feat: move AI chat history to sidebar and drop in-panel header

- Add an "AI chat" section to the sidebar (mobile drawer, desktop, and
  operator views) showing past chats from HistoryManager with a + button
  in the header that creates a new chat and routes to /design-sandbox.
  Section title fades out when the sidebar is collapsed.
- Remove the in-panel chat header from AIChatDisplay (Chat title,
  HideButton slot, History popover, + button, headerRight slot) along
  with the now-unused props (pastChats, loadPastChat, deletePastChat,
  saveAndClear, headerLeft, headerRight). The chat panel now starts
  directly with the messages, and history/new-chat live in the sidebar.
- AIChat.svelte updated to drop the headerLeft snippet, the HideButton
  import, and the now-unused props on AIChatDisplay.
- design-sandbox page mocks aiChatManager.historyManager.getPastChats()
  with realistic Windmill-style chat titles so the sidebar history is
  populated for the design preview without writing to IndexedDB.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/lib/components/copilot/chat/AIChat.svelte

@@ -5,7 +5,6 @@
 	import { dbSchemas, userStore, workspaceStore } from '$lib/stores'
 	import { aiChatManager, AIMode } from './AIChatManager.svelte'
 	import { base } from '$lib/base'
-	import HideButton from '$lib/components/apps/editor/settingsPanel/HideButton.svelte'
 	import { SUPPORTED_CHAT_SCRIPT_LANGUAGES } from './script/core'
 	import { copilotInfo, copilotSessionModel } from '$lib/aiStore'
 
@@ -53,8 +52,6 @@
 		aiChatManager.sendRequest(options)
 	}
 
-	const historyManager = aiChatManager.historyManager
-
 	let aiChatDisplay: AIChatDisplay | undefined = $state(undefined)
 
 	$effect(() => {
@@ -80,20 +77,8 @@
 	}}
 />
 
-{#snippet headerLeft()}
-	<HideButton
-		hidden={false}
-		direction="right"
-		panelName="AI"
-		shortcut="L"
-		size="md"
-		on:click={() => aiChatManager.toggleOpen()}
-	/>
-{/snippet}
-
 <AIChatDisplay
 	bind:this={aiChatDisplay}
-	pastChats={historyManager.getPastChats()}
 	bind:selectedContext={
 		() => aiChatManager.contextManager.getSelectedContext(),
 		(sc) => aiChatManager.contextManager.setSelectedContext(sc)
@@ -113,16 +98,8 @@
 				}
 			]
 		: aiChatManager.displayMessages}
-	saveAndClear={aiChatManager.saveAndClear}
-	deletePastChat={(id) => {
-		historyManager.deletePastChat(id)
-	}}
-	loadPastChat={(id) => {
-		aiChatManager.loadPastChat(id)
-	}}
 	cancel={aiChatManager.cancel}
 	askAi={aiChatManager.askAi}
-	{headerLeft}
 	hasDiff={aiChatManager.scriptEditorOptions &&
 		!!aiChatManager.scriptEditorOptions.lastDeployedCode &&
 		aiChatManager.scriptEditorOptions.lastDeployedCode !== aiChatManager.scriptEditorOptions.code}

frontend/src/lib/components/copilot/chat/AIChatDisplay.svelte

@@ -1,22 +1,18 @@
 <script lang="ts">
 	import AIChatMessage from './AIChatMessage.svelte'
-	import { type Snippet } from 'svelte'
 	import {
 		ArrowUp,
 		CheckIcon,
 		Code2,
 		FileCode,
-		HistoryIcon,
 		Loader2,
 		MousePointer2,
-		Plus,
 		Square,
 		TextSelect,
 		X,
 		XIcon
 	} from 'lucide-svelte'
 	import Button from '$lib/components/common/button/Button.svelte'
-	import Popover from '$lib/components/meltComponents/Popover.svelte'
 	import { type DisplayMessage } from './shared'
 	import type { ContextElement } from './context'
 	import ChatQuickActions from './ChatQuickActions.svelte'
@@ -31,35 +27,23 @@
 
