The transcript viewport draws every frame. Ratatui's Line::render_ref
does grapheme segmentation and span layout, so repeated redraws can burn
CPU during streaming even when the visible transcript hasn't changed.
Introduce TranscriptViewCache to reduce per-frame work:
- WrappedTranscriptCache memoizes flattened+wrapped transcript lines per
width, appends incrementally as new cells arrive, and rebuilds on width
change, truncation (backtrack), or transcript replacement.
- TranscriptRasterCache caches rasterized rows (Vec<Cell>) per line
index and user-row styling; redraws copy cells instead of rerendering
spans.
The caches are width-scoped and store base transcript content only;
selection highlighting and copy affordances are applied after drawing.
User rows include the row-wide base style in the cached raster.
Refactor transcript_render to expose append_wrapped_transcript_cell for
incremental building and add a test that incremental append matches the
full build.
Add docs/tui2/performance-testing.md as a playbook for macOS sample
profiles and hotspot greps.
Expand transcript_view_cache tests to cover rebuild conditions, raster
equivalence vs direct rendering, user-row caching, and eviction.
Test: cargo test -p codex-tui2
Instead of querying all 256 terminal colors on startup, which was slow
in some terminals, hardcode the default xterm palette.
Additionally, tweak the shimmer so that it blends between default_fg and
default_bg, instead of "dark gray" (according to the terminal) and pure
white (regardless of terminal theme).
