diff --git a/frontend/src/lib/components/DropdownSubmenuItem.svelte b/frontend/src/lib/components/DropdownSubmenuItem.svelte
index 60f7ad2d64..a67411a039 100644
--- a/frontend/src/lib/components/DropdownSubmenuItem.svelte
+++ b/frontend/src/lib/components/DropdownSubmenuItem.svelte
@@ -13,9 +13,10 @@
 		item: Item
 		builders: ReturnType<typeof createDropdownMenu>['builders']
 		meltItem: MenubarMenuElements['item']
+		close?: (afterClose?: () => void) => void
 	}
 
-	let { item, builders, meltItem }: Props = $props()
+	let { item, builders, meltItem, close }: Props = $props()
 
 	const {
 		elements: { subTrigger, subMenu },
@@ -23,6 +24,8 @@
 	} = untrack(() => builders).createSubmenu()
 
 	let subItems = $derived((item.submenuItems ?? []).filter((i) => !i.hide))
+	const CustomSubmenu = $derived(item.customSubmenu)
+	const closeMenu = $derived(close ?? (() => {}))
 </script>
 
 <button
@@ -46,14 +49,20 @@
 {#if $subOpen}
 	<div
 		use:melt={$subMenu}
-		class="z-[6000] bg-surface-tertiary dark:border w-48 origin-top-right rounded-lg shadow-lg focus:outline-none overflow-y-auto py-1"
+		class="z-[6000] bg-surface-tertiary dark:border {CustomSubmenu
+			? ''
+			: 'w-48 overflow-y-auto py-1'} origin-top-right rounded-lg shadow-lg focus:outline-none"
 	>
-		{#each subItems as subItem}
-			{#if subItem.separatorTop}
-				<div class="my-1 border-t border-border-light"></div>
-			{/if}
-			{@render subMenuItem(subItem)}
-		{/each}
+		{#if CustomSubmenu}
+			<CustomSubmenu {...item.customSubmenuProps} close={closeMenu} />
+		{:else}
+			{#each subItems as subItem}
+				{#if subItem.separatorTop}
+					<div class="my-1 border-t border-border-light"></div>
+				{/if}
+				{@render subMenuItem(subItem)}
+			{/each}
+		{/if}
 	</div>
 {/if}
 
diff --git a/frontend/src/lib/components/DropdownV2.svelte b/frontend/src/lib/components/DropdownV2.svelte
index 5061636835..1d86519293 100644
--- a/frontend/src/lib/components/DropdownV2.svelte
+++ b/frontend/src/lib/components/DropdownV2.svelte
@@ -132,8 +132,9 @@
 		})
 	})
 
-	export function close() {
+	export function close(afterClose?: () => void) {
 		open = false
+		if (afterClose) setTimeout(afterClose, 10)
 	}
 
 	async function computeItems(): Promise<Item[]> {
@@ -209,7 +210,7 @@
 				class="bg-surface-tertiary dark:border w-56 origin-top-right rounded-lg shadow-lg focus:outline-none overflow-y-auto py-1"
 				style={`${customWidth ? `width: ${customWidth}px;` : ''} max-height: ${maxHeight || '50vh'};`}
 			>
-				<DropdownV2Inner {aiId} items={computeItems} meltItem={item} {builders} />
+				<DropdownV2Inner {aiId} items={computeItems} meltItem={item} {builders} {close} />
 			</div>
 		{/if}
 	</div>
diff --git a/frontend/src/lib/components/DropdownV2Inner.svelte b/frontend/src/lib/components/DropdownV2Inner.svelte
index 7749310b5b..31fd9426f5 100644
--- a/frontend/src/lib/components/DropdownV2Inner.svelte
+++ b/frontend/src/lib/components/DropdownV2Inner.svelte
@@ -13,9 +13,10 @@
 		items?: Item[] | (() => Item[]) | (() => Promise<Item[]>)
 		meltItem: MenubarMenuElements['item']
 		builders?: ReturnType<typeof createDropdownMenu>['builders']
+		close?: (afterClose?: () => void) => void
 	}
 