 	let {
 		messages,
-		pastChats,
 		hasDiff,
 		diffMode = false, // todo: remove default
 		selectedContext = $bindable([]), // todo: remove default
 		availableContext = [], // todo: remove default
-		loadPastChat,
-		deletePastChat,
-		saveAndClear,
 		cancel,
 		askAi = () => {}, // todo: remove default,
-		headerLeft,
-		headerRight,
 		disabled = false,
 		disabledMessage = '',
 		suggestions = []
 	}: {
 		messages: DisplayMessage[]
-		pastChats: { id: string; title: string }[]
 		hasDiff?: boolean
 		diffMode: boolean
 		selectedContext: ContextElement[]
 		availableContext: ContextElement[]
-		loadPastChat: (id: string) => void
-		deletePastChat: (id: string) => void
-		saveAndClear: () => void
 		cancel: () => void
 		askAi?: (instructions: string, options?: { withCode?: boolean; withDiff?: boolean }) => void
-		headerLeft?: Snippet
-		headerRight?: Snippet
 		disabled?: boolean
 		disabledMessage?: string
 		suggestions?: string[]
@@ -113,80 +97,6 @@
 </script>
 
 <div class="flex flex-col h-full">
-	<div
-		class="flex flex-row items-center justify-between gap-2 p-2 border-b border-gray-200 dark:border-gray-600"
-	>
-		<div class="flex flex-row items-center gap-2">
-			{@render headerLeft?.()}
-			<p class="text-sm font-semibold">Chat</p>
-		</div>
-		<div class="flex flex-row items-center gap-2">
-			<Popover>
-				{#snippet trigger()}
-					<Button
-						on:click={() => {}}
-						title="History"
-						size="md"
-						btnClasses="!p-1"
-						startIcon={{ icon: HistoryIcon }}
-						iconOnly
-						variant="border"
-						color="light"
-						propagateEvent
-					/>
-				{/snippet}
-				{#snippet content({ close })}
-					<div class="p-1 overflow-y-auto max-h-[300px]">
-						{#if pastChats.length === 0}
-							<div class="text-center text-primary text-xs">No history</div>
-						{:else}
-							<div class="flex flex-col">
-								{#each pastChats as chat}
-									<button
-										class="text-left flex flex-row items-center gap-2 justify-between hover:bg-gray-100 dark:hover:bg-gray-700 rounded-md p-1"
-										onclick={() => {
-											loadPastChat(chat.id)
-											close()
-										}}
-									>
-										<div
-											class="text-xs font-medium w-48 text-ellipsis overflow-hidden whitespace-nowrap flex-1"
-											title={chat.title}
-										>
-											{chat.title}
-										</div>
-										<Button
-											iconOnly
-											size="xs2"
-											btnClasses="!p-1"
-											variant="default"
-											startIcon={{ icon: X }}
-											on:click={() => {
-												deletePastChat(chat.id)
-											}}
-										/>
-									</button>
-								{/each}
-							</div>
-						{/if}
-					</div>
-				{/snippet}
-			</Popover>
-			<Button
-				title="New chat"
-				on:click={() => {
-					saveAndClear()
-				}}
-				size="md"
-				btnClasses="!p-1"
-				startIcon={{ icon: Plus }}
-				iconOnly
-				variant="border"
-				color="light"
-			/>
-			{@render headerRight?.()}
-		</div>
-	</div>
 	{#if messages.length === 0}
 		<span class="text-2xs text-gray-500 dark:text-gray-400 text-center px-2 my-2"
 			>You can use {getModifierKey()}L to open or close this chat, and {getModifierKey()}K in the

frontend/src/routes/(root)/(logged)/+layout.svelte

@@ -49,7 +49,7 @@
 	import { SUPERADMIN_SETTINGS_HASH, USER_SETTINGS_HASH } from '$lib/components/sidebar/settings'
 	import { isCloudHosted } from '$lib/cloud'
 	import { syncTutorialsTodos } from '$lib/tutorialUtils'
-	import { ArrowLeft, Search, WandSparkles } from 'lucide-svelte'
+	import { ArrowLeft, Plus, Search, WandSparkles } from 'lucide-svelte'
 	import { getUserExt } from '$lib/user'
 	import { deepEqual } from 'fast-equals'
 	import { twMerge } from 'tailwind-merge'
@@ -463,6 +463,49 @@
 	globalDbManagerDrawer.val = useDbManagerUriState()
 </script>
 
