diff --git a/src/interface/keyframeEasingsPopup.ts b/src/interface/keyframeEasingsPopup.ts
index 5d155b6b..07ade3d3 100644
--- a/src/interface/keyframeEasingsPopup.ts
+++ b/src/interface/keyframeEasingsPopup.ts
@@ -2,52 +2,44 @@
 // - 選択中 keyframe (= .keyframe.selected) を mouseover した時に keyframe element の右側に popup mount
 // - popup 内は keyframeEasingsPopup.svelte (= 既存 easing UI + XYZ input)
 // - mouse が keyframe / popup の両方から離れた時に unmount (= 100ms grace で chatter 防止)
-// - blockbench-anim-ux (= 別 plugin) が居る場合は popout 子窓内でも動作する (= window.AnimUX 経由)
+// - blockbench-anim-ux (= 別 plugin) が居る場合は popout 子窓内でも動作する
 
 import { registerPatch } from 'blockbench-patch-manager'
 import { injectComponent } from 'svelte-patching-tools'
 import { activeProjectIsBlueprintFormat } from '../formats/blueprint'
 import KeyframeEasingsPopupSvelte from '../svelteComponents/keyframeEasingsPopup.svelte'
 import { isFirstKeyframe } from '../panels/easings/easings.svelte'
+import { subscribeAnimUxDocuments } from '../util/animUxTimeline'
 
-// blockbench-anim-ux (= sibling plugin) が公開する optional API。
-// 居ない場合は素の document.addEventListener にフォールバックする。
-type AnimUxExternal = {
-	version: string
-	addDocumentListener(
-		type: string,
-		fn: EventListenerOrEventListenerObject,
-		opts?: boolean | AddEventListenerOptions,
-	): () => void
-	getActivePopoutDocument(): Document | null
-}
-
-function getAnimUx(): AnimUxExternal | undefined {
-	return (window as unknown as { AnimUX?: AnimUxExternal }).AnimUX
-}
-
-// 親 document に直登録 + 必要なら popout 子窓にも attach する helper。
-// anim_ux 未 install / 旧 version (= addDocumentListener 未対応) でも害なく degrade する。
 function attachDocListener(
 	type: string,
 	fn: EventListenerOrEventListenerObject,
 	opts?: boolean | AddEventListenerOptions,
 ): () => void {
-	const animUx = getAnimUx()
-	if (animUx?.addDocumentListener) {
-		try {
-			return animUx.addDocumentListener(type, fn, opts)
-		} catch (e) {
-			console.warn('[AJ] AnimUX.addDocumentListener failed, fallback to document', e)
+	let attachedDocuments: Document[] = []
+
+	const detach = (): void => {
+		for (const ownerDocument of attachedDocuments) {
+			ownerDocument.removeEventListener(
+				type,
+				fn,
+				opts as boolean | EventListenerOptions | undefined,
+			)
 		}
+		attachedDocuments = []
 	}
-	document.addEventListener(type, fn, opts)
-	return (): void => {
-		try {
-			document.removeEventListener(type, fn, opts as boolean | EventListenerOptions | undefined)
-		} catch {
-			/* noop */
+
+	const unsubscribeDocuments = subscribeAnimUxDocuments(documents => {
+		detach()
+		attachedDocuments = [...new Set(documents)]
+		for (const ownerDocument of attachedDocuments) {
+			ownerDocument.addEventListener(type, fn, opts)
 		}
+	})
+
+	return (): void => {
+		unsubscribeDocuments()
+		detach()
 	}
 }
 
@@ -354,8 +346,8 @@ function applyToActiveInput(active: HTMLInputElement, delta: number): void {
 	// popup が popout 子窓に乗っている場合は parent realm の Event を投げると realm 不一致を踏むので、
 	// active 自身の owner realm の Event constructor を使う。
 	const ownerWin = active.ownerDocument?.defaultView
-	const EventCtor = (ownerWin?.Event as typeof Event | undefined) ?? Event
-	active.dispatchEvent(new EventCtor('input', { bubbles: true }))
+	const eventCtor = (ownerWin?.Event as typeof Event | undefined) ?? Event
+	active.dispatchEvent(new eventCtor('input', { bubbles: true }))
 }
 