-	let { aiId, items = [], meltItem, builders }: Props = $props()
+	let { aiId, items = [], meltItem, builders, close }: Props = $props()
 
 	let computedItems: Item[] | undefined = $state(undefined)
 	async function computeItems() {
@@ -102,8 +103,8 @@
 			{#if item.separatorTop}
 				<div class="my-1 border-t border-border-light"></div>
 			{/if}
-			{#if item.submenuItems && builders}
-				<DropdownSubmenuItem {item} {builders} {meltItem} />
+			{#if (item.submenuItems || item.customSubmenu) && builders}
+				<DropdownSubmenuItem {item} {builders} {meltItem} close={close ?? (() => {})} />
 			{:else if item.disabled && item.tooltip}
 				<!-- Wrapper carries the native `title`; the disabled button's `pointer-events-none`
 				     lets the hover reach it so the user learns why the item is disabled. -->
diff --git a/frontend/src/lib/components/copilot/chat/AIChatDisplay.svelte b/frontend/src/lib/components/copilot/chat/AIChatDisplay.svelte
index cf27a45d89..17d752ae39 100644
--- a/frontend/src/lib/components/copilot/chat/AIChatDisplay.svelte
+++ b/frontend/src/lib/components/copilot/chat/AIChatDisplay.svelte
@@ -3,6 +3,7 @@
 	import AIChatMessage from './AIChatMessage.svelte'
 	import AppAvailableContextList from './AppAvailableContextList.svelte'
 	import ChatContextPicker from './ChatContextPicker.svelte'
+	import WorkspaceMentionPicker from './WorkspaceMentionPicker.svelte'
 	import { type Snippet } from 'svelte'
 	import {
 		AlertTriangle,
@@ -548,6 +549,11 @@
 		await imageWork
 	}
 
+	function mentionWorkspaceItem(element: ContextElement) {
+		void aiChatInput?.addContextToSelection(element)
+		aiChatInput?.insertMention(element.title)
+	}
+
 	function onFolderInputChange(e: Event) {
 		const input = e.currentTarget as HTMLInputElement
 		// webkitdirectory files carry webkitRelativePath (`folder/sub/file`); addFiles groups
@@ -1055,6 +1061,19 @@ the panel, or the Escape-to-stop focus check would wrongly reject them. -->
 													}
 												]
 											: []),
+										...(inGlobal
+											? [
+													{
+														displayName: 'Mention file',
+														icon: AtSign,
+														customSubmenu: WorkspaceMentionPicker,
+														customSubmenuProps: {
+															onSelect: mentionWorkspaceItem,
+															onAfterClose: () => aiChatInput?.focusInput()
+														}
+													}
+												]
+											: []),
 										...(skillItems
 											? [
 													{
diff --git a/frontend/src/lib/components/copilot/chat/AIChatInput.svelte b/frontend/src/lib/components/copilot/chat/AIChatInput.svelte
index 6f15937cf2..bcea3a26d6 100644
--- a/frontend/src/lib/components/copilot/chat/AIChatInput.svelte
+++ b/frontend/src/lib/components/copilot/chat/AIChatInput.svelte
@@ -14,7 +14,7 @@
 	import { CHAT_INPUT_PADDING, getAiChatManager } from './aiChatManagerContext'
 	import { getChatViewHost } from './chatViewHost'
 	import { composerBoxClass, COMPOSER_FIELD_RESET } from './composerBox'
-	import { formatMention } from './mention'
+	import { formatMention, hasMention, removeMentionFromText } from './mention'
 	import { twMerge } from 'tailwind-merge'
 	import { tick, untrack, type Snippet } from 'svelte'
 	import Portal from '$lib/components/Portal.svelte'
@@ -588,40 +588,33 @@
 