+{#snippet chatHistorySection({ isCollapsed: collapsed }: { isCollapsed: boolean })}
+	<div class="pt-3 flex flex-col">
+		<div class="flex flex-row items-center justify-between px-2 mb-1">
+			<div
+				class="text-secondary text-[0.5rem] uppercase transition-opacity"
+				class:opacity-0={collapsed}
+			>
+				AI chat
+			</div>
+			<button
+				type="button"
+				title="New chat"
+				class="p-0.5 rounded text-secondary hover:bg-surface-hover hover:text-primary transition-colors"
+				onclick={() => {
+					aiChatManager.saveAndClear()
+					goto('/design-sandbox')
+				}}
+			>
+				<Plus class="w-3.5 h-3.5" />
+			</button>
+		</div>
+		{#if !collapsed}
+			<div class="flex flex-col gap-1.5 max-h-48 overflow-y-auto">
+				{#each aiChatManager.historyManager.getPastChats() as chat (chat.id)}
+					<button
+						type="button"
+						class="text-left text-2xs font-normal px-2 py-1.5 rounded hover:bg-surface-hover transition-colors truncate"
+						title={chat.title}
+						onclick={() => {
+							aiChatManager.loadPastChat(chat.id)
+							goto('/design-sandbox')
+						}}
+					>
+						{chat.title}
+					</button>
+				{:else}
+					<div class="text-2xs font-normal text-secondary px-2 py-1.5 italic">No past chats</div>
+				{/each}
+			</div>
+		{/if}
+	</div>
+{/snippet}
+
 <svelte:window bind:innerWidth />
 
 <UserSettings bind:this={userSettings} showMcpMode={true} />
@@ -576,6 +619,7 @@
 											iconClasses="!text-ai"
 											shortcut={`${getModifierKey()}L`}
 										/>
+										{@render chatHistorySection({ isCollapsed: false })}
 									</div>
 
 									<SidebarContent
@@ -655,6 +699,7 @@
 									iconClasses="!text-ai"
 									shortcut={`${getModifierKey()}L`}
 								/>
+								{@render chatHistorySection({ isCollapsed })}
 							</div>
 
 							<SidebarContent
@@ -768,6 +813,7 @@
 									iconClasses="!text-ai"
 									shortcut={`${getModifierKey()}L`}
 								/>
+								{@render chatHistorySection({ isCollapsed })}
 							</div>
 
 							<SidebarContent

frontend/src/routes/(root)/(logged)/design-sandbox/+page.svelte

@@ -85,6 +85,19 @@
 		}
 	]
 
+	// Realistic-sounding past-chat titles for the sidebar history. Just titles + ids
+	// because the sidebar snippet only reads those two fields.
+	const fakePastChats = [
+		{ id: 'mock_1', title: 'Daily user re-engagement flow' },
+		{ id: 'mock_2', title: 'Sync Stripe customers to Postgres' },
+		{ id: 'mock_3', title: 'Weekly usage report email' },
+		{ id: 'mock_4', title: 'Migrate S3 bucket to GCS' },
+		{ id: 'mock_5', title: 'Slack alert on failed deploys' },
+		{ id: 'mock_6', title: 'Parse CSV uploads into Postgres' },
+		{ id: 'mock_7', title: 'Generate signed download URLs' },
+		{ id: 'mock_8', title: 'Onboarding webhook handler' }
+	]
+
 	function applyMocks() {
 		// Pretend Windmill AI is enabled with an Anthropic model so the chat input is active.
 		copilotInfo.set({
@@ -96,6 +109,11 @@
 		})
 		aiChatManager.mode = AIMode.FLOW
 		aiChatManager.displayMessages = fakeMessages
+
+		// Patch getPastChats so the sidebar's "AI chat" history shows the mock titles
+		// without writing anything to IndexedDB (keeps the real workspace history clean).
+		// Cast to any because savedChats / pastChats are private fields on HistoryManager.
+		;(aiChatManager.historyManager as any).getPastChats = () => fakePastChats
 	}
 
 	// The parent (logged) layout always renders its AiChatLayout (right-side chat).