The opencode Desktop UI freezes for approximately 10–12 seconds when rendering file diffs. #31195

Description

The opencode Desktop UI freezes for approximately 10–12 seconds when rendering file diffs. During the freeze the window becomes unresponsive and the OS may show a "not responding" warning.

To Reproduce

1. Open a session with a file diff visible in the conversation (e.g., after a tool edit or a write operation)
2. The UI freezes for ~10–12 seconds
3. The window recovers on its own

Expected behavior

The UI should remain responsive. Diff rendering should be asynchronous or yield to the event loop so the renderer does not block.

Stack trace (from window.log)

renderer unresponsive { window: 'main', currentURL: 'oc://renderer/index.html' }
renderer responsive { window: 'main', currentURL: 'oc://renderer/index.html' }
renderer unresponsive samples (12 samples)

    at execEditLength (oc://renderer/assets/main-EPcHbCKO.js:42291:7)
    at LineDiff.diffWithOptionsObj (oc://renderer/assets/main-EPcHbCKO.js:42340:21)
    at LineDiff.diff (oc://renderer/assets/main-EPcHbCKO.js:42261:17)
    at diffLines (oc://renderer/assets/main-EPcHbCKO.js:42491:19)
    at structuredPatch (oc://renderer/assets/main-EPcHbCKO.js:42529:35)
    at createTwoFilesPatch (oc://renderer/assets/main-EPcHbCKO.js:42656:22)
    at parseDiffFromFile (oc://renderer/assets/main-EPcHbCKO.js:44283:32)
    at fileDiffFromContent (oc://renderer/assets/session-CGwfdNgW.js:18980:10)
    at fileDiffFromPatch (oc://renderer/assets/session-CGwfdNgW.js:18914:28)
    at resolveFileDiff (oc://renderer/assets/session-CGwfdNgW.js:18884:47)

The call chain shows a synchronous diff computation (execEditLength → structuredPatch → createTwoFilesPatch) that blocks the SolidJS reactive graph, freezing the UI.

Additional context

The freeze is consistently reproducible when viewing diffs. The diff library being used appears to compute the LCS/edit distance synchronously on the main thread without yielding. Potential mitigations:

1. Offload large diffs to a Web Worker or use requestIdleCallback
2. Virtualize or truncate very large diffs
3. Use a streaming diff implementation that yields periodically

Plugins

No response

OpenCode version

1.16.2

Steps to reproduce

When I type a question, when I open OpenCode Desktop, or out of nowhere, OpenCode freezes for about 10 or 15 seconds.

Screenshot and/or share link

No response

Operating System

Windows 11 x64

Terminal

No response