongs_to :parent, class_name: 'Material', optional: true
@@ -20,7 +23,7 @@ class Material < ApplicationRecord
 
   validates :tag_id, uniqueness: true, allow_nil: true
   validates :source_kind,
-            inclusion: { in: MaterialSyncSuppression::SOURCE_KINDS },
+            inclusion: { in: SOURCE_KINDS },
             allow_blank: true
 
   validate :file_must_be_attached

backend/app/services/material_file_sha256.rb

@@ -1,16 +1,39 @@
 require 'digest'
+require 'json'
 
 class MaterialFileSha256
+  def self.blob_metadata blob
+    metadata = blob.metadata
+    return metadata if metadata.is_a?(Hash)
+    return { } if metadata.blank?
+
+    JSON.parse(metadata)
+  rescue JSON::ParserError
+    { }
+  end
+
+  def self.metadata_sha256 blob
+    blob_metadata(blob)['sha256'].presence
+  end
+
+  def self.assign_metadata_sha256! blob, sha256
+    return if sha256.blank?
+
+    metadata = blob_metadata(blob)
+    metadata['sha256'] = sha256
+    blob.metadata = metadata
+    blob.save! if blob.changed?
+  end
+
   def self.from_blob blob, allow_download: false
-    sha256 = blob.metadata['sha256']
+    sha256 = metadata_sha256(blob)
     return sha256 if sha256.present?
     return nil unless allow_download
 
     begin
       blob.open do |file|
         sha256 = Digest::SHA256.file(file.path).hexdigest
-        blob.metadata['sha256'] = sha256
+        assign_metadata_sha256!(blob, sha256)
-        blob.save! if blob.changed?
         sha256
       end
     rescue ActiveStorage::FileNotFoundError, ArgumentError => error

backend/app/services/material_sync_importer.rb

@@ -148,8 +148,7 @@ class MaterialSyncImporter
         io: tempfile,
         filename: @attributes[:filename],
         content_type: @attributes[:content_type])
-    blob.metadata['sha256'] = file_sha256 if file_sha256.present?
+    MaterialFileSha256.assign_metadata_sha256!(blob, file_sha256)
-    blob.save! if blob.changed?
     tempfile.rewind
     blob
   end
@@ -226,7 +225,7 @@ class MaterialSyncImporter
     if expected_sha256.present?
       return false unless material.file.attached?
 
-      return material.file.blob.metadata['sha256'] == expected_sha256
+      return MaterialFileSha256.metadata_sha256(material.file.blob) == expected_sha256
     end
 
     !material.file.attached?

backend/app/services/material_version_recorder.rb

@@ -57,7 +57,7 @@ class MaterialVersionRecorder < VersionRecorder
       file_content_type: blob.content_type,
       file_byte_size: blob.byte_size,
       file_checksum: blob.checksum,
-      file_sha256: blob.metadata['sha256'] }
+      file_sha256: MaterialFileSha256.metadata_sha256(blob) }
   end
 
   def empty_file_snapshot

backend/db/schema.rb

@@ -72,6 +72,7 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_26_010000) do
     t.index ["correct_post_id"], name: "index_gekanator_games_on_correct_post_id"
     t.index ["guessed_post_id"], name: "index_gekanator_games_on_guessed_post_id"
     t.index ["user_id"], name: "index_gekanator_games_on_user_id"
+    t.check_constraint "`question_count` >= 0", name: "chk_gekanator_games_question_count_nonnegative"
   end
 
   create_table "gekanator_question_examples", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
@@ -274,9 +275,10 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_26_010000) do
     t.datetime "created_at", null: false
     t.bigint "created_by_user_id"
     t.index ["created_at"], name: "index_nico_tag_versions_on_created_at"
-    t.index ["created_by_user_id", "created_at"], name: "index_nico_tag_versions_on_created_by_user_id_and_created_at"
+    t.index ["created_by_user_id", "created_at"], name: "index_nico_tag_versions_on_created_by_user_id_and_created_at", order: { created_at: :desc }
-    t.index ["tag_id", "created_at"], name: "index_nico_tag_versions_on_tag_id_and_created_at"
+    t.index ["tag_id", "created_at"], name: "index_nico_tag_versions_on_tag_id_and_created_at", order: { created_at: :desc }
     t.index ["tag_id", "version_no"], name: "index_nico_tag_versions_on_tag_id_and_version_no", unique: true
+    t.check_constraint "`version_no` > 0", name: "nico_tag_versions_version_no_positive"
   end
 