 // event の発生元 document を割り出す helper。
@@ -371,7 +363,7 @@ function onAxisKeyCapture(e: KeyboardEvent): void {
 	// plain も含めて全部 capture で処理 (= type=text にしたので browser 標準 Arrow は無関係、
 	// 全 case で自前 getInterval が必要)
 	const active = getEventDocument(e).activeElement as HTMLInputElement | null
-	if (!active || !active.matches(`#${POPUP_ID} input[data-axis]`)) return
+	if (!active?.matches(`#${POPUP_ID} input[data-axis]`)) return
 
 	e.preventDefault()
 	e.stopPropagation()
@@ -383,7 +375,7 @@ function onAxisKeyCapture(e: KeyboardEvent): void {
 
 function onAxisWheelCapture(e: WheelEvent): void {
 	const active = getEventDocument(e).activeElement as HTMLInputElement | null
-	if (!active || !active.matches(`#${POPUP_ID} input[data-axis]`)) return
+	if (!active?.matches(`#${POPUP_ID} input[data-axis]`)) return
 	if (e.target !== active) return
 
 	e.preventDefault()
@@ -399,8 +391,7 @@ registerPatch({
 
 	apply: () => {
 		const cssDeletable = Blockbench.addCSS(POPUP_CSS)
-		// anim_ux 経由で attach すると popout 中の子窓 document にも自動で追従する。
-		// 未 install / 旧 version では document.addEventListener にフォールバック (= attachDocListener 内処理)。
+		// anim_ux の document stream に attach し、未 install 時は親 document へフォールバックする。
 		const detachOnMouseOver = attachDocListener('mouseover', onMouseOver, true)
 		const detachOnMouseOut = attachDocListener('mouseout', onMouseOut, true)
 		const detachOnAxisKey = attachDocListener('keydown', onAxisKeyCapture, true)
diff --git a/src/mods/keyframeEasingVisualMod.ts b/src/mods/keyframeEasingVisualMod.ts
index b82988c4..92824fb5 100644
--- a/src/mods/keyframeEasingVisualMod.ts
+++ b/src/mods/keyframeEasingVisualMod.ts
@@ -7,6 +7,7 @@
 import { registerPatch } from 'blockbench-patch-manager'
 import { activeProjectIsBlueprintFormat } from '../formats/blueprint'
 import EVENTS from '../util/events'
+import { subscribeAnimUxDocuments } from '../util/animUxTimeline'
 
 type EasingDir = 'in' | 'out' | 'inout'
 
@@ -80,17 +81,12 @@ function parseEasing(easing: string | undefined): { type: string; dir: EasingDir
 	return { type: m[2].toLowerCase(), dir: m[1].toLowerCase() as EasingDir }
 }
 
-// anim_ux v0.6+ が公開する popout 子窓 document。 popout 中は keyframe DOM が子窓側に
-// adoptNode 移植されるため、 親 document の querySelector では見つからない。 attach 中の
-// すべての document を順に探して最初に当たった要素に attribute を当てる。
-let popoutDoc: Document | null = null
-
-function getActiveDocs(): Document[] {
-	return popoutDoc ? [document, popoutDoc] : [document]
-}
+// popout 中は keyframe DOM が子窓側へ adoptNode 移植されるため、親 document の
+// querySelector では見つからない。現在の document stream を順に探して要素へ attribute を当てる。
+let activeDocuments: readonly Document[] = []
 
 function findKeyframeElement(uuid: string): HTMLElement | null {
-	for (const doc of getActiveDocs()) {
+	for (const doc of activeDocuments) {
 		const el = doc.querySelector<HTMLElement>(`.keyframe[id="${uuid}"]`)
 		if (el) return el
 	}
@@ -136,79 +132,67 @@ function findKeyframeByUuid(uuid: string): _Keyframe | undefined {
 	return undefined
 }
 