 	const contextKey = contextElementKey
 
-	/** Append `@title` to the textarea so the button-picker path stays in
-	 * sync with the inline `@<word>` mention path — both leave a visible
-	 * token tied to the selectedContext entry, which the textarea diffs on
-	 * to auto-remove items when the user deletes them. No-op when the
-	 * mention is already present so re-picking the same item doesn't
-	 * leave duplicate tokens. */
+	/** Insert `@title` so button/menu picker paths stay in sync with
+	 * the inline `@<word>` mention path — both leave a visible token tied
+	 * to the selectedContext entry, which the textarea diffs on to
+	 * auto-remove items when the user deletes them. No-op when the same
+	 * standalone mention is already present, so picking the same item
+	 * again doesn't leave duplicate tokens. */
 	export function insertMention(title: string) {
-		const target = `@${title}`
-		if (draft.text.split(/\s+/).includes(target)) return
+		if (hasMention(draft.text, title)) return
+		if (contextTextareaComponent) {
+			void contextTextareaComponent.insertMention(title)
+			return
+		}
 		const sep = draft.text.length === 0 || /\s$/.test(draft.text) ? '' : ' '
-		draft.text = `${draft.text}${sep}${target} `
+		draft.text = `${draft.text}${sep}${formatMention(title)} `
 	}
 
 	/** Strip every `@title` token from the textarea — used when the user
 	 * deletes the corresponding badge so the badge X-button mirrors the
-	 * inverse (text-delete-to-badge-remove) sync. Only matches `@title` as a
-	 * standalone token (boundary on both sides) so substring matches don't
-	 * bleed into other words; only the whitespace adjacent to the removed
-	 * mention is collapsed so unrelated double-spaces stay intact. */
+	 * inverse (text-delete-to-badge-remove) sync. Only matches tokens whose
+	 * `@` starts a word, so embedded text like `owner@app.ts` is left alone
+	 * while punctuation and non-spacing text after the token still work. */
 	export function removeMention(title: string) {
 		// Pre-zap the textarea's mention diff snapshot so the upcoming strip
 		// doesn't refire the removal effect on a same-title sibling — the host
 		// has already mutated `selectedContext` to drop the targeted entry.
 		contextTextareaComponent?.unsyncMention(title)
-		const escaped = title.replace(/[.*+?^${}()|[\]\\]/g, '\\$&')
-		const re = new RegExp(`(^|\\s)@${escaped}(\\s|$)`, 'g')
-		draft.text = draft.text.replace(re, (_m, lead, trail) => {
-			// Boundary on at least one side → drop the mention entirely.
-			if (!lead || !trail) return ''
-			// Middle of text: keep ONE of the bracketing whitespace chars so
-			// the surviving tokens are still separated; preserve the leading
-			// one verbatim so newlines/tabs aren't downgraded to spaces.
-			return lead
-		})
+		draft.text = removeMentionFromText(draft.text, title)
 	}
 
 	export function focusInput() {
diff --git a/frontend/src/lib/components/copilot/chat/ContextTextarea.svelte b/frontend/src/lib/components/copilot/chat/ContextTextarea.svelte
index 976b969b3f..dd3a011da2 100644
--- a/frontend/src/lib/components/copilot/chat/ContextTextarea.svelte
+++ b/frontend/src/lib/components/copilot/chat/ContextTextarea.svelte
@@ -10,7 +10,13 @@
 	import { zIndexes } from '$lib/zIndexes'
 	import { twMerge } from 'tailwind-merge'
 	import { CHAT_INPUT_PADDING, getAiChatManager } from './aiChatManagerContext'
-	import { MENTION_RE, mentionTitle, formatMention } from './mention'
+	import {
+		MENTION_RE,
+		mentionTitle,
+		formatMention,
+		hasMentionLeadingBoundary,
+		mentionTitlesInText
+	} from './mention'
 	import { createFloatingActions, createVirtualElement } from 'svelte-floating-ui'
 	import { flip, offset, shift } from 'svelte-floating-ui/dom'
 	import {
@@ -65,17 +71,11 @@
 
 	const aiChatManager = getAiChatManager()
 