   create_table "post_implications", primary_key: ["post_id", "parent_post_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
@@ -285,13 +287,14 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_26_010000) do
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.index ["parent_post_id"], name: "index_post_implications_on_parent_post_id"
+    t.check_constraint "`post_id` <> `parent_post_id`", name: "chk_post_implications_no_self"
   end
 
   create_table "post_similarities", primary_key: ["post_id", "target_post_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "post_id", null: false
     t.bigint "target_post_id", null: false
     t.float "cos", null: false
-    t.index ["post_id", "cos"], name: "index_post_similarities_on_post_id_and_cos"
+    t.index ["post_id", "cos"], name: "index_post_similarities_on_post_id_and_cos", order: { cos: :desc }
     t.index ["target_post_id"], name: "index_post_similarities_on_target_post_id"
   end
 
@@ -331,6 +334,8 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_26_010000) do
     t.index ["created_by_user_id"], name: "index_post_versions_on_created_by_user_id"
     t.index ["post_id", "version_no"], name: "index_post_versions_on_post_id_and_version_no", unique: true
     t.index ["post_id"], name: "index_post_versions_on_post_id"
+    t.check_constraint "`event_type` in (_utf8mb4'create',_utf8mb4'update',_utf8mb4'discard',_utf8mb4'restore')", name: "post_versions_event_type_valid"
+    t.check_constraint "`version_no` > 0", name: "post_versions_version_no_positive"
   end
 
   create_table "posts", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
@@ -345,6 +350,7 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_26_010000) do
     t.integer "version_no", null: false
     t.index ["uploaded_user_id"], name: "index_posts_on_uploaded_user_id"
     t.index ["url"], name: "index_posts_on_url", unique: true
+    t.check_constraint "`version_no` > 0", name: "chk_posts_version_no_positive"
   end
 
   create_table "settings", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
@@ -391,7 +397,7 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_26_010000) do
     t.bigint "tag_id", null: false
     t.bigint "target_tag_id", null: false
     t.float "cos", null: false
-    t.index ["tag_id", "cos"], name: "index_tag_similarities_on_tag_id_and_cos"
+    t.index ["tag_id", "cos"], name: "index_tag_similarities_on_tag_id_and_cos", order: { cos: :desc }
     t.index ["target_tag_id"], name: "index_tag_similarities_on_target_tag_id"
   end
 
@@ -401,30 +407,32 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_26_010000) do
     t.string "event_type", null: false
     t.string "name", null: false
     t.string "category", null: false
+    t.datetime "deprecated_at"
     t.text "aliases", null: false
     t.text "parent_tag_ids", null: false
-    t.datetime "deprecated_at"
     t.datetime "created_at", null: false
     t.bigint "created_by_user_id"
     t.index ["created_at"], name: "index_tag_versions_on_created_at"
-    t.index ["created_by_user_id", "created_at"], name: "index_tag_versions_on_created_by_user_id_and_created_at"
+    t.index ["created_by_user_id", "created_at"], name: "index_tag_versions_on_created_by_user_id_and_created_at", order: { created_at: :desc }
-    t.index ["tag_id", "created_at"], name: "index_tag_versions_on_tag_id_and_created_at"
+    t.index ["tag_id", "created_at"], name: "index_tag_versions_on_tag_id_and_created_at", order: { created_at: :desc }
     t.index ["tag_id", "version_no"], name: "index_tag_versions_on_tag_id_and_version_no", unique: true
+    t.check_constraint "`version_no` > 0", name: "tag_versions_version_no_positive"
   end
 