-// MutationObserver の addedNodes に直接 .keyframe が来るとは限らず、 BB が channel 親要素ごと
-// 再描画した場合は親 element が addedNodes に入る (= reviewer 指摘 B3)。 加えて easing 変更時は
-// UPDATE_KEYFRAME_SELECTION が発火しないため event 経路では visual 更新されない (= reviewer 指摘 B6)。
+// MutationObserver の addedNodes に直接 .keyframe が来るとは限らず、BB が channel 親要素ごと
+// 再描画した場合は親 element が addedNodes に入る。加えて easing 変更時は
+// UPDATE_KEYFRAME_SELECTION が発火しないため、event 経路では visual 更新されない。
 // addedNode 自身 + 子孫の .keyframe を再帰探索して個別 applyDataset で attribute 再付与する。
 function syncSubtreeKeyframes(root: Node): void {
-	if (!(root instanceof HTMLElement)) return
-	if (root.classList?.contains('keyframe') && root.id) {
-		const kf = findKeyframeByUuid(root.id)
+	if (root.nodeType !== 1) return
+	const element = root as Element
+	if (element.classList.contains('keyframe') && element.id) {
+		const kf = findKeyframeByUuid(element.id)
 		if (kf) applyDataset(kf)
 	}
-	root.querySelectorAll?.<HTMLElement>('.keyframe').forEach(child => {
+	element.querySelectorAll<HTMLElement>('.keyframe').forEach(child => {
 		if (!child.id) return
 		const kf = findKeyframeByUuid(child.id)
 		if (kf) applyDataset(kf)
 	})
 }
 
-// popout 子窓 document への CSS + MutationObserver attach 状態。 同時に複数子窓を想定しない
-// (= anim_ux は同時 1 子窓のみ) ため単一 slot で管理。
-interface PopoutAttach {
+interface DocumentAttach {
 	doc: Document
-	baseStyle: HTMLStyleElement
-	curveStyle: HTMLStyleElement
+	baseStyle?: HTMLStyleElement
+	curveStyle?: HTMLStyleElement
 	observer: MutationObserver
 }
-let popoutAttach: PopoutAttach | null = null
 
-function attachPopoutDoc(doc: Document): void {
-	if (popoutAttach?.doc === doc) return
-	if (popoutAttach) detachPopoutDoc()
-	// CSS は親 head 経由 (Blockbench.addCSS) では popout 子窓に伝播しないので、
-	// 子窓 head に直接 <style> を inject する。 親側は別途 Blockbench.addCSS で済んでいる。
-	const baseStyle = doc.createElement('style')
-	baseStyle.textContent = BASE_CSS
-	doc.head.appendChild(baseStyle)
-	const curveStyle = doc.createElement('style')
-	curveStyle.textContent = buildCurveCss()
-	doc.head.appendChild(curveStyle)
-	const observer = new MutationObserver(mutations => {
-		for (const m of mutations) {
-			for (const node of m.addedNodes) syncSubtreeKeyframes(node)
-		}
-	})
-	observer.observe(doc.body, { childList: true, subtree: true })
-	popoutAttach = { doc, baseStyle, curveStyle, observer }
-	popoutDoc = doc
-	// popout 開いた瞬間に既に居る keyframe (= adoptNode 直後の DOM) を即時 sync
-	refreshAllKeyframes()
-}
+let documentAttaches: DocumentAttach[] = []
 
