diff --git a/src/uix/adom/active-dom.svelte.ts b/src/uix/adom/active-dom.svelte.ts
index 203b72d01..704810ebc 100644
--- a/src/uix/adom/active-dom.svelte.ts
+++ b/src/uix/adom/active-dom.svelte.ts
@@ -7,6 +7,7 @@ import {
 	type Breakpoints,
 	type ResponsiveProp
 } from '$uix/lib/dom'
+import { applyChange, removeAttrs, type StructuralChange } from './apply.js'
 import { initViewportTracking, viewport } from './viewport.svelte.js'
 
 export type ActiveDomProps = {
@@ -20,6 +21,8 @@ export type ActiveDom = {
 	resolve<T>(value: ResponsiveProp<T> | undefined): T | undefined
 	isAtLeast(breakpoint: Breakpoint): boolean
 	matches(breakpoint: Breakpoint): boolean
+	apply(change: StructuralChange): void
+	remove(target: HTMLElement, names: readonly string[]): void
 }
 
 const viewportReadonly: { readonly width: number } = {
@@ -52,6 +55,12 @@ export function createActiveDom(props: ActiveDomProps = {}): ActiveDom {
 		},
 		matches(breakpoint: Breakpoint): boolean {
 			return currentBreakpoint.current === breakpoint
+		},
+		apply(change: StructuralChange): void {
+			applyChange(change)
+		},
+		remove(target: HTMLElement, names: readonly string[]): void {
+			removeAttrs(target, names)
 		}
 	}
 }
diff --git a/src/uix/adom/apply.test.ts b/src/uix/adom/apply.test.ts
new file mode 100644
index 000000000..5142b3e4a
--- /dev/null
+++ b/src/uix/adom/apply.test.ts
@@ -0,0 +1,75 @@
+// @vitest-environment jsdom
+
+import { beforeEach, describe, expect, it } from 'vitest'
+
+import { applyChange, removeAttrs } from './apply'
+
+describe('apply', () => {
+	let target: HTMLElement
+
+	beforeEach(() => {
+		document.body.innerHTML = ''
+		target = document.createElement('div')
+		document.body.appendChild(target)
+	})
+
+	it('writes string values via setAttribute', () => {
+		applyChange({ target, attrs: { 'data-state': 'open', role: 'dialog' } })
+		expect(target.getAttribute('data-state')).toBe('open')
+		expect(target.getAttribute('role')).toBe('dialog')
+	})
+
+	it('writes number values stringified', () => {
+		applyChange({ target, attrs: { 'aria-level': 2, tabindex: -1 } })
+		expect(target.getAttribute('aria-level')).toBe('2')
+		expect(target.getAttribute('tabindex')).toBe('-1')
+	})
+
+	it('writes true as empty string (presence flag)', () => {
+		applyChange({ target, attrs: { 'data-disabled': true } })
+		expect(target.hasAttribute('data-disabled')).toBe(true)
+		expect(target.getAttribute('data-disabled')).toBe('')
+	})
+
+	it('removes attribute on false / null / undefined', () => {
+		target.setAttribute('data-disabled', '')
+		target.setAttribute('aria-hidden', 'true')
+		target.setAttribute('data-loading', 'true')
+
+		applyChange({
+			target,
+			attrs: { 'data-disabled': false, 'aria-hidden': null, 'data-loading': undefined }
+		})
+
+		expect(target.hasAttribute('data-disabled')).toBe(false)
+		expect(target.hasAttribute('aria-hidden')).toBe(false)
+		expect(target.hasAttribute('data-loading')).toBe(false)
+	})
+
+	it('removes attrs by name', () => {
+		target.setAttribute('data-event', 'announce')
+		target.setAttribute('data-event-phase', 'active')
+		target.setAttribute('data-state', 'open')
+
+		removeAttrs(target, ['data-event', 'data-event-phase'])
+
+		expect(target.hasAttribute('data-event')).toBe(false)
+		expect(target.hasAttribute('data-event-phase')).toBe(false)
+		expect(target.getAttribute('data-state')).toBe('open')
+	})
+
+	it('mixes write and remove in a single change', () => {
+		target.setAttribute('data-loading', '')
+
+		applyChange({
+			target,
+			attrs: {
+				'data-state': 'open',
+				'data-loading': false
+			}
+		})
+
+		expect(target.getAttribute('data-state')).toBe('open')
+		expect(target.hasAttribute('data-loading')).toBe(false)
+	})
+})
diff --git a/src/uix/adom/apply.ts b/src/uix/adom/apply.ts
new file mode 100644
index 000000000..6298e5c08
--- /dev/null
+++ b/src/uix/adom/apply.ts
@@ -0,0 +1,48 @@
+/**
+ * `apply` / `remove` — the only mutation surface of `ActiveDom`.
+ *
+ * `ActiveDom` doesn't know Morfo, Sema, Soma, or Eidos. It receives instructions
+ * already resolved by upper layers and applies them to the DOM. Nothing else.
+ *
+ * Contract:
+ * - `string | number` → `setAttribute(name, String(value))`
+ * - `true` → `setAttribute(name, '')` (presence flag, e.g. `data-disabled`)
+ * - `false | null | undefined` → `removeAttribute(name)`
+ *
+ * No event dispatch, no batching, no observation. Pure mutations.
+ */
+
+import { isBrowser } from '$uix/lib/dom'
+
+export type DomAttrValue = string | number | boolean | null | undefined
+
+export type StructuralChange = {
+	target: HTMLElement
+	attrs: Record<string, DomAttrValue>
+}
+
+function writeAttr(target: HTMLElement, name: string, value: DomAttrValue): void {
+	if (value === false || value === null || value === undefined) {
+		target.removeAttribute(name)
+		return
+	}
+	if (value === true) {
+		target.setAttribute(name, '')
+		return
+	}
+	target.setAttribute(name, String(value))
+}
+
+export function applyChange(change: StructuralChange): void {
