Summary

• keep markdown rendering consistent between web and desktop so the same streamed response no longer settles differently depending on where the user reads it
• stop the active assistant response from using paint containment while it is still growing, which removes the flash users were seeing when new markdown landed
• keep the last stable markdown on screen until newer parsing finishes, then make unfinished code fences render in a lighter streaming path so code blocks stay readable and copy buttons keep working during long responses

Testing

• bun typecheck (in packages/ui)
• bun typecheck (in packages/app)