-function detachPopoutDoc(): void {
-	if (!popoutAttach) return
-	popoutAttach.observer.disconnect()
-	try {
-		popoutAttach.baseStyle.remove()
-	} catch {
-		/* noop */
+function detachDocuments(): void {
+	for (const attachment of documentAttaches) {
+		attachment.observer.disconnect()
+		attachment.baseStyle?.remove()
+		attachment.curveStyle?.remove()
 	}
-	try {
-		popoutAttach.curveStyle.remove()
-	} catch {
-		/* noop */
+	documentAttaches = []
+	activeDocuments = []
+}
+
+function attachDocuments(documents: readonly Document[]): void {
+	detachDocuments()
+	for (const doc of new Set(documents)) {
+		if (!doc.body || !doc.head) continue
+		let baseStyle: HTMLStyleElement | undefined
+		let curveStyle: HTMLStyleElement | undefined
+		if (doc !== document) {
+			baseStyle = doc.createElement('style')
+			baseStyle.textContent = BASE_CSS
+			doc.head.appendChild(baseStyle)
+			curveStyle = doc.createElement('style')
+			curveStyle.textContent = buildCurveCss()
+			doc.head.appendChild(curveStyle)
+		}
+		const observer = new MutationObserver(mutations => {
+			for (const mutation of mutations) {
+				for (const node of mutation.addedNodes) syncSubtreeKeyframes(node)
+			}
+		})
+		observer.observe(doc.body, { childList: true, subtree: true })
+		documentAttaches.push({ doc, baseStyle, curveStyle, observer })
 	}
-	popoutAttach = null
-	popoutDoc = null
-}
-
-interface AnimUxAPI {
-	getActivePopoutDocument(): Document | null
-}
-
-interface PopoutEventDetail {
-	document: Document
+	activeDocuments = documentAttaches.map(attachment => attachment.doc)
+	refreshAllKeyframes()
 }
 
 registerPatch({
@@ -224,46 +208,14 @@ registerPatch({
 		)
 		const unsubProjectSelect = EVENTS.SELECT_AJ_PROJECT.subscribe(refreshAllKeyframes)
 
-		// BB が keyframe DOM を再描画する経路 (= 親 channel 再描画 / easing 変更 / animation 切替) で
-		// AJ 付与 attribute が消失する問題への補修。 addedNodes 内の .keyframe を子孫含めて再付与する。
-		// document.body 全体 subtree を監視するが、 .keyframe フィルタで処理を限定する。
-		const observer = new MutationObserver(mutations => {
-			for (const m of mutations) {
-				for (const node of m.addedNodes) syncSubtreeKeyframes(node)
-			}
-		})
-		observer.observe(document.body, { childList: true, subtree: true })
-
-		// anim_ux v0.6+ の popout event を listen。 popout 子窓には CSS / MutationObserver / dataset
-		// を別途 attach しないと easing の色変更と背景カーブが反映されない (= 親 document 経路は伝播しない)。
-		const onPopoutOpen = (e: Event): void => {
-			const detail = (e as CustomEvent<PopoutEventDetail>).detail
-			if (detail?.document) attachPopoutDoc(detail.document)
-		}
-		const onPopoutClose = (): void => {
-			detachPopoutDoc()
-			// popout 閉じた直後、 keyframe DOM が親 document に戻った後の再 sync
-			refreshAllKeyframes()
-		}
-		window.addEventListener('animux:popout-open', onPopoutOpen)
-		window.addEventListener('animux:popout-close', onPopoutClose)
-
-		// plugin 順序依存の安全弁 = AJ load 時点で既に popout 中の場合は event 来ない、
-		// anim_ux API 経由で現在状態を直接拾う。
-		const animux = (window as unknown as { AnimUX?: AnimUxAPI }).AnimUX
-		const existing = animux?.getActivePopoutDocument?.()
-		if (existing) attachPopoutDoc(existing)
-
-		refreshAllKeyframes()
+		const unsubscribeAnimUxDocuments = subscribeAnimUxDocuments(attachDocuments)
 
 		return {
 			baseCssDeletable,
 			curveCssDeletable,
 			unsubKeyframeSelection,
 			unsubProjectSelect,
-			observer,
-			onPopoutOpen,
-			onPopoutClose,
+			unsubscribeAnimUxDocuments,
 		}
 	},
 
