ui: Agentic Content UX improvements (#25450)

* feat: Add shimmer text animation for processing state indicators

* feat: Redesign CollapsibleContentBlock component with improved UX

* feat: Add conditional setting display support with dependsOn field

* feat: Add showAgenticTurnStats setting for per-turn statistics

* feat: Update ChatMessageAgenticContent with improved UI and new features

* feat: Enhance file read tool UI/UX

* feat: Refine styling of collapsible content and code preview blocks

* feat: add terminal variant to CollapsibleContentBlock

* feat: add built-in tools UI registry

* feat: extract ChatMessageReasoningBlock and ChatMessageToolCallBlock

* refactor: simplify ChatMessageAgenticContent to use extracted blocks

* fix: correct markdown content block margin spacing

* fix: reorganize SettingsChatFields layout and reset button positioning

* fix: use direct map access in agentic store session methods

* refactor: remove reasoning preview/throttle system from CollapsibleContentBlock

* feat: add auto-scroll to reasoning block and remove showThoughtInProgress

* feat: add ChatMessageToolCallDateTime component and support for new tool types

* feat: improve auto-scroll reliability in reasoning block with RAF coalescing and MutationObserver

* feat: show MCP server favicon for tools without a built-in icon

* feat: add search-results parsing utilities and tests

* feat: add ChatMessageToolCallSearchResults component

* feat: integrate search results rendering into ChatMessageAgenticContent

* feat: display tool call input alongside output in ChatMessageToolCallBlock

* style: use muted foreground color in reasoning block content

* chore: Format

* feat: Refine reasoning block layout and make pending thoughts display configurable

* feat: Stream tool call code blocks with auto-scroll and handle partial JSON

* feat: add streaming permission gate infrastructure

* feat: wire permission gate into the agentic loop

* fix: bail out on abort and skip already-approved tool calls

* fix: clear partial tool calls on abort and savePartialResponse

* test: cover partial tool call cleanup end-to-end

* refactor: Remove streaming permission gate logic

* fix: Correct autoscroll and streaming gates for tool calls and reasoning blocks

* refactor: Chat Message Assistant componentization

* fix: Show health metadata for disabled MCP servers and promote connections on enable

* fix: Inherit global enabled state for missing MCP per-chat overrides

* refactor: Cleanup

* refactor: Split ChatMessageToolCallBlock into dedicated components

* feat: Add live streaming and auto-scroll for tool execution output

* feat: Add line numbers and change markers to file edit diffs

* chore: Formatting

* feat: Add type definitions and utilities for recommended MCP servers

* feat: Add recommended MCP servers configuration and storage key

* feat: Add McpServerCardCompact component for recommended servers

* feat: Add recommended servers section to Add New Server dialog

* feat: Update McpServerForm to support authorization requirements

* feat: Add select-none classes for text selection prevention

* feat: Add recommended MCP server icon assets

* refactor: Store dismissed MCP recommendations as a boolean flag

* feat: Render tool results as JSON or Markdown based on detected content type

* feat: UI improvement

* feat: Render search block early and update heading to show execution state

* fix: Prevent non-web-search tools from triggering the search UI block

* refactor: Cleanup

* refactor: Extract hardcoded icon size classes into shared constants

* refactor: Extract hardcoded tool result separator into a shared constant

* refactor: Tool Calls UI/logic

* refactor: Cleanup

* refactor: Cleanup

* refactor: Cleanup

tools/ui/src/lib/components/app/content/SyntaxHighlightedCode.svelte

@@ -1,11 +1,12 @@
 <script lang="ts">
-	import hljs from 'highlight.js';
 	import { browser } from '$app/environment';
 	import { mode } from 'mode-watcher';
 
 	import githubDarkCss from 'highlight.js/styles/github-dark.css?inline';
 	import githubLightCss from 'highlight.js/styles/github.css?inline';
 	import { ColorMode } from '$lib/enums';
+	import { SYNTAX_CODE_SCROLL_AT_BOTTOM_THRESHOLD_PX } from '$lib/constants/auto-scroll';
+	import { highlightCode } from '$lib/utils';
 
 	interface Props {
 		code: string;
@@ -13,6 +14,9 @@
 		class?: string;
 		maxHeight?: string;
 		maxWidth?: string;
+		/** Auto-scrolls to the bottom of new chunks; pauses on user scroll-up
+		 *  until the user returns to the bottom. */
+		streaming?: boolean;
 	}
 
 	let {
@@ -20,10 +24,17 @@
 		language = 'text',
 		class: className = '',
 		maxHeight = '60vh',
-		maxWidth = ''
+		maxWidth = '',
+		streaming = false
 	}: Props = $props();
 
