## Why
Streaming TUI responses repeatedly rendered the entire accumulated Markdown source for each committed delta, including blocks whose output could no longer change.
## What changed
- Retain rendered output for completed top-level Markdown blocks and rerender only the final mutable block as new source arrives.
- Track block boundaries during the existing Markdown parser pass and map them through table-fence normalization.
- Preserve canonical full rendering when source-wide state may affect earlier output, including reference link definitions and inline visualizations, and when the width or render mode changes.
- Append raw-mode lines directly while preserving blank lines.
## Testing
Added coverage that compares incremental output with full rendering across paragraphs, headings, lists, block quotes, code fences, tables, HTML blocks, links, visualizations, render-mode changes, and normalized table fences.
GitOrigin-RevId: 748171c4ed58923329b59c48ea3c2afa4819ec88
537e69ab66