@@ -272,25 +224,22 @@ registerPatch({
 		curveCssDeletable,
 		unsubKeyframeSelection,
 		unsubProjectSelect,
-		observer,
-		onPopoutOpen,
-		onPopoutClose,
+		unsubscribeAnimUxDocuments,
 	}) => {
-		window.removeEventListener('animux:popout-open', onPopoutOpen)
-		window.removeEventListener('animux:popout-close', onPopoutClose)
-		detachPopoutDoc()
-		observer.disconnect()
+		const documents = activeDocuments
+		unsubscribeAnimUxDocuments()
+		detachDocuments()
 		unsubKeyframeSelection()
 		unsubProjectSelect()
 		baseCssDeletable.delete()
 		curveCssDeletable.delete()
-		document
-			.querySelectorAll<HTMLElement>(
-				'.keyframe[data-aj-ease-type], .keyframe[data-aj-ease-dir]'
-			)
-			.forEach(el => {
+		for (const doc of documents) {
+			doc.querySelectorAll<HTMLElement>('.keyframe[data-aj-ease-type], .keyframe[data-aj-ease-dir]').forEach(
+			el => {
 				delete el.dataset.ajEaseType
 				delete el.dataset.ajEaseDir
-			})
+			}
+		)
+		}
 	},
 })
diff --git a/src/tests/animUxTimeline.test.ts b/src/tests/animUxTimeline.test.ts
new file mode 100644
index 00000000..dc7c0c4b
--- /dev/null
+++ b/src/tests/animUxTimeline.test.ts
@@ -0,0 +1,81 @@
+import { afterEach, describe, expect, it, vi } from 'vitest'
+import { ANIM_UX_READY_EVENT, subscribeAnimUxDocuments } from '../util/animUxTimeline'
+
+type ReadyListener = (data: unknown) => void
+
+interface FakeBlockbench {
+	on(eventName: string, listener: ReadyListener): void
+	removeListener(eventName: string, listener: ReadyListener): void
+	emit(eventName: string, data: unknown): void
+}
+
+function createBlockbench(): FakeBlockbench {
+	const listeners = new Map<string, ReadyListener>()
+	return {
+		on(eventName, listener) {
+			listeners.set(eventName, listener)
+		},
+		removeListener(eventName, listener) {
+			if (listeners.get(eventName) === listener) listeners.delete(eventName)
+		},
+		emit(eventName, data) {
+			listeners.get(eventName)?.(data)
+		},
+	}
+}
+
+afterEach(() => {
+	vi.unstubAllGlobals()
+})
+
+describe('subscribeAnimUxDocuments', () => {
+	it('uses the parent document until anim-ux becomes ready', () => {
+		const parentDocument = {} as Document
+		const blockbench = createBlockbench()
+		vi.stubGlobal('document', parentDocument)
+		vi.stubGlobal('Blockbench', blockbench)
+		vi.stubGlobal('AnimUX', undefined)
+
+		const documents: Array<readonly Document[]> = []
+		const unsubscribe = subscribeAnimUxDocuments(current => documents.push([...current]))
+
+		const popoutDocument = {} as Document
+		const service = {
+			subscribeDocuments(listener: (value: readonly Document[]) => void) {
+				listener([parentDocument, popoutDocument])
+				return vi.fn()
+			},
+		}
+		blockbench.emit(ANIM_UX_READY_EVENT, { api: { timeline: service } })
+
+		expect(documents).toEqual([[parentDocument], [parentDocument, popoutDocument]])
+		unsubscribe()
+	})
+
+	it('rebinds once when the service changes and cleans up the latest service', () => {
+		const parentDocument = {} as Document
+		const blockbench = createBlockbench()
+		vi.stubGlobal('document', parentDocument)
+		vi.stubGlobal('Blockbench', blockbench)
+
+		const firstUnsubscribe = vi.fn()
+		const secondUnsubscribe = vi.fn()
+		const firstService = {
+			subscribeDocuments: vi.fn(() => firstUnsubscribe),
+		}
+		const secondService = {
+			subscribeDocuments: vi.fn(() => secondUnsubscribe),
+		}
+		const unsubscribe = subscribeAnimUxDocuments(vi.fn())
+
+		blockbench.emit(ANIM_UX_READY_EVENT, { api: { timeline: firstService } })
+		blockbench.emit(ANIM_UX_READY_EVENT, { api: { timeline: firstService } })
+		blockbench.emit(ANIM_UX_READY_EVENT, { api: { timeline: secondService } })