   create_table "tags", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "tag_name_id", null: false
     t.string "category", default: "general", null: false
-    t.datetime "deprecated_at"
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.integer "post_count", default: 0, null: false
+    t.datetime "deprecated_at"
     t.datetime "discarded_at"
     t.integer "version_no", null: false
     t.index ["deprecated_at"], name: "index_tags_on_deprecated_at"
     t.index ["discarded_at"], name: "index_tags_on_discarded_at"
     t.index ["tag_name_id"], name: "index_tags_on_tag_name_id", unique: true
     t.check_constraint "(`deprecated_at` is null) or (`category` <> _utf8mb4'nico')", name: "chk_tags_deprecated_at_not_nico"
+    t.check_constraint "`version_no` > 0", name: "chk_tags_version_no_positive"
   end
 
   create_table "theatre_comments", primary_key: ["theatre_id", "no"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
@@ -549,6 +557,19 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_26_010000) do
     t.index ["banned_at"], name: "index_users_on_banned_at"
   end
 
+  create_table "wiki_assets", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "wiki_page_id", null: false
+    t.integer "no", null: false
+    t.string "alt_text"
+    t.binary "sha256", limit: 32, null: false
+    t.bigint "created_by_user_id", null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["created_by_user_id"], name: "index_wiki_assets_on_created_by_user_id"
+    t.index ["wiki_page_id", "no"], name: "index_wiki_assets_on_wiki_page_id_and_no", unique: true
+    t.index ["wiki_page_id", "sha256"], name: "index_wiki_assets_on_wiki_page_id_and_sha256", unique: true
+  end
+
   create_table "wiki_lines", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "sha256", limit: 64, null: false
     t.text "body", null: false
@@ -565,11 +586,13 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_26_010000) do
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.datetime "discarded_at"
+    t.integer "next_asset_no", default: 1, null: false
     t.integer "version_no", null: false
     t.index ["created_user_id"], name: "index_wiki_pages_on_created_user_id"
     t.index ["discarded_at"], name: "index_wiki_pages_on_discarded_at"
     t.index ["tag_name_id"], name: "index_wiki_pages_on_tag_name_id", unique: true
     t.index ["updated_user_id"], name: "index_wiki_pages_on_updated_user_id"
+    t.check_constraint "`version_no` > 0", name: "chk_wiki_pages_version_no_positive"
   end
 
   create_table "wiki_revision_lines", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
@@ -614,6 +637,8 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_26_010000) do
     t.index ["created_by_user_id"], name: "index_wiki_versions_on_created_by_user_id"
     t.index ["wiki_page_id", "version_no"], name: "index_wiki_versions_on_wiki_page_id_and_version_no", unique: true
     t.index ["wiki_page_id"], name: "index_wiki_versions_on_wiki_page_id"
+    t.check_constraint "`event_type` in (_utf8mb4'create',_utf8mb4'update',_utf8mb4'discard',_utf8mb4'restore')", name: "wiki_versions_event_type_valid"
+    t.check_constraint "`version_no` > 0", name: "wiki_versions_version_no_positive"
   end
 
   add_foreign_key "active_storage_attachments", "active_storage_blobs", column: "blob_id"
@@ -692,6 +717,8 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_26_010000) do
   add_foreign_key "user_ips", "users"
   add_foreign_key "user_post_views", "posts"
   add_foreign_key "user_post_views", "users"
+  add_foreign_key "wiki_assets", "users", column: "created_by_user_id"
+  add_foreign_key "wiki_assets", "wiki_pages"
   add_foreign_key "wiki_pages", "tag_names"
   add_foreign_key "wiki_pages", "users", column: "created_user_id"
   add_foreign_key "wiki_pages", "users", column: "updated_user_id"

backend/spec/models/material_spec.rb

@@ -0,0 +1,19 @@
+require 'rails_helper'
+
+RSpec.describe Material, type: :model do
+  let(:user) { create(:user, :member) }
+
+  it 'allows only material source kinds, not suppression prefix kinds' do
+    material = described_class.new(url: 'https://example.com/material',
+                                   source_kind: 'google_drive_path_prefix',
+                                   source_path: '素材/危険',
+                                   created_by_user: user,
+                                   updated_by_user: user)
+
+    expect(material).not_to be_valid
+    expect(material.errors[:source_kind]).to be_present
+
+    material.source_kind = 'google_drive_path'
+    expect(material).to be_valid
+  end
+end

