fix(widgets): add max line limit and document multi-hook behavior

- Limit total widget lines to 10 to prevent viewport overflow/flicker
- Show '... (widget truncated)' when limit exceeded
- Document that multiple hooks stack widgets vertically
- Add caution about keeping widgets small

packages/coding-agent/docs/hooks.md

@@ -445,9 +445,10 @@ const currentText = ctx.ui.getEditorText();
 
 **Widget notes:**
 - Widgets are multi-line displays shown above the editor (below "Working..." indicator)
-- Multiple hooks can set widgets using unique keys
+- Multiple hooks can set widgets using unique keys (all widgets are displayed, stacked vertically)
 - Use for progress lists, todo tracking, or any multi-line status
 - Supports ANSI styling via `ctx.ui.theme` (including `strikethrough`)
+- **Caution:** Keep widgets small (a few lines). Large widgets from multiple hooks can cause viewport overflow and TUI flicker.
 
 **Styling with theme colors:**