-	let highlightedHtml = $state('');
+	const highlightedHtml = $derived(highlightCode(code, language));
+
+	let scrollEl = $state<HTMLDivElement>();
+	let userScrolledUp = $state(false);
+	let lastScrollTop = 0;
+	const SCROLL_BOTTOM_THRESHOLD_PX = SYNTAX_CODE_SCROLL_AT_BOTTOM_THRESHOLD_PX;
+	let pendingFrame: number | null = null;
 
 	function loadHighlightTheme(isDark: boolean) {
 		if (!browser) return;
@@ -38,6 +49,36 @@
 		document.head.appendChild(style);
 	}
 
+	function isAtBottom(): boolean {
+		if (!scrollEl) return false;
+		return (
+			scrollEl.scrollHeight - scrollEl.clientHeight - scrollEl.scrollTop <=
+			SCROLL_BOTTOM_THRESHOLD_PX
+		);
+	}
+
+	function scrollToBottomOnFrame() {
+		if (pendingFrame !== null || !scrollEl || userScrolledUp) return;
+		pendingFrame = requestAnimationFrame(() => {
+			pendingFrame = null;
+			// User may scroll between scheduling and paint.
+			if (scrollEl && !userScrolledUp) {
+				scrollEl.scrollTop = scrollEl.scrollHeight;
+			}
+		});
+	}
+
+	function handleScrollEvent() {
+		if (!scrollEl) return;
+		const isScrollingUp = scrollEl.scrollTop < lastScrollTop;
+		if (isScrollingUp && !isAtBottom()) {
+			userScrolledUp = true;
+		} else if (isAtBottom()) {
+			userScrolledUp = false;
+		}
+		lastScrollTop = scrollEl.scrollTop;
+	}
+
 	$effect(() => {
 		const currentMode = mode.current;
 		const isDark = currentMode === ColorMode.DARK;
@@ -45,46 +86,64 @@
 		loadHighlightTheme(isDark);
 	});
 
+	// Pin to bottom at the start of each streaming episode.
 	$effect(() => {
-		if (!code) {
-			highlightedHtml = '';
-			return;
+		if (streaming) {
+			userScrolledUp = false;
+			lastScrollTop = 0;
 		}
+	});
 
-		try {
-			// Check if the language is supported
-			const lang = language.toLowerCase();
-			const isSupported = hljs.getLanguage(lang);
+	$effect(() => {
+		void code;
+		if (!streaming || userScrolledUp) return;
+		scrollToBottomOnFrame();
+	});
 
-			if (isSupported) {
-				const result = hljs.highlight(code, { language: lang });
-				highlightedHtml = result.value;
-			} else {
-				// Try auto-detection or fallback to plain text
-				const result = hljs.highlightAuto(code);
-				highlightedHtml = result.value;
-			}
-		} catch {
-			// Fallback to escaped plain text
-			highlightedHtml = code.replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;');
-		}
+	// Layout shifts that don't change `code` (highlight.js re-tokenize, line-wrap reflow).
+	$effect(() => {
+		if (!streaming || !scrollEl) return;
+
+		const observer = new MutationObserver(() => scrollToBottomOnFrame());
+		observer.observe(scrollEl, {
+			childList: true,
+			subtree: true,
+			characterData: true
+		});
+
+		return () => observer.disconnect();
 	});
 </script>
 
 <div
-	class="code-preview-wrapper min-w-0 max-w-full overflow-x-auto rounded-lg border border-border bg-muted {className}"
-	style="max-height: {maxHeight}; {maxWidth ? `max-width: ${maxWidth};` : ''}"
+	bind:this={scrollEl}
+	onscroll={handleScrollEvent}
+	class="code-preview-wrapper min-w-0 max-w-full overflow-auto rounded-xl border shadow-[0_1px_2px_0_rgb(0_0_0_/_0.05)] {className}"
+	style="border-color: color-mix(in oklch, var(--border) 30%, transparent); background: var(--code-background); max-height: {maxHeight}; {maxWidth
+		? `max-width: ${maxWidth};`
+		: ''}"
 >
-	<!-- Needs to be formatted as single line for proper rendering -->
+	<!-- Single line: hljs injection depends on a contiguous source string. -->
 	<pre class="m-0"><code class="hljs text-sm leading-relaxed">{@html highlightedHtml}</code></pre>
 </div>
 
 <style>
+	.code-preview-wrapper {
+		overscroll-behavior: contain;
+	}
+
 	.code-preview-wrapper pre {
 		background: transparent;
+		padding: 0;
 	}
 
 	.code-preview-wrapper code {
 		background: transparent;
+		display: block;
+		padding: 0.5rem;
+	}
+
+	:global(.dark) .code-preview-wrapper {
+		border-color: color-mix(in oklch, var(--border) 20%, transparent);
 	}
 </style>