backend/spec/requests/materials_spec.rb

@@ -113,6 +113,68 @@ RSpec.describe 'Materials API', type: :request do
       expect(response_materials.size).to eq(1)
       expect(response_materials.first['id']).to eq(material_b.id)
     end
+
+    it 'filters by descendant tags and returns stable parent tag groups' do
+      root =
+          Tag.create!(tag_name: TagName.create!(name: 'material_scope_root'),
+                      category: :material)
+      child_b =
+          Tag.create!(tag_name: TagName.create!(name: 'material_scope_b'),
+                      category: :material)
+      child_a =
+          Tag.create!(tag_name: TagName.create!(name: 'material_scope_a'),
+                      category: :material)
+      deprecated =
+          Tag.create!(tag_name: TagName.create!(name: 'material_scope_old'),
+                      category: :material,
+                      deprecated_at: Time.current)
+      grandchild =
+          Tag.create!(tag_name: TagName.create!(name: 'material_scope_grandchild'),
+                      category: :material)
+      root_material =
+          build_material(tag: root, user: member_user,
+                         file: dummy_upload(filename: 'root.png'))
+      child_a_material =
+          build_material(tag: child_a, user: member_user,
+                         file: dummy_upload(filename: 'child_a.png'))
+      grandchild_material =
+          build_material(tag: grandchild, user: member_user,
+                         file: dummy_upload(filename: 'grandchild.png'))
+
+      TagImplication.create!(parent_tag: root, tag: child_b)
+      TagImplication.create!(parent_tag: root, tag: child_a)
+      TagImplication.create!(parent_tag: child_b, tag: deprecated)
+      TagImplication.create!(parent_tag: deprecated, tag: grandchild)
+
+      get '/materials',
+          params: { tag_id: root.id, include_descendants: '1',
+                    group_by: 'parent_tag', sort: 'id', direction: 'asc' }
+
+      expect(response).to have_http_status(:ok)
+      expect(response_materials.map { |m| m['id'] })
+        .to include(root_material.id, child_a_material.id, grandchild_material.id)
+      expect(json['tag_scope']).to eq(
+        'tag' => {
+          'id' => root.id,
+          'name' => 'material_scope_root',
+          'category' => 'material'
+        },
+        'include_descendants' => true
+      )
+      expect(json['groups'].map { |group| group.dig('tag', 'name') })
+        .to eq(['material_scope_a', 'material_scope_b', 'material_scope_root'])
+      expect(json['groups'].find { |group| group.dig('tag', 'id') == child_b.id }
+        .fetch('material_ids')).to eq([grandchild_material.id])
+    end
+
+    it 'returns nil tag_scope when tag_id is unknown' do
+      get '/materials', params: { tag_id: 999_999, group_by: 'parent_tag' }
+
+      expect(response).to have_http_status(:ok)
+      expect(json['tag_scope']).to be_nil
+      expect(json['groups']).to eq([])
+      expect(response_materials).to eq([])
+    end
   end
 
   describe 'GET /materials/:id' do

backend/spec/services/material_file_sha256_spec.rb

@@ -0,0 +1,23 @@
+require 'rails_helper'
+
+RSpec.describe MaterialFileSha256 do
+  describe '.metadata_sha256' do
+    it 'reads sha256 from Hash metadata' do
+      blob = instance_double(ActiveStorage::Blob, metadata: { 'sha256' => 'abc123' })
+
+      expect(described_class.metadata_sha256(blob)).to eq('abc123')
+    end
+
+    it 'reads sha256 from JSON string metadata' do
+      blob = instance_double(ActiveStorage::Blob, metadata: '{"sha256":"abc123"}')
+
+      expect(described_class.metadata_sha256(blob)).to eq('abc123')
+    end
+
+    it 'returns nil for invalid metadata' do
+      blob = instance_double(ActiveStorage::Blob, metadata: '{')
+
+      expect(described_class.metadata_sha256(blob)).to be_nil
+    end
+  end
+end