-	function extractMentions(text: string): Set<string> {
-		const out = new Set<string>()
-		for (const m of text.matchAll(MENTION_RE)) out.add(mentionTitle(m[0]))
-		return out
-	}
-
 	// Titles currently appearing as `@title` mentions in the textarea. Compared
 	// against the previous snapshot in a $effect (NOT inside handleInput —
 	// the picker mutates `value` programmatically via `updateInstructionsWithContext`,
 	// which doesn't fire `oninput`, so a handleInput-only diff goes stale).
-	const mentionedTitles = $derived(extractMentions(value))
+	const mentionedTitles = $derived(mentionTitlesInText(value))
 	let prevMentionedTitles = $state<Set<string>>(new Set())
 
 	let showContextTooltip = $state(false)
@@ -268,7 +268,11 @@
 			if (!att) return match
 			return `<span data-paste-id="${att.id}" class="rounded bg-surface-secondary text-secondary cursor-pointer pointer-events-auto">${match}</span>`
 		})
-		html = html.replace(MENTION_RE, (match) => {
+		html = html.replace(MENTION_RE, (match, ...args) => {
+			const offset = args[args.length - 2]
+			if (typeof offset !== 'number' || !hasMentionLeadingBoundary(html, offset)) {
+				return match
+			}
 			const title = unescapeHtml(mentionTitle(match))
 			const inContext =
 				availableContext.find((c) => c.title === title) ||
@@ -566,6 +570,23 @@
 		showContextTooltip = false
 	}
 
