Same optimization as the merged ResponseMessage PR: replace JSON.parse(JSON.stringify()) with structuredClone and add an O(1) fast-path check on content before falling back to full JSON.stringify comparison.
Same optimization as ResponseMessage: add O(1) fast-path check on content and done fields before falling back to full JSON.stringify comparison. Avoids expensive serialization when only content changes during streaming.
Replace 7 instances of JSON.parse(JSON.stringify()) deep cloning with the native structuredClone API. All are on cold paths (model selection, file preparation, history saving) but structuredClone is ~2x faster and more readable.
During streaming, every token change triggers a full JSON.stringify comparison on the code block token object. Add an O(1) fast-path check on token.text and token.raw — the fields that actually change during streaming — before falling back to the expensive JSON.stringify comparison for infrequent structural changes.
Add O(1) array length check before expensive JSON.stringify comparison. During streaming, status history typically only grows via appends, so a length mismatch catches most updates without serialization.
Messages.svelte rebuilds the message list by walking the parent chain and creating spread copies on every history.messages change. During streaming, this runs on every token — hundreds of times per second — even though each ResponseMessage already has its own reactive binding for content updates. Throttle the rebuild to once per animation frame (~60Hz) during content-only updates, while keeping immediate rebuilds for structural changes (currentId changes like chat switches, navigation, or new messages). Adds onDestroy cleanup for the pending rAF.
