fix(tui): reduce scroll stutter by throttling UI refresh and caching renders

- Increased UI update interval from 350ms to 500ms
- Reduced dot animation frequency from 60ms to 250ms
- Reduced splash animation frequency from 50ms to 100ms
- Added content hash cache for rendered agent messages to avoid
  re-parsing markdown and re-running Pygments on every tick
- Added guard to prevent redundant scroll_end callbacks from queuing
  during rapid updates

Closes #581

strix/interface/tui/app.py

@@ -128,7 +128,7 @@ class SplashScreen(Static):  # type: ignore[misc]
         yield panel_static
 
     def on_mount(self) -> None:
-        self._animation_timer = self.set_interval(0.05, self._animate_start_line)
+        self._animation_timer = self.set_interval(0.1, self._animate_start_line)
 
     def on_unmount(self) -> None:
         if self._animation_timer is not None:
@@ -729,6 +729,7 @@ class StrixTUIApp(App):  # type: ignore[misc]
             "#86efac",  # Brightest
         ]
         self._dot_animation_timer: Any | None = None
+        self._pending_scroll_end = False
 
         self._setup_cleanup_handlers()
 
@@ -872,7 +873,7 @@ class StrixTUIApp(App):  # type: ignore[misc]
 
         self._start_scan_thread()
 
-        self.set_interval(0.35, self._update_ui)
+        self.set_interval(0.5, self._update_ui)
 
     def _update_ui(self) -> None:
         if self.show_splash:
@@ -1018,8 +1019,16 @@ class StrixTUIApp(App):  # type: ignore[misc]
         self._safe_widget_operation(chat_display.update, content)
         chat_display.set_classes(css_class)
 
-        if is_at_bottom:
+        if is_at_bottom and not self._pending_scroll_end:
-            self.call_later(chat_history.scroll_end, animate=False)
+            self._pending_scroll_end = True
+            self.call_later(self._do_scroll_end, chat_history)
+
+    def _do_scroll_end(self, chat_history: VerticalScroll) -> None:
+        self._pending_scroll_end = False
+        try:
+            chat_history.scroll_end(animate=False)
+        except Exception:
+            logger.debug("Failed to scroll chat to end", exc_info=True)
 
     def _get_chat_placeholder_content(
         self, message: str, placeholder_class: str
@@ -1292,7 +1301,7 @@ class StrixTUIApp(App):  # type: ignore[misc]
 
     def _start_dot_animation(self) -> None:
         if self._dot_animation_timer is None:
-            self._dot_animation_timer = self.set_interval(0.06, self._animate_dots)
+            self._dot_animation_timer = self.set_interval(0.25, self._animate_dots)
 
     def _stop_dot_animation(self) -> None:
         if self._dot_animation_timer is not None:

strix/interface/tui/renderers/agent_message_renderer.py

@@ -1,6 +1,6 @@
 import re
 from functools import cache
-from typing import Any
+from typing import Any, ClassVar
 
 from pygments.lexers import get_lexer_by_name, guess_lexer
 from pygments.styles import get_style_by_name
@@ -161,6 +161,8 @@ def _process_inline_formatting(line: str) -> Text:
 
 
 class AgentMessageRenderer:
+    _cache: ClassVar[dict[int, Text]] = {}
+
     @classmethod
     def render_simple(cls, content: str) -> Text:
         if not content:
@@ -168,4 +170,12 @@ class AgentMessageRenderer:
         cleaned = _BLANK_LINE_RUNS.sub("\n\n", content).strip()
         if not cleaned:
             return Text()
-        return _apply_markdown_styles(cleaned)
+        cache_key = hash(cleaned)
+        cached = cls._cache.get(cache_key)
+        if cached is not None:
+            return cached.copy()
+        rendered = _apply_markdown_styles(cleaned)
+        if len(cls._cache) > 100:
+            cls._cache.clear()
+        cls._cache[cache_key] = rendered
+        return rendered