+	export async function insertMention(title: string) {
+		const token = formatMention(title)
+		const selectionStart = textarea?.selectionStart ?? value.length
+		const selectionEnd = textarea?.selectionEnd ?? selectionStart
+		const { from, to, ids } = tokensOverlapping(selectionStart, selectionEnd)
+		const before = value.slice(0, from)
+		const after = value.slice(to)
+		const prefix = before.length === 0 || /\s$/.test(before) ? '' : ' '
+		const suffix = after.length === 0 ? ' ' : /^\s/.test(after) ? '' : ' '
+		const inserted = `${prefix}${token}${suffix}`
+		replacePasteRange(from, to, ids, inserted)
+		await tick()
+		const pos = from + inserted.length
+		textarea?.setSelectionRange(pos, pos)
+		textarea?.focus()
+	}
+
 	function refreshCommandSkills() {
 		if (commandSkillsRefreshInFlight) return
 		commandSkillsRefreshInFlight = true
diff --git a/frontend/src/lib/components/copilot/chat/WorkspaceMentionPicker.svelte b/frontend/src/lib/components/copilot/chat/WorkspaceMentionPicker.svelte
new file mode 100644
index 0000000000..0fb21f684f
--- /dev/null
+++ b/frontend/src/lib/components/copilot/chat/WorkspaceMentionPicker.svelte
@@ -0,0 +1,148 @@
+<!--
+@component
+Workspace-only picker for the AI session composer's `+ -> Mention file`
+submenu. It mirrors ChatContextPicker's workspace branch, but starts directly
+at the workspace root because the parent menu item already names the scope.
+-->
+<script lang="ts">
+	import { Folder } from 'lucide-svelte'
+	import RowIcon from '$lib/components/common/table/RowIcon.svelte'
+	import DrillPicker from '$lib/components/DrillPicker.svelte'
+	import type { DrillBranch, DrillLeaf, DrillNode } from '$lib/components/drillPicker'
+	import {
+		workspaceItemDisplayPath,
+		type WorkspaceItem,
+		type WorkspaceItemKind
+	} from '$lib/components/workspacePicker'
+	import { useWorkspaceItemsLoader } from '$lib/components/workspaceItemsLoader.svelte'
+	import { buildWorkspaceTree, relativizeWorkspacePath } from '$lib/components/workspaceTree'
+	import { useOperatingWorkspace } from '$lib/components/operatingWorkspace.svelte'
+	import type {
+		ContextElement,
+		WorkspaceAppElement,
+		WorkspaceFlowElement,
+		WorkspaceScriptElement
+	} from './context'
+
+	interface Props {
+		onSelect: (element: ContextElement) => void
+		onAfterClose?: () => void
+		close: (afterClose?: () => void) => void
+	}
+
+	type DrillPickerHandle = {
+		handleKeydown: (e: KeyboardEvent) => void
+	}
+
+	let { onSelect, onAfterClose, close }: Props = $props()
+	let picker: DrillPickerHandle | undefined = $state()
+
+	const operatingWorkspace = useOperatingWorkspace()
+	const WORKSPACE_KINDS: WorkspaceItemKind[] = ['flow', 'script', 'app']
+	const loader = useWorkspaceItemsLoader(
+		() => $operatingWorkspace,
+		() => WORKSPACE_KINDS
+	)
+
+	const loadedForTree = $derived.by(() => {
+		const loaded = loader.loaded
+		if (!loaded.app) return loaded
+		return { ...loaded, app: loaded.app.filter((a) => a.raw_app) }
+	})
+
+	const tree = $derived<DrillNode<WorkspaceItem>[]>(
+		buildWorkspaceTree({
+			loaded: loadedForTree,
+			kinds: WORKSPACE_KINDS,
+			loadingKind: loader.loadingKind,
+			layout: 'flat'
+		}) as DrillNode<WorkspaceItem>[]
+	)
+
+	function workspaceElement(item: WorkspaceItem): ContextElement | undefined {
+		if (item.kind === 'script') {
+			return {
+				type: 'workspace_script',
+				path: item.path,
+				title: item.path,
+				summary: item.summary,
+				deletable: true
+			} satisfies WorkspaceScriptElement & { deletable: boolean }
+		}
+		if (item.kind === 'flow') {
+			return {
+				type: 'workspace_flow',
+				path: item.path,
+				title: item.path,
+				summary: item.summary,
+				deletable: true
+			} satisfies WorkspaceFlowElement & { deletable: boolean }
+		}
+		if (item.kind === 'app') {
+			return {
+				type: 'workspace_app',
+				path: item.path,
+				title: item.path,
+				summary: item.summary,
+				deletable: true
+			} satisfies WorkspaceAppElement & { deletable: boolean }
+		}
+	}
+
+	function handlePick(leaf: DrillLeaf<WorkspaceItem>) {
+		const element = workspaceElement(leaf.data)
+		if (!element) return
+		onSelect(element)
+		close(onAfterClose)
+	}
+
+	function handleScopeChange(_scope: string[]) {
+		loader.ensureAll()
+	}
+
+	const pickerKeys = new Set([
+		'ArrowDown',
+		'ArrowUp',
+		'ArrowLeft',
+		'ArrowRight',
+		'Backspace',
+		'Enter',
+		'Tab',
+		'Home',
+		'End'
+	])
+
+	function handleKeydownCapture(e: KeyboardEvent) {
+		if (!pickerKeys.has(e.key)) return
+		e.stopImmediatePropagation()
+		picker?.handleKeydown(e)
+	}
+</script>
+
+{#snippet leafIcon(leaf: DrillLeaf<WorkspaceItem>)}
+	<RowIcon kind={leaf.data.kind} size={12} />
+{/snippet}
+
+{#snippet branchIcon(branch: DrillBranch<WorkspaceItem>)}
+	{#if branch.icon}
+		{@const Icon = branch.icon}
+		<Icon size={12} class="shrink-0 text-tertiary" />
+	{:else}
+		<Folder size={12} class="shrink-0 text-tertiary" />
+	{/if}
+{/snippet}
+
+<!-- Capture picker-owned keys before Melt's submenu listener handles menu movement. -->
+<div onkeydowncapture={handleKeydownCapture}>
+	<DrillPicker
+		bind:this={picker}
+		{tree}
+		onPick={handlePick}
+		{leafIcon}
+		{branchIcon}
+		leafSecondary={(leaf, scope) => relativizeWorkspacePath(workspaceItemDisplayPath(leaf.data), scope)}
+		onScopeChange={handleScopeChange}
+		onFilterChange={loader.onFilterChange}
+		rootLoading={WORKSPACE_KINDS.some((k) => !loader.loaded[k] && loader.loadingKind[k])}
+	/>
+</div>
diff --git a/frontend/src/lib/components/copilot/chat/mention.test.ts b/frontend/src/lib/components/copilot/chat/mention.test.ts
index 8d379ce3b4..ae021bf1de 100644
--- a/frontend/src/lib/components/copilot/chat/mention.test.ts
+++ b/frontend/src/lib/components/copilot/chat/mention.test.ts
@@ -1,5 +1,12 @@
 import { describe, expect, it } from 'vitest'
-import { MENTION_RE, mentionTitle, formatMention } from './mention'
+import {
+	MENTION_RE,
+	mentionTitle,
+	formatMention,
+	hasMention,
+	mentionTitlesInText,
+	removeMentionFromText
+} from './mention'
 
