perf: Cache rendered message rows to avoid redundant processing.

mainline.py

@@ -826,6 +826,7 @@ def stream(items):
     MSG_COLOR = "\033[1;38;5;87m"    # sky cyan
     MSG_META  = "\033[38;5;245m"     # cool grey
     MSG_BORDER = "\033[2;38;5;37m"   # dim teal
+    _msg_cache = (None, None)        # (cache_key, rendered_rows)
 
     while queued < HEADLINE_LIMIT or active:
         t0 = time.monotonic()
@@ -846,11 +847,16 @@ def stream(items):
         if msg_active:
             # ── MESSAGE state: freeze scroll, render message ──
             buf = []
-            # Render message text with OTF font
+            # Render message text with OTF font (cached across frames)
             display_text = m_body or m_title or "(empty)"
             display_text = re.sub(r"\s+", " ", display_text.upper())
-            msg_rows = _big_wrap(display_text, w - 4)
-            msg_rows = _lr_gradient(msg_rows)
+            cache_key = (display_text, w)
+            if _msg_cache[0] != cache_key:
+                msg_rows = _big_wrap(display_text, w - 4)
+                msg_rows = _lr_gradient(msg_rows)
+                _msg_cache = (cache_key, msg_rows)
+            else:
+                msg_rows = _msg_cache[1]
             # Center vertically in scroll zone
             total_h = len(msg_rows) + 4  # +4 for border + meta + padding
             y_off = max(0, (sh - total_h) // 2)