fix(ui): prevent shiki template-call OOM on backtick JS

Neutralize the catastrophic TextMate template-call lookahead when loading
JS/TS grammars in the markdown Shiki worker, and terminate hung highlight
requests after 5s so unbounded Oniguruma WASM matching cannot OOM the
renderer (openchamber/openchamber#2587).

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

packages/ui/src/components/chat/markdown/markdown-shiki.worker.ts

@@ -1,6 +1,10 @@
 /// <reference lib="webworker" />
 
-import { bundledLanguages, createHighlighter, type BundledLanguage, type ThemedToken } from 'shiki';
+import { bundledLanguages, createHighlighter, type BundledLanguage, type LanguageRegistration, type ThemedToken } from 'shiki';
+import {
+  isTemplateCallLanguageId,
+  sanitizeTemplateCallGrammar,
+} from '../../../lib/shiki/sanitizeTemplateCallGrammar';
 import { MARKDOWN_SHIKI_THEME, MARKDOWN_SHIKI_THEME_DEFINITION } from './markdownShikiThemeDefinition';
 import type { MarkdownWorkerRequest, MarkdownWorkerResponse } from './markdown-worker-protocol';
 
@@ -60,11 +64,28 @@ self.onmessage = (event: MessageEvent<MarkdownWorkerRequest>) => {
 
 type Instance = Awaited<ReturnType<typeof createHighlighter>>;
 
+type BundledLanguageModule = { default: LanguageRegistration[] };
+
+/**
+ * Load a language, neutralizing the catastrophic JS/TS `template-call` rule
+ * before it reaches the Oniguruma scanner (see sanitizeTemplateCallGrammar).
+ */
+const loadLanguageSafe = async (instance: Instance, lang: BundledLanguage): Promise<void> => {
+  if (!isTemplateCallLanguageId(lang)) {
+    await instance.loadLanguage(bundledLanguages[lang]);
+    return;
+  }
+
+  const mod = (await bundledLanguages[lang]()) as BundledLanguageModule;
+  const grammars = mod.default.map((grammar) => sanitizeTemplateCallGrammar(grammar));
+  await instance.loadLanguage(...grammars);
+};
+
 const resolveLanguage = async (instance: Instance, requested: string): Promise<string> => {
   let lang = requested in bundledLanguages ? requested : 'text';
   if (lang !== 'text' && !instance.getLoadedLanguages().includes(lang)) {
     try {
-      await instance.loadLanguage(bundledLanguages[lang as BundledLanguage]);
+      await loadLanguageSafe(instance, lang as BundledLanguage);
     } catch {
       lang = 'text';
     }

packages/ui/src/components/chat/markdown/markdown-worker-timeout.ts

@@ -0,0 +1,6 @@
+/**
+ * Safety-net budget for a single Shiki worker tokenize request.
+ * Healthy files finish well under this; catastrophic Oniguruma backtracking
+ * must not run unbounded (openchamber/openchamber#2587).
+ */
+export const HIGHLIGHT_REQUEST_TIMEOUT_MS = 5_000;

packages/ui/src/components/chat/markdown/markdown-worker.hang.test.ts

@@ -0,0 +1,12 @@
+import { describe, expect, test } from 'bun:test';
+
+import { HIGHLIGHT_REQUEST_TIMEOUT_MS } from './markdown-worker-timeout';
+
+describe('markdown-worker hang safety', () => {
+  test('exposes a finite highlight timeout budget', () => {
+    // Catastrophic Oniguruma backtracking must not run unbounded; the main
+    // thread terminates the worker after this budget (openchamber/openchamber#2587).
+    expect(HIGHLIGHT_REQUEST_TIMEOUT_MS).toBeGreaterThan(0);
+    expect(HIGHLIGHT_REQUEST_TIMEOUT_MS).toBeLessThan(15_001);
+  });
+});

packages/ui/src/components/chat/markdown/markdown-worker.ts

@@ -1,23 +1,42 @@
 import MarkdownShikiWorkerUrl from './markdown-shiki.worker.ts?worker&url';
 import type { MarkdownTokenRun, MarkdownWorkerRequest, MarkdownWorkerResponse } from './markdown-worker-protocol';
+import { HIGHLIGHT_REQUEST_TIMEOUT_MS } from './markdown-worker-timeout';
 
