fix: textarea fallback 高度加入 offsetHeight - clientHeight 的边框差，溢出判断也改用完整 border-box 高度。

src/components/image-editor/EditorAgentConversation/EditorAgentDraftTextarea.test.tsx

@@ -18,12 +18,7 @@ describe('EditorAgentDraftTextarea', () => {
     vi.stubGlobal('CSS', { supports });
     vi.stubGlobal('ResizeObserver', resizeObserver);
 
-    render(
-      <EditorAgentDraftTextarea
-        value=""
-        onChange={onChange}
-      />,
-    );
+    render(<EditorAgentDraftTextarea value="" onChange={onChange} />);
 
     const input = screen.getByLabelText(
       '发送给画布 Agent',
@@ -65,6 +60,17 @@ describe('EditorAgentDraftTextarea', () => {
     ) as HTMLTextAreaElement;
     expect(observe).toHaveBeenCalledWith(input);
     let contentHeight = 92;
+    Object.defineProperty(input, 'offsetHeight', {
+      configurable: true,
+      get: () => {
+        const styleHeight = Number.parseFloat(input.style.height);
+        return Number.isNaN(styleHeight) ? 42 : styleHeight;
+      },
+    });
+    Object.defineProperty(input, 'clientHeight', {
+      configurable: true,
+      get: () => input.offsetHeight - 2,
+    });
     Object.defineProperty(input, 'scrollHeight', {
       configurable: true,
       get: () => contentHeight,
@@ -76,8 +82,9 @@ describe('EditorAgentDraftTextarea', () => {
         onChange={vi.fn()}
       />,
     );
-    expect(input.style.height).toBe('92px');
+    expect(input.style.height).toBe('94px');
     expect(input.style.overflowY).toBe('hidden');
+    expect(input.scrollHeight).toBeLessThanOrEqual(input.clientHeight);
 
     contentHeight = 180;
     act(() => {

src/components/image-editor/EditorAgentConversation/EditorAgentDraftTextarea.tsx

@@ -20,13 +20,18 @@ function supportsNativeFieldSizing() {
 function resizeFallbackTextarea(textarea: HTMLTextAreaElement) {
   textarea.style.height = 'auto';
   const contentHeight = textarea.scrollHeight;
+  const borderHeight = Math.max(
+    0,
+    textarea.offsetHeight - textarea.clientHeight,
+  );