+	if (!isBrowser) return
+	for (const name in change.attrs) {
+		writeAttr(change.target, name, change.attrs[name])
+	}
+}
+
+export function removeAttrs(target: HTMLElement, names: readonly string[]): void {
+	if (!isBrowser) return
+	for (const name of names) {
+		target.removeAttribute(name)
+	}
+}
diff --git a/src/uix/adom/index.ts b/src/uix/adom/index.ts
index 58881bc83..9f496cd2c 100644
--- a/src/uix/adom/index.ts
+++ b/src/uix/adom/index.ts
@@ -1,4 +1,5 @@
 export * from './active-dom.svelte.js'
+export * from './apply.js'
 export * from './body-scroll-lock.svelte.js'
 export * from './dom-context.svelte.js'
 export * from './roving-focus-group.svelte.js'
diff --git a/src/uix/sema/emit.test.ts b/src/uix/sema/emit.test.ts
new file mode 100644
index 000000000..416068545
--- /dev/null
+++ b/src/uix/sema/emit.test.ts
@@ -0,0 +1,125 @@
+// @vitest-environment jsdom
+
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+
+import { createActiveDom } from '$uix/adom'
+import { SemanticEngine } from './engine'
+
+type Frame = () => void
+
+function setupRafQueue() {
+	const queue: Frame[] = []
+	const raf = vi.fn((cb: Frame) => {
+		queue.push(cb)
+		return queue.length
+	}) as unknown as typeof window.requestAnimationFrame
+
+	const flush = () => {
+		const pending = queue.splice(0, queue.length)
+		for (const cb of pending) cb()
+	}
+
+	return { queue, raf, flush }
+}
+
+describe('SemanticEngine.emit', () => {
+	let target: HTMLElement
+	let originalRaf: typeof window.requestAnimationFrame
+	let rafQueue: ReturnType<typeof setupRafQueue>
+
+	beforeEach(() => {
+		document.body.innerHTML = ''
+		target = document.createElement('div')
+		document.body.appendChild(target)
+
+		originalRaf = window.requestAnimationFrame
+		rafQueue = setupRafQueue()
+		window.requestAnimationFrame = rafQueue.raf
+		;(globalThis as { requestAnimationFrame?: typeof window.requestAnimationFrame }).requestAnimationFrame =
+			rafQueue.raf
+	})
+
+	afterEach(() => {
+		window.requestAnimationFrame = originalRaf
+		;(globalThis as { requestAnimationFrame?: typeof window.requestAnimationFrame }).requestAnimationFrame =
+			originalRaf
+	})
+
+	it('throws when constructed without a dom', async () => {
+		const engine = new SemanticEngine()
+		await expect(
+			engine.emit({ target, name: 'announce', family: 'alert', intent: 'risk' })
+		).rejects.toThrow(/requires `dom`/)
+	})
+
+	it('writes signal attrs synchronously, before the frame elapses', () => {
+		const dom = createActiveDom()
+		const engine = new SemanticEngine({ dom })
+
+		void engine.emit({ target, name: 'announce', family: 'alert', intent: 'risk' })
+
+		expect(target.getAttribute('data-event')).toBe('announce')
+		expect(target.getAttribute('data-event-phase')).toBe('active')
+		expect(target.getAttribute('data-event-family')).toBe('alert')
+		expect(target.getAttribute('data-intent')).toBe('risk')
+		expect(target.getAttribute('data-event-id')).toMatch(/^sig-\d+$/)
+	})
+
+	it('resolves only after one rAF', async () => {
+		const dom = createActiveDom()
+		const engine = new SemanticEngine({ dom })
+
+		let resolved = false
+		const promise = engine.emit({ target, name: 'announce' }).then(() => {
+			resolved = true
+		})
+
+		await Promise.resolve()
+		expect(resolved).toBe(false)
+
+		rafQueue.flush()
+		await promise
+		expect(resolved).toBe(true)
+	})
+
+	it('keeps signal in DOM during the hold window after resolving', async () => {
+		const dom = createActiveDom()
+		const engine = new SemanticEngine({ dom })
+
+		await Promise.all([engine.emit({ target, name: 'announce', hold: 2 }), rafQueue.flush()])
+
+		expect(target.getAttribute('data-event')).toBe('announce')
+		// hold=2: cleanup scheduled with 2 frames; first tick decrements to 1
+		rafQueue.flush()
+		expect(target.getAttribute('data-event')).toBe('announce')
+		// second tick decrements to 0 and cleans up
+		rafQueue.flush()
+		expect(target.hasAttribute('data-event')).toBe(false)
+		expect(target.hasAttribute('data-event-phase')).toBe(false)
+		expect(target.hasAttribute('data-event-id')).toBe(false)
+	})
+
+	it('default hold is 1 frame', async () => {
+		const dom = createActiveDom()
+		const engine = new SemanticEngine({ dom })
+
+		const promise = engine.emit({ target, name: 'announce' })
+		rafQueue.flush()
+		await promise
+
+		expect(target.getAttribute('data-event')).toBe('announce')
+		rafQueue.flush()
+		expect(target.hasAttribute('data-event')).toBe(false)
+	})
+
+	it('omits family/intent attrs when not provided', async () => {
+		const dom = createActiveDom()
+		const engine = new SemanticEngine({ dom })
+
+		const promise = engine.emit({ target, name: 'open' })
+		expect(target.hasAttribute('data-event-family')).toBe(false)
+		expect(target.hasAttribute('data-intent')).toBe(false)
+		rafQueue.flush()
+		await promise
+	})
+})
diff --git a/src/uix/sema/engine.ts b/src/uix/sema/engine.ts
index d5c7aa966..d53a6997e 100644
--- a/src/uix/sema/engine.ts
+++ b/src/uix/sema/engine.ts
@@ -1,6 +1,7 @@
 import { DEV } from 'esm-env'
 
