WebUI Architecture Cleanup (#19541)

* webui: architecture foundation (non-MCP core refactors)

* chore: update webui build output

tools/server/webui/src/lib/utils/code.ts

@@ -0,0 +1,85 @@
+import hljs from 'highlight.js';
+import {
+	NEWLINE,
+	DEFAULT_LANGUAGE,
+	LANG_PATTERN,
+	AMPERSAND_REGEX,
+	LT_REGEX,
+	GT_REGEX,
+	FENCE_PATTERN
+} from '$lib/constants/code';
+
+export interface IncompleteCodeBlock {
+	language: string;
+	code: string;
+	openingIndex: number;
+}
+
+/**
+ * Highlights code using highlight.js
+ * @param code - The code to highlight
+ * @param language - The programming language
+ * @returns HTML string with syntax highlighting
+ */
+export function highlightCode(code: string, language: string): string {
+	if (!code) return '';
+
+	try {
+		const lang = language.toLowerCase();
+		const isSupported = hljs.getLanguage(lang);
+
+		if (isSupported) {
+			return hljs.highlight(code, { language: lang }).value;
+		} else {
+			return hljs.highlightAuto(code).value;
+		}
+	} catch {
+		// Fallback to escaped plain text
+		return code
+			.replace(AMPERSAND_REGEX, '&')
+			.replace(LT_REGEX, '<')
+			.replace(GT_REGEX, '>');
+	}
+}
+
+/**
+ * Detects if markdown ends with an incomplete code block (opened but not closed).
+ * Returns the code block info if found, null otherwise.
+ * @param markdown - The raw markdown string to check
+ * @returns IncompleteCodeBlock info or null
+ */
+export function detectIncompleteCodeBlock(markdown: string): IncompleteCodeBlock | null {
+	// Count all code fences in the markdown
+	// A code block is incomplete if there's an odd number of ``` fences
+	const fencePattern = new RegExp(FENCE_PATTERN.source, FENCE_PATTERN.flags);
+	const fences: number[] = [];
+	let fenceMatch;
+
+	while ((fenceMatch = fencePattern.exec(markdown)) !== null) {
+		// Store the position after the ```
+		const pos = fenceMatch[0].startsWith(NEWLINE) ? fenceMatch.index + 1 : fenceMatch.index;
+		fences.push(pos);
+	}
+
+	// If even number of fences (including 0), all code blocks are closed
+	if (fences.length % 2 === 0) {
+		return null;
+	}
+
+	// Odd number means last code block is incomplete
+	// The last fence is the opening of the incomplete block
+	const openingIndex = fences[fences.length - 1];
+	const afterOpening = markdown.slice(openingIndex + 3);
+
+	// Extract language and code content
+	const langMatch = afterOpening.match(LANG_PATTERN);
+	const language = langMatch?.[1] || DEFAULT_LANGUAGE;
+	const codeStartIndex = openingIndex + 3 + (langMatch?.[0]?.length ?? 0);
+	const code = markdown.slice(codeStartIndex);
+
+	return {
+		language,
+		code,
+		openingIndex
+	};
+}