fix: 修复消息区溢出布局问题，恢复Spacer弹性空白

- 消息区添加 .height(maxMessageLines) + .overflow(HIDDEN) 防止溢出
- 恢复 Spacer.create() 在消息少时填充空白
- AskUser工具添加调试日志帮助排查结构化回调

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/main/java/com/claudecode/tool/impl/AskUserQuestionTool.java

@@ -86,6 +86,7 @@ public class AskUserQuestionTool implements Tool {
 
         // 优先使用结构化回调（支持交互式选择）
         Object structuredCb = context.get(ASK_USER_STRUCTURED_CALLBACK);
+        log.debug("Structured callback type: {}", structuredCb != null ? structuredCb.getClass().getName() : "null");
         if (structuredCb instanceof java.util.function.BiFunction<?, ?, ?> biFn) {
             try {
                 var askFn = (java.util.function.BiFunction<String, java.util.List<String>, String>) biFn;
@@ -97,6 +98,9 @@ public class AskUserQuestionTool implements Tool {
             } catch (Exception e) {
                 log.debug("Structured callback failed, falling back", e);
             }
+        } else {
+            log.debug("Structured callback not a BiFunction, got: {}",
+                    structuredCb != null ? structuredCb.getClass().getInterfaces()[0] : "null");
         }
 
         // 回退到简单文本回调

src/main/java/com/claudecode/tui/ClaudeCodeComponent.java

@@ -265,7 +265,9 @@ public class ClaudeCodeComponent extends Component<ClaudeCodeComponent.TuiState>
         return Box.of(visibleItems.toArray(new Renderable[0]))
                 .flexDirection(FlexDirection.COLUMN)
                 .paddingTop(1)
-                .paddingX(1);
+                .paddingX(1)
+                .height(Math.max(1, maxLines))
+                .overflow(io.mybatis.jink.style.Overflow.HIDDEN);
     }
 
     /** 将 UIMessage 渲染为 Renderable 列表（一条消息可能产生多行） */