-// Main-thread client for the markdown Shiki worker. Moves syntax tokenization
+export { HIGHLIGHT_REQUEST_TIMEOUT_MS } from './markdown-worker-timeout';
+
+// Main-thread client for the markdown Shiki Web Worker. Moves syntax tokenization
 // off the UI thread: a closed code block is shipped to the worker, which returns
 // ready-to-splice Shiki HTML. On any failure (no worker support, worker crash,
-// tokenization error) the promise resolves to `null` and the caller keeps the
-// escaped plain-text code — highlighting never falls back onto the main thread.
+// tokenization error, or hang timeout) the promise resolves to `null` and the
+// caller keeps the escaped plain-text code — highlighting never falls back onto
+// the main thread.
+//
+// The timeout exists because TextMate grammars can enter catastrophic backtracking
+// on the Oniguruma WASM engine (openchamber/openchamber#2587). Matching is sync
+// inside the worker, so the only way to reclaim memory is to terminate it from
+// this thread when a request exceeds the budget.
 
 type PendingResolver = (response: MarkdownWorkerResponse | null) => void;
 
+type PendingEntry = {
+  resolve: PendingResolver;
+  timer: ReturnType<typeof setTimeout>;
+};
+
 let worker: Worker | undefined;
 let nextId = 0;
-const pending = new Map<number, PendingResolver>();
+const pending = new Map<number, PendingEntry>();
 // Theme names whose full definition we've already shipped to the live worker, so
 // repeat tokenization sends only the name (not the whole theme object) again.
 const sentThemes = new Set<string>();
 
+const clearPendingTimers = (): void => {
+  pending.forEach((entry) => clearTimeout(entry.timer));
+};
+
 const failAll = (): void => {
-  pending.forEach((resolve) => resolve(null));
+  clearPendingTimers();
+  pending.forEach((entry) => entry.resolve(null));
   pending.clear();
   sentThemes.clear();
   worker?.terminate();
@@ -34,10 +53,11 @@ const getWorker = (): Worker | undefined => {
     return undefined;
   }
   worker.onmessage = (event: MessageEvent<MarkdownWorkerResponse>) => {
-    const resolve = pending.get(event.data.id);
-    if (!resolve) return;
+    const entry = pending.get(event.data.id);
+    if (!entry) return;
+    clearTimeout(entry.timer);
     pending.delete(event.data.id);
-    resolve(event.data);
+    entry.resolve(event.data);
   };
   worker.onerror = failAll;
   worker.onmessageerror = failAll;
@@ -50,7 +70,14 @@ const request = (payload: (id: number) => MarkdownWorkerRequest): Promise<Markdo
   if (!instance) return Promise.resolve(null);
   const id = ++nextId;
   return new Promise<MarkdownWorkerResponse | null>((resolve) => {
-    pending.set(id, resolve);
+    const timer = setTimeout(() => {
+      if (!pending.has(id)) return;
+      // Hung tokenize (e.g. catastrophic backtracking): kill the worker so the
+      // WASM heap is freed instead of growing until the renderer OOMs.
+      console.warn(`Shiki worker highlight timed out after ${HIGHLIGHT_REQUEST_TIMEOUT_MS}ms; terminating worker`);
+      failAll();
+    }, HIGHLIGHT_REQUEST_TIMEOUT_MS);
+    pending.set(id, { resolve, timer });
     instance.postMessage(payload(id));
   });
 };