+		unsubscribe()
+
+		expect(firstService.subscribeDocuments).toHaveBeenCalledOnce()
+		expect(firstUnsubscribe).toHaveBeenCalledOnce()
+		expect(secondService.subscribeDocuments).toHaveBeenCalledOnce()
+		expect(secondUnsubscribe).toHaveBeenCalledOnce()
+	})
+})
diff --git a/src/util/animUxTimeline.ts b/src/util/animUxTimeline.ts
new file mode 100644
index 00000000..e001b752
--- /dev/null
+++ b/src/util/animUxTimeline.ts
@@ -0,0 +1,103 @@
+export const ANIM_UX_READY_EVENT = 'animux:ready'
+
+export type AnimUxDocumentsListener = (documents: readonly Document[]) => void
+
+interface AnimUxTimelineService {
+	subscribeDocuments(listener: AnimUxDocumentsListener): () => void
+}
+
+interface AnimUxApi {
+	timeline: AnimUxTimelineService
+}
+
+interface AnimUxReadyData {
+	api?: unknown
+}
+
+interface BlockbenchEventHost {
+	on(eventName: string, listener: (data: unknown) => void): unknown
+	removeListener(eventName: string, listener: (data: unknown) => void): void
+}
+
+function isRecord(value: unknown): value is Record<string, unknown> {
+	return typeof value === 'object' && value !== null
+}
+
+function asAnimUxApi(value: unknown): AnimUxApi | undefined {
+	if (!isRecord(value) || !isRecord(value.timeline)) return undefined
+	if (typeof value.timeline.subscribeDocuments !== 'function') return undefined
+	return value as unknown as AnimUxApi
+}
+
+function getCurrentApi(): AnimUxApi | undefined {
+	const value = (globalThis as typeof globalThis & { AnimUX?: unknown }).AnimUX
+	return asAnimUxApi(value)
+}
+
+function getBlockbench(): BlockbenchEventHost | undefined {
+	const value = (globalThis as typeof globalThis & { Blockbench?: unknown }).Blockbench
+	if (!isRecord(value)) return undefined
+	if (typeof value.on !== 'function' || typeof value.removeListener !== 'function') return undefined
+	return value as unknown as BlockbenchEventHost
+}
+
+function getReadyApi(data: unknown): AnimUxApi | undefined {
+	if (!isRecord(data)) return undefined
+	return asAnimUxApi((data as AnimUxReadyData).api)
+}
+
+function notifyParentDocument(listener: AnimUxDocumentsListener): void {
+	listener([document])
+}
+
+/**
+ * Tracks the optional anim-ux timeline service and exposes one document stream.
+ * The stream always has a usable parent-document fallback when anim-ux is absent.
+ */
+export function subscribeAnimUxDocuments(listener: AnimUxDocumentsListener): () => void {
+	let currentService: AnimUxTimelineService | undefined
+	let unsubscribeService: (() => void) | undefined
+	let disposed = false
+	let hasBoundService = false
+
+	const bindService = (api: AnimUxApi | undefined): void => {
+		if (disposed) return
+		const nextService = api?.timeline
+		if (hasBoundService && nextService === currentService) return
+
+		unsubscribeService?.()
+		unsubscribeService = undefined
+		currentService = nextService
+		hasBoundService = true
+
+		if (!nextService) {
+			notifyParentDocument(listener)
+			return
+		}
+
+		try {
+			unsubscribeService = nextService.subscribeDocuments(listener)
+		} catch (error) {
+			currentService = undefined
+			notifyParentDocument(listener)
+			console.warn('[AJ] AnimUX timeline subscription failed, using parent document', error)
+		}
+	}
+
+	const onReady = (data: unknown): void => {
+		bindService(getReadyApi(data))
+	}
+
+	const blockbench = getBlockbench()
+	blockbench?.on(ANIM_UX_READY_EVENT, onReady)
+	bindService(getCurrentApi())
+
+	return (): void => {
+		if (disposed) return
+		disposed = true
+		blockbench?.removeListener(ANIM_UX_READY_EVENT, onReady)
+		unsubscribeService?.()
+		unsubscribeService = undefined
+		currentService = undefined
+	}
+}