frontend/src/pages/materials/MaterialListPage.test.tsx

@@ -126,4 +126,70 @@ describe ('MaterialListPage', () => {
     expect (screen.getByText ('サイズ:')).toBeInTheDocument ()
     expect (screen.getByText ('2.0 KB')).toBeInTheDocument ()
   })
+
+  it ('shows the selected tag scope and tag-specific add links', async () => {
+    api.apiGet.mockResolvedValueOnce ({
+      materials: [
+        buildMaterial ({
+          id:  10,
+          tag: buildTag ({ id: 30, name: '泣き', category: 'material' }),
+        }),
+      ],
+      count:    1,
+      tagScope: {
+        tag:                { id: 20, name: '伊地知ニジカ', category: 'material' },
+        includeDescendants: true,
+      },
+      groups: [
+        {
+          key:         'tag:30',
+          tag:         { id: 30, name: '泣き', category: 'material' },
+          materialIds: [10],
+          count:       1,
+        },
+      ],
+    })
+
+    renderWithProviders (
+        <MaterialListPage/>,
+        { route: '/materials?tag_id=20&include_descendants=1&group_by=parent_tag' },
+    )
+
+    expect (await screen.findByText (
+        (_, element) => element?.textContent === '伊地知ニジカ 配下の素材を表示中',
+    )).toBeInTheDocument ()
+
+    const addLinks = screen.getAllByRole ('link', { name: 'このタグに素材を追加' })
+    expect (addLinks[0]).toHaveAttribute (
+        'href',
+        '/materials/new?tag=%E4%BC%8A%E5%9C%B0%E7%9F%A5%E3%83%8B%E3%82%B8%E3%82%AB'
+        + '&return_to=%2Fmaterials%3Ftag_id%3D20%26include_descendants%3D1%26group_by%3Dparent_tag',
+    )
+    expect (addLinks[1]).toHaveAttribute (
+        'href',
+        '/materials/new?tag=%E6%B3%A3%E3%81%8D'
+        + '&return_to=%2Fmaterials%3Ftag_id%3D20%26include_descendants%3D1%26group_by%3Dparent_tag',
+    )
+    expect (screen.getByRole ('link', { name: 'タグ選択を解除' })).toHaveAttribute (
+        'href',
+        '/materials?material_filter=present',
+    )
+  })
+
+  it ('shows a clear link when tag_id does not resolve to tag_scope', async () => {
+    api.apiGet.mockResolvedValueOnce ({
+      materials: [],
+      count:     0,
+      tagScope:  null,
+      groups:    [],
+    })
+
+    renderWithProviders (<MaterialListPage/>, { route: '/materials?tag_id=999' })
+
+    expect (await screen.findByText ('選択中タグが見つかりません．')).toBeInTheDocument ()
+    expect (screen.getByRole ('link', { name: 'タグ選択を解除' })).toHaveAttribute (
+        'href',
+        '/materials?material_filter=present',
+    )
+  })
 })

frontend/src/pages/materials/MaterialListPage.tsx

@@ -106,7 +106,7 @@ const clearedTagSelectionPath = (
     const qs = new URLSearchParams (locationSearch)
     qs.delete ('tag_id')
     qs.delete ('include_descendants')
-    qs.set ('group_by', 'none')
+    qs.delete ('group_by')
     qs.delete ('page')
     qs.set ('material_filter', materialFilter)
     return `/materials?${ qs.toString () }`
@@ -471,6 +471,18 @@ const MaterialListPage: FC = () => {
 		  タグ選択を解除
 		</PrefetchLink>
 	      </div>)}
+	  {(tagId != null && tagScope == null) && (
+	      <div className="flex flex-wrap items-center gap-3 rounded-lg border
+			      border-amber-200 bg-amber-50 px-4 py-3 text-sm text-amber-900
+			      dark:border-amber-800 dark:bg-amber-950 dark:text-amber-100">
+		<span>選択中タグが見つかりません．</span>
+		<PrefetchLink
+		    to={clearedTagSelectionPath (location.search, materialFilter)}
+		    className="font-medium underline underline-offset-2
+			       text-amber-800 dark:text-amber-200">
+		  タグ選択を解除
+		</PrefetchLink>
+	      </div>)}
 
