【BUG】Desktop renderer becomes unresponsive when Home preloads very large markdown sessions

[xu-xiaofei]

Description

I hit an intermittent Desktop UI freeze (renderer unresponsive) on Windows when opening the Home page.

Observed on OpenCode 1.18.7 (Windows x64).
In exported debug logs (opencode-debug-20260729T072406.zip), the hot stack repeatedly points to markdown preloading/parsing:

• RegExp.exec
• marked lexer
• preloadMarkdown (oc://renderer/assets/main-*.js)

This appears to block the renderer main thread during Home preloading.

Local data scale that can trigger it:

• Total sessions: 109
• Total text parts: 3615
• Largest single text block: 1,653,459 chars
• One heavy recent session has 801 text parts (max block 91,041 chars)

Plugins

No response

OpenCode version

1.18.7

Steps to reproduce

1. Use Desktop app on Windows.
2. Have recent sessions containing very large markdown content (or one session with hundreds of text parts).
3. Open the Home page (which preloads recent sessions).
4. Wait a few seconds; UI may become unresponsive.
5. Export logs and check window.log for repeated renderer unresponsive samples pointing to preloadMarkdown / marked lexer.

Screenshot and/or share link

No response

Operating System

Windows 10 (10.0.19045) x64

Terminal

Windows Terminal (not relevant for this Desktop UI freeze)

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• Desktop: renderer unresponsive on startup — marked.js walkTokens synchronous Markdown AST traversal blocks UI thread #32452: Desktop renderer unresponsive on startup due to synchronous marked.js Markdown AST traversal blocking the UI thread — same symptom (renderer unresponsive, marked lexer in stack trace, Windows x64 Desktop app)

[xu-xiaofei]

Rebased onto latest dev, ready for review.