fix(canvas): [PKG-CANVAS-04] preserve public type and export compatibility

test/types/canvas.ts

@@ -0,0 +1,59 @@
+import type { Factory, MediaCanvas, Option, Result } from 'artplayer-proxy-canvas'
+import Artplayer from 'artplayer'
+import canvas from 'artplayer-proxy-canvas'
+import legacy from 'artplayer-proxy-canvas/legacy'
+
+type Equal<A, B> = (<T>() => T extends A ? 1 : 2) extends (<T>() => T extends B ? 1 : 2) ? true : false
+type Assert<T extends true> = T
+type OptionalInput = Assert<Equal<Parameters<typeof canvas>, [option?: Option]>>
+type ExactResult = Assert<Equal<ReturnType<ReturnType<typeof canvas>>, HTMLCanvasElement>>
+
+const option: Option = (context, video) => {
+  context.drawImage(video, 0, 0)
+  const source: HTMLVideoElement = video
+  const ctx: CanvasRenderingContext2D = context
+  void [source, ctx]
+}
+const art = new Artplayer({ container: '#player', url: 'video.mp4', proxy: canvas(option) })
+canvas()
+canvas(undefined)
+canvas.default(option)
+legacy.default()
+declare const optional: Option | undefined
+canvas(optional)
+const missing: Parameters<typeof canvas>[0] = undefined
+const factory: Factory = canvas
+const registration: (art: Artplayer) => HTMLCanvasElement = factory()
+const result: Result = registration(art)
+const originalResult: Result = document.createElement('canvas')
+const media = result as MediaCanvas
+const play: Promise<void> = media.play()
+media.pause()
+media.src = 'replacement.mp4'
+const context: CanvasRenderingContext2D | null = media.getContext('2d')
+const listen: HTMLCanvasElement['addEventListener'] = media.addEventListener
+const width: number = media.width
+// @ts-expect-error Callback remains a function.
+canvas(42)
+// @ts-expect-error Strings are not typed callbacks.
+canvas('callback')
+// @ts-expect-error Historical runtime tolerates null, but published types never accepted it.
+canvas(null)
+// @ts-expect-error The callback receives a 2D context.
+canvas((ctx: WebGLRenderingContext) => void ctx)
+// @ts-expect-error The callback receives video, not canvas.
+canvas((ctx: CanvasRenderingContext2D, video: HTMLCanvasElement) => void [ctx, video])
+// @ts-expect-error Canvas return must not be relabeled as a native video.
+const video: HTMLVideoElement = result
+// @ts-expect-error Registration remains synchronous.
+const promise: Promise<HTMLCanvasElement> = canvas()(art)
+// @ts-expect-error 2D contexts have no media play method.
+media.getContext('2d')?.play()
+// @ts-expect-error Native Canvas dimensions remain numeric.
+media.width = '320'
+// @ts-expect-error Self default identity is readonly in declarations.
+canvas.default = legacy
+// @ts-expect-error Registration requires a host.
+canvas()()
+void [missing, originalResult, play, context, listen, width, video, promise]
+export type { ExactResult, OptionalInput }