The declaration describes the existing tool class, not an ArtPlayer plugin factory. The previous workspace manifest pointed to a missing declaration. There is no recovered legacy declaration to claim as an exact TypeScript baseline.

Entry	Declaration	Runtime
Root ESM import	artplayer-tool-thumbnail.d.mts	Default constructor in dist/artplayer-tool-thumbnail.mjs
Root require	artplayer-tool-thumbnail.d.cts	Direct constructor in dist/artplayer-tool-thumbnail.js
Older Node resolution / TS 4.3	artplayer-tool-thumbnail.d.ts	main points to the direct CommonJS constructor
artplayer-tool-thumbnail/legacy	d.cts or typesVersions fallback	Direct legacy constructor; native ESM gets its default
Browser script / editor	Generated docs/assets/ts declaration	ArtplayerToolThumbnail global

The d.ts file is the public source of truth. d.cts forwards its export assignment; d.mts exposes the default constructor and type-only named exports. No runtime named exports or .default self-alias exist. Keep the wrappers sharing one class.

import Thumbnail, { Option } from 'artplayer-tool-thumbnail'

const input = document.createElement('input')
input.type = 'file'
const options: Option = { fileInput: input, number: 10 }
const tool = new Thumbnail(options)
tool.on('update', (url, progress) => console.log(url, progress))
tool.on('custom', (value: number) => console.log(value))
tool.emit('custom', 1)

CommonJS TS can use import Thumbnail = require('artplayer-tool-thumbnail') without esModuleInterop. The optional constructor argument mirrors the JS signature, but successful initialization requires fileInput to be an actual file input or Element wrapper. Missing input throws synchronously. setup accepts partial options and retains unknown fields. Numeric range/clamp validation remains a runtime condition.

Known event tuples are precise. Custom string/number/symbol events infer annotated callback arguments; those protocols remain the caller's responsibility. ctx is inferred from the optional third argument. Dispatch through emit to retain event argument checks rather than directly invoking the heterogeneous e registry. file/videoUrl/thumbnailUrl/density may be absent before their operation. start returns Promise; ready-metadata preflight may throw synchronously, and source replacement/destroy reject with AbortError. Error events usually contain strings, but callback throws can supply any message value, so narrow unknown first.

Source/declaration constructors are mutually checked in test/types/thumbnail-source.ts. Current and TS 4.3.5 consumers include ten invalid uses. Installed checks pack/install outside the workspace, offline with an unchanged frozen lock, verify every file and exercise native Node require/import without a DOM.

yarn test:thumbnail
yarn test:thumbnail-types-package
yarn build:ts
yarn test:browser test/browser/thumbnail-editor-types.spec.js

build:ts selects package declaration entries rather than auxiliary types and emits the uppercase global. Actual file extraction, old-core composition and the full demo remain separate checks. The 3.5.31 versus 4.4.0 default policy remains pending.