packages/ui/src/lib/shiki/sanitizeTemplateCallGrammar.test.ts

@@ -0,0 +1,75 @@
+import { describe, expect, test } from 'bun:test';
+import { bundledLanguages, createHighlighter, type LanguageRegistration } from 'shiki';
+
+import {
+  hasCatastrophicTemplateCall,
+  isTemplateCallLanguageId,
+  sanitizeTemplateCallGrammar,
+  TEMPLATE_CALL_LANGUAGE_IDS,
+} from './sanitizeTemplateCallGrammar';
+
+type BundledLanguageModule = { default: LanguageRegistration[] };
+
+const loadBundledGrammar = async (id: (typeof TEMPLATE_CALL_LANGUAGE_IDS)[number]): Promise<LanguageRegistration> => {
+  const mod = (await bundledLanguages[id]()) as BundledLanguageModule;
+  return mod.default[0];
+};
+
+describe('sanitizeTemplateCallGrammar', () => {
+  test('detects template-call on bundled JS/TS grammars', async () => {
+    for (const id of TEMPLATE_CALL_LANGUAGE_IDS) {
+      const grammar = await loadBundledGrammar(id);
+      expect(isTemplateCallLanguageId(id)).toBe(true);
+      expect(hasCatastrophicTemplateCall(grammar)).toBe(true);
+    }
+  });
+
+  test('clears template-call patterns without dropping the repository key', async () => {
+    const grammar = await loadBundledGrammar('javascript');
+    const patched = sanitizeTemplateCallGrammar(grammar);
+
+    expect(hasCatastrophicTemplateCall(patched)).toBe(false);
+    expect(patched.repository?.['template-call']).toEqual({ patterns: [] });
+    // Original left intact (structured clone / spread, not mutate-in-place).
+    expect(hasCatastrophicTemplateCall(grammar)).toBe(true);
+  });
+
+  test('is a no-op when template-call is already empty', () => {
+    const grammar = {
+      name: 'javascript',
+      scopeName: 'source.js',
+      patterns: [],
+      repository: { 'template-call': { patterns: [] } },
+    } satisfies LanguageRegistration;
+    expect(sanitizeTemplateCallGrammar(grammar)).toBe(grammar);
+  });
+
+  test('highlights template-literal fixtures within a tight budget after sanitize', async () => {
+    const mod = (await bundledLanguages.javascript()) as BundledLanguageModule;
+    const patched = mod.default.map((grammar) => sanitizeTemplateCallGrammar(grammar));
+
+    const highlighter = await createHighlighter({
+      themes: ['github-dark'],
+      langs: patched,
+    });
+
+    // Representative content from openchamber/openchamber#2587, scaled to ~14KB.
+    const fixture = `const snapshot = { source: \`\${session.source}\`, fetchedAt: \`\${Date.now()}\` };
+const label = \`Account \${index + 1}\`;
+function render(account) {
+  return html\`<div class="\${account.cls}">\${account.name}</div>\`;
+}
+`.repeat(80);
+
+    expect(fixture.length).toBeGreaterThan(10_000);
+
+    const started = performance.now();
+    const html = highlighter.codeToHtml(fixture, { lang: 'javascript', theme: 'github-dark' });
+    const elapsedMs = performance.now() - started;
+    highlighter.dispose();
+
+    expect(html.length).toBeGreaterThan(0);
+    // Catastrophic backtracking hangs for seconds–minutes; healthy tokenize is well under 1s.
+    expect(elapsedMs).toBeLessThan(2_000);
+  });
+});

packages/ui/src/lib/shiki/sanitizeTemplateCallGrammar.ts

@@ -0,0 +1,45 @@
+/**
+ * Neutralize the JavaScript/TypeScript TextMate `template-call` rule.
+ *
+ * Upstream grammars use a triple-nested `{()[]}` lookahead to detect tagged
+ * templates with type arguments (`foo<T>\`...\``). On the Oniguruma WASM engine
+ * shipped with Shiki — which does not expose `setRetryLimit` / match-stack
+ * limits — that pattern can enter exponential backtracking on ordinary
+ * backtick template literals, grow the WASM heap without bound, and OOM the
+ * renderer (openchamber/openchamber#2587).
+ *
+ * Clearing `template-call` is safe: the plain `#template` rule still highlights
+ * backticks and simple tagged templates. Only the rare `ident<TypeArgs>\`...\``
+ * form loses its specialized type-argument coloring and falls through to
+ * normal tokenization.
+ */
+
+type GrammarRepository = Record<string, { patterns?: unknown[] } | undefined>;
+
+export type TemplateCallGrammar = {
+  name?: string;
+  repository?: GrammarRepository;
+};
+
+const TEMPLATE_CALL_KEY = 'template-call';
+
+export const hasCatastrophicTemplateCall = (grammar: TemplateCallGrammar): boolean => {
+  const patterns = grammar.repository?.[TEMPLATE_CALL_KEY]?.patterns;
+  return Array.isArray(patterns) && patterns.length > 0;
+};
+
+export const sanitizeTemplateCallGrammar = <T extends TemplateCallGrammar>(grammar: T): T => {
+  if (!hasCatastrophicTemplateCall(grammar)) return grammar;
+
+  const repository = { ...grammar.repository };
+  repository[TEMPLATE_CALL_KEY] = { patterns: [] };
+  return { ...grammar, repository };
+};
+
+/** Language ids whose bundled grammars ship the catastrophic `template-call` rule. */
+export const TEMPLATE_CALL_LANGUAGE_IDS = ['javascript', 'typescript', 'jsx', 'tsx'] as const;
+
+export type TemplateCallLanguageId = (typeof TEMPLATE_CALL_LANGUAGE_IDS)[number];
+
+export const isTemplateCallLanguageId = (lang: string): lang is TemplateCallLanguageId =>
+  (TEMPLATE_CALL_LANGUAGE_IDS as readonly string[]).includes(lang);