 describe('formatMention', () => {
 	it('leaves a simple name bare', () => {
@@ -52,3 +59,83 @@ describe('MENTION_RE', () => {
 		expect(mentionTitle(m[0])).toBe(name)
 	})
 })
+
+describe('removeMentionFromText', () => {
+	it('removes a bare mention and keeps neighboring words separated', () => {
+		expect(removeMentionFromText('before @app.ts after', 'app.ts')).toBe('before after')
+	})
+
+	it('removes a bracketed mention', () => {
+		expect(removeMentionFromText('before @[my folder/a b.ts] after', 'my folder/a b.ts')).toBe(
+			'before after'
+		)
+	})
+
+	it('removes an escaped bracketed mention', () => {
+		expect(removeMentionFromText('before @[notes \\] draft.md] after', 'notes ] draft.md')).toBe(
+			'before after'
+		)
+	})
+
+	it('removes edge mentions without leaving extra whitespace', () => {
+		expect(removeMentionFromText('@app.ts after', 'app.ts')).toBe('after')
+		expect(removeMentionFromText('before @app.ts', 'app.ts')).toBe('before')
+	})
+
+	it('keeps embedded mention-like text intact', () => {
+		expect(removeMentionFromText('Contact owner@app.ts about @app.ts', 'app.ts')).toBe(
+			'Contact owner@app.ts about'
+		)
+	})
+
+	it('keeps Unicode-prefixed embedded mention-like text intact', () => {
+		expect(removeMentionFromText('Contact 用户@app.ts about @app.ts', 'app.ts')).toBe(
+			'Contact 用户@app.ts about'
+		)
+		expect(removeMentionFromText('Contact हिंदी@app.ts about @app.ts', 'app.ts')).toBe(
+			'Contact हिंदी@app.ts about'
+		)
+		expect(removeMentionFromText('Contact 𐐀@app.ts about @app.ts', 'app.ts')).toBe(
+			'Contact 𐐀@app.ts about'
+		)
+	})
+})
+
+describe('hasMention', () => {
+	it('does not treat embedded mention-like text as a selected context mention', () => {
+		expect(hasMention('Contact owner@app.ts', 'app.ts')).toBe(false)
+		expect(hasMention('Contact owner@app.ts about @app.ts', 'app.ts')).toBe(true)
+	})
+
+	it('does not treat Unicode-prefixed embedded text as a mention', () => {
+		expect(hasMention('Contact 用户@app.ts', 'app.ts')).toBe(false)
+		expect(hasMention('Contact हिंदी@app.ts', 'app.ts')).toBe(false)
+		expect(hasMention('Contact 𐐀@app.ts', 'app.ts')).toBe(false)
+	})
+
+	it('treats punctuation next to a mention as a boundary', () => {
+		expect(hasMention('use @app.ts, then compare', 'app.ts')).toBe(true)
+		expect(hasMention('open (@app.ts)', 'app.ts')).toBe(true)
+	})
+})
+
+describe('mentionTitlesInText', () => {
+	it('extracts only standalone mentions for context synchronization', () => {
+		expect([...mentionTitlesInText('Contact owner@app.ts about @app.ts')]).toEqual(['app.ts'])
+		expect([...mentionTitlesInText('Contact owner@app.ts')]).toEqual([])
+	})
+
+	it('ignores Unicode-prefixed embedded text for context synchronization', () => {
+		expect([...mentionTitlesInText('Contact 用户@app.ts')]).toEqual([])
+	})
+
+	it('keeps punctuation-adjacent mentions synchronized', () => {
+		expect([...mentionTitlesInText('use @app.ts, then compare')]).toEqual(['app.ts'])
+		expect([...mentionTitlesInText('open (@app.ts)')]).toEqual(['app.ts'])
+	})
+
+	it('ignores combining-mark and astral-letter embedded text', () => {
+		expect([...mentionTitlesInText('Contact हिंदी@app.ts')]).toEqual([])
