The assistant bubble re-parsed rich Markdown on every stream_delta and rich-rendered it
twice per delta (once to paint, once to measure height) — O(N^2) over the answer length.
Fix the cost while keeping live markdown formatting:

- _ChatItemView.maybe_update now throttles assistant_message rebuilds to ~one per 150 ms
  (coalesced via set_timer). The ChatItem content still updates per delta; only the
  Markdown parse + rich render is deferred. Plain renderables (thinking/planning are
  Text) bypass the throttle — they are cheap. The first mutating delta rebuilds
  immediately for a snappy start; rapid bursts coalesce.
- get_content_height is cached by (renderable identity, width) so the layout pass no
  longer re-renders the rich renderable to measure it between throttled rebuilds.
- stream_end flushes any pending throttled rebuild so the final chunk of streamed text
  appears immediately instead of after the throttle window.
- A deferred rebuild re-anchors scroll to the bottom (via ChatPanel._stick_to_bottom)
  so the freshly rendered streaming text stays in view after its height grows.
- ThemedMarkdownRenderable.__rich_console__ now streams segments straight through
  instead of materializing them into a list first (no per-paint O(N) allocation +
  double walk); the link rewrite is inline in the loop.

Tests: adapted test_per_token_refresh_renders_only_the_streaming_item to the throttled
semantics (a burst yields a couple of rebuilds, not one per token, all for the assistant
item); added throttle-coalesces and stream_end-flushes tests. Full suite: 939 passed, 1 skipped.

All syntax-highlighted code in the TUI now resolves one Pygments style per
theme from a single point: Theme.code_theme (gnexus-dark=dracula,
gnexus-light=paraiso-light). Previously the dracula/github-light name was
duplicated in artifact.py and markdown_content.py, and the light theme's
"github-light" is not a real Pygments style (only github-dark exists), so
rich silently fell back to "default" and light-mode code was never
highlighted — fixed by switching to paraiso-light.

New renderers/syntax.py::highlight_code() is the shared Syntax factory
(always theme.code_theme + background_color=theme.surface.hex); artifact.py
and the new filesystem read path build through it, and
_theme_aware_code_theme now reads Theme.code_theme via ThemeRegistry.

filesystem FilesystemToolResultRenderer._render_read: the file body is now
syntax-highlighted via highlight_code with the language guessed from the
read path (guess_language). The server's "{num:>width}: {line}" prefix is
stripped (_strip_number_prefix) so Syntax renders its own line-number column
and multi-line constructs (triple-quoted strings, block comments) highlight
correctly across line boundaries; numbered=False renders without numbers.
The header plaque (accent path) and the large-file warning stay as Text;
body is Group(header, [warning,] Text, Syntax). Unknown extensions fall back
to the "text" lexer (plain).

Diff content keeps marker-only coloring (combining Pygments token styles
with the +/- tint is non-trivial); grep/list/info/find unchanged.

Tests: tests/clients/test_code_theme.py pins the single-point contract
(markdown/artifact/read all resolve theme.code_theme, dark != light);
test_filesystem_renderer read tests rewritten for the Group+Syntax body,
plus language-guess and numbered=False coverage. Full suite: 932 passed.

Long assistant messages vanished past the chat panel's right edge instead
of wrapping: ThemedMarkdownRenderable built its rich Console at
console.width, which is the physical terminal width (e.g. 80), but the
markdown lives in a narrower Panel. options.max_width holds the real
available columns (panel inner width minus borders/padding); rich wrapped
to the terminal width while the visible area was narrower, so the right
side of every long line was cut off. Use options.max_width, falling back to
console.width only when it is unset.

- Add CommandPaletteScreen modal with fuzzy filtering and keyboard navigation.

- Bind Ctrl+P to push the palette; selected commands execute via registry.

- Make MarkdownRenderer theme-aware: headings, inline code, links, and code blocks use gnexus palette.

- Pick dracula/github-light code theme based on active theme brightness.

Co-Authored-By: Claude <noreply@anthropic.com>

- Add clients/terminal/tui package with micro-architecture:
  - events, context, chat_model, ws_bridge, permissions engine.
  - widgets: ChatPanel, StatusPanel, InputBox.
  - renderers: user/assistant messages, thinking, tool calls, errors,
    markdown, plain — registry-based and extensible.
  - slash commands: /help, /new, /sessions, /switch, /profile, /thinking,
    /compact, /quit — registry-based and extensible.
- Wire navi-code to launch TUI by default; keep click-CLI via --raw.
- Add textual>=0.70 dependency.
- Add TUI smoke tests via Textual Pilot.
- Add docs/plan_navi_code_tui.md with full Phase 4/5 roadmap.

Tests: 463 passed, 1 skipped (excluded unrelated websocket test).

Co-Authored-By: Claude <noreply@anthropic.com>