Tokenize closed code blocks in a dedicated Shiki Web Worker instead of calling
the shared highlighter synchronously on the UI thread. This removes the
one-shot main-thread highlight stall when a code fence closes on a large block.
Streaming behavior is unchanged: the open (streaming) fence still renders as
plain text and is highlighted once on close. On any worker failure the block
keeps its escaped plain code — highlighting never falls back onto the main
thread.
- Add markdownShikiThemeDefinition (dependency-free CSS-variable theme) so the
worker can use the theme without pulling in @pierre/diffs / React.
- Add markdown-worker-protocol, markdown-shiki.worker, and the main-thread
markdown-worker client.
- Route highlightCodeBlocks through the worker; keep the size/VSCode line guard
and mermaid skip on the main thread.
- Add shiki as a direct dependency (was transitive via @pierre/diffs).
Bohdan Triapitsyn
464c4ac0ca