 import { normalizeSemaEvent } from './event'
+import type { SemanticSignal } from './signal'
 import type {
 	SemaAttrWrite,
 	SemaCause,
@@ -14,8 +15,39 @@ import type {
 	SemaScope
 } from './types'
 
+import type { ActiveDom } from '$uix/adom'
 import type { PartRef } from '../lib/types'
 
+export interface SemanticEngineOpts {
+	/**
+	 * DOM service injected by construction. Required for `emit()`. The legacy
+	 * `publish()` path still works without it for backward compatibility while
+	 * MorfoRuntime is being rolled out.
+	 */
+	dom?: ActiveDom
+}
+
+function nextFrame(): Promise<void> {
+	return new Promise((resolve) => {
+		if (typeof requestAnimationFrame === 'function') {
+			requestAnimationFrame(() => resolve())
+		} else {
+			setTimeout(resolve, 0)
+		}
+	})
+}
+
+function buildSignalAttrs(signal: SemanticSignal, id: string): Record<string, string> {
+	const attrs: Record<string, string> = {
+		'data-event': signal.name,
+		'data-event-id': id,
+		'data-event-phase': 'active'
+	}
+	if (signal.family) attrs['data-event-family'] = signal.family
+	if (signal.intent) attrs['data-intent'] = signal.intent
+	return attrs
+}
+
 export interface SemanticEventDecl {
 	name: string
 	target: PartRef
@@ -98,7 +130,73 @@ function resolvePartElement(
 