 	  {tagState === 'untagged' && (
 	      <PrefetchLink

frontend/src/pages/materials/MaterialNewPage.test.tsx

@@ -1,5 +1,6 @@
 import { fireEvent, screen, waitFor } from '@testing-library/react'
 import { beforeEach, describe, expect, it, vi } from 'vitest'
+import { Route, Routes, useLocation } from 'react-router-dom'
 
 import MaterialNewPage from '@/pages/materials/MaterialNewPage'
 import { renderWithProviders } from '@/test/render'
@@ -17,6 +18,11 @@ const toastApi = vi.hoisted (() => ({
 vi.mock ('@/lib/api', () => api)
 vi.mock ('@/components/ui/use-toast', () => toastApi)
 
+const LocationView = () => {
+  const location = useLocation ()
+  return <div>{location.pathname + location.search}</div>
+}
+
 describe ('MaterialNewPage', () => {
   beforeEach (() => {
     vi.clearAllMocks ()
@@ -69,4 +75,50 @@ describe ('MaterialNewPage', () => {
     expect (await screen.findAllByText ('ファイルまたは URL は必須です．')).toHaveLength (2)
     expect (screen.getAllByRole ('textbox')[1]).toHaveAttribute ('aria-invalid', 'true')
   })
+
+  it ('returns only to safe material URLs after successful creation', async () => {
+    api.apiPost.mockResolvedValueOnce ({})
+
+    renderWithProviders (
+        <Routes>
+          <Route path="/materials/new" element={<MaterialNewPage/>}/>
+          <Route path="/materials" element={<LocationView/>}/>
+        </Routes>,
+        {
+          route:
+              '/materials/new?tag=%E8%99%B9%E5%A4%8F'
+              + '&return_to=%2Fmaterials%3Ftag_id%3D20',
+        },
+    )
+
+    fireEvent.change (screen.getAllByRole ('textbox')[1], {
+      target: { value: 'https://example.com/ref' },
+    })
+    fireEvent.click (screen.getByRole ('button', { name: '追加' }))
+
+    expect (await screen.findByText ('/materials?tag_id=20')).toBeInTheDocument ()
+  })
+
+  it ('ignores unsafe return_to values after successful creation', async () => {
+    api.apiPost.mockResolvedValueOnce ({})
+
+    renderWithProviders (
+        <Routes>
+          <Route path="/materials/new" element={<MaterialNewPage/>}/>
+          <Route path="/materials" element={<LocationView/>}/>
+        </Routes>,
+        {
+          route:
+              '/materials/new?tag=%E8%99%B9%E5%A4%8F'
+              + '&return_to=https%3A%2F%2Fexample.com%2Fevil',
+        },
+    )
+
+    fireEvent.change (screen.getAllByRole ('textbox')[1], {
+      target: { value: 'https://example.com/ref' },
+    })
+    fireEvent.click (screen.getByRole ('button', { name: '追加' }))
+
+    expect (await screen.findByText ('/materials')).toBeInTheDocument ()
+  })
 })

frontend/src/pages/materials/MaterialNewPage.tsx

@@ -28,6 +28,7 @@ const MaterialNewPage: FC = () => {
   const query = new URLSearchParams (location.search)
   const tagQuery = query.get ('tag') ?? ''
   const returnToQuery = query.get ('return_to') ?? ''
+  const safeReturnTo = returnToQuery.startsWith ('/materials') ? returnToQuery : ''
 
   const navigate = useNavigate ()
 
@@ -55,7 +56,7 @@ const MaterialNewPage: FC = () => {
       onSuccess: async () => {
 	await qc.invalidateQueries ({ queryKey: materialsKeys.root })
 	toast ({ title: '送信成功!' })
-	navigate (returnToQuery || `/materials?tag=${ encodeURIComponent (tag) }`)
+	navigate (safeReturnTo || '/materials')
       },
       onError: error => {
 	applyValidationError (error)