+		expect([...mentionTitlesInText('Contact 𐐀@app.ts')]).toEqual([])
+	})
+})
diff --git a/frontend/src/lib/components/copilot/chat/mention.ts b/frontend/src/lib/components/copilot/chat/mention.ts
index 65a2b3b7c6..d1d42696b0 100644
--- a/frontend/src/lib/components/copilot/chat/mention.ts
+++ b/frontend/src/lib/components/copilot/chat/mention.ts
@@ -29,3 +29,59 @@ const BARE_SAFE = /^[\w/.\-]+$/
 export function formatMention(name: string): string {
 	return BARE_SAFE.test(name) ? `@${name}` : `@[${name.replace(/[\\\]]/g, '\\$&')}]`
 }
+
+function isWordChar(char: string | undefined): boolean {
+	return char !== undefined && /[\p{L}\p{N}\p{M}_]/u.test(char)
+}
+
+function codePointBefore(text: string, index: number): string | undefined {
+	if (index <= 0) return undefined
+	const prev = text.charCodeAt(index - 1)
+	if (prev >= 0xdc00 && prev <= 0xdfff && index > 1) return text.slice(index - 2, index)
+	return text[index - 1]
+}
+
+// A mention is owned by this parser when the `@` starts a token. The trailing side is
+// intentionally open: non-spacing scripts often continue immediately after a mention,
+// while embedded forms like `owner@app.ts` are rejected by the leading boundary.
+export function hasMentionLeadingBoundary(text: string, index: number): boolean {
+	return !isWordChar(codePointBefore(text, index))
+}
+
+export function isStandaloneMention(text: string, match: RegExpMatchArray): boolean {
+	if (match.index === undefined) return false
+	return hasMentionLeadingBoundary(text, match.index)
+}
+
+export function hasMention(text: string, title: string): boolean {
+	return [...text.matchAll(MENTION_RE)].some(
+		(m) => mentionTitle(m[0]) === title && isStandaloneMention(text, m)
+	)
+}
+
+export function mentionTitlesInText(text: string): Set<string> {
+	const out = new Set<string>()
+	for (const m of text.matchAll(MENTION_RE)) {
+		if (isStandaloneMention(text, m)) out.add(mentionTitle(m[0]))
+	}
+	return out
+}
+
+export function removeMentionFromText(text: string, title: string): string {
+	let out = ''
+	let last = 0
+	for (const m of text.matchAll(MENTION_RE)) {
+		if (m.index === undefined || mentionTitle(m[0]) !== title) continue
+		let start = m.index
+		let end = m.index + m[0].length
+		if (!isStandaloneMention(text, m)) continue
+		const hasLead = start > 0 && /\s/.test(text[start - 1])
+		const hasTrail = end < text.length && /\s/.test(text[end])
+		if (hasLead && !hasTrail) start -= 1
+		if (!hasLead && hasTrail) end += 1
+		if (hasLead && hasTrail) end += 1
+		out += text.slice(last, start)
+		last = end
+	}
+	return out + text.slice(last)
+}
diff --git a/frontend/src/lib/utils.ts b/frontend/src/lib/utils.ts
index 0f9eb78da4..b90751b9d3 100644
--- a/frontend/src/lib/utils.ts
+++ b/frontend/src/lib/utils.ts
@@ -1677,6 +1677,8 @@ export type Item = {
 	iconColor?: string
 	/** Extra props for `icon`, for an icon that does not take lucide's `size`. */
 	iconProps?: Record<string, any>
+	customSubmenu?: import('svelte').Component<any>
+	customSubmenuProps?: Record<string, unknown>
 	href?: string
 	hrefTarget?: '_blank' | '_self' | '_parent' | '_top'
 	disabled?: boolean