 export class SemanticEngine {
 	private readonly subscribers = new Set<SemanticSubscriber>()
+	private readonly dom: ActiveDom | undefined
 	private nextId = 0
+	private nextSignalId = 0
+
+	constructor(opts: SemanticEngineOpts = {}) {
+		this.dom = opts.dom
+	}
+
+	/**
+	 * Emit a perceptual signal. Resolves after the signal is written to the DOM
+	 * **and** has had one animation frame to be observed by Eidos / CSS. The
+	 * signal is then held for `signal.hold` extra frames (default 1) before
+	 * being cleared.
+	 *
+	 * Sequence:
+	 *   1. write `data-event*` via `dom.apply`
+	 *   2. await 1 rAF
+	 *   3. resolve the Promise (caller can now `dom.apply(structuralChange)`)
+	 *   4. hold N frames
+	 *   5. clear `data-event*`
+	 *
+	 * The cleanup is fire-and-forget: it doesn't block the resolution, and an
+	 * error in the caller's structural change after `await` does not affect it.
+	 */
+	async emit(signal: SemanticSignal): Promise<void> {
+		if (!this.dom) {
+			throw new Error(
+				'[semantic] SemanticEngine.emit requires `dom` to be passed in the constructor.'
+			)
+		}
+
+		const id = `sig-${this.nextSignalId++}`
+		const attrs = buildSignalAttrs(signal, id)
+		const dom = this.dom
+
+		dom.apply({ target: signal.target, attrs })
+		await nextFrame()
+
+		const hold = Math.max(1, signal.hold ?? 1)
+		const names = Object.keys(attrs)
+		this.scheduleCleanup(signal.target, names, hold)
+	}
+
+	private scheduleCleanup(target: HTMLElement, names: readonly string[], holdFrames: number): void {
+		const dom = this.dom
+		if (!dom) return
+
+		let remaining = holdFrames
+		const tick = () => {
+			remaining -= 1
+			if (remaining <= 0) {
+				dom.remove(target, names)
+				return
+			}
+			if (typeof requestAnimationFrame === 'function') {
+				requestAnimationFrame(tick)
+			} else {
+				setTimeout(tick, 16)
+			}
+		}
+
+		if (typeof requestAnimationFrame === 'function') {
+			requestAnimationFrame(tick)
+		} else {
+			setTimeout(tick, 16)
+		}
+	}
 
 	publish(
 		contract: SemanticComponentContract,
diff --git a/src/uix/sema/exports.ts b/src/uix/sema/exports.ts
index 8b9eb6574..702fb9207 100644
--- a/src/uix/sema/exports.ts
+++ b/src/uix/sema/exports.ts
@@ -38,9 +38,12 @@ export type {
 	SemanticComponentContract,
 	SemanticPublishContext,
 	PublishedSemanticEvent,
-	SemanticEventFilter
+	SemanticEventFilter,
+	SemanticEngineOpts
 } from './engine'
 
 export { SemanticEngine } from './engine'
 
+export type { SemanticSignal } from './signal'
+
 export { SemaInvariantError, validateSemaEvent, validateSemaIntentBinding } from './validation'
diff --git a/src/uix/sema/signal.ts b/src/uix/sema/signal.ts
new file mode 100644
index 000000000..16aeb760d
--- /dev/null
+++ b/src/uix/sema/signal.ts
@@ -0,0 +1,31 @@
+/**
+ * SemanticSignal — runtime payload that the provider (or MorfoRuntime) hands
+ * to `EngineSemantic.emit(...)`. Distinct from `SemaEvent`, which describes
+ * the *declaration* of an event in a morfo file (`{ family, intent }`).
+ *
+ * `SemanticSignal` describes the actual occurrence: a target, a name, the
+ * resolved family/intent, and an optional hold duration in animation frames.
+ */
+
+import type { SemaFamily, SemaIntent } from './types'
+
+export interface SemanticSignal {
+	/** DOM target where the perceptual signal is reflected. */
+	target: HTMLElement
+
+	/** Event name as declared in `morfo.events[].name` (e.g. `'close-cancel'`). */
+	name: string
+
+	/** Resolved intent for valenced families. Omit for transitional families. */
+	intent?: SemaIntent
+
+	/** Resolved family. When omitted, only `data-event` and `data-event-id` are written. */
+	family?: SemaFamily
+
+	/**
+	 * Frames the signal stays in the DOM after the Promise resolves.
+	 * Defaults to 1. Components with longer perceptual windows can extend it
+	 * (e.g. announce events that need to "linger" for AT or Eidos animations).
+	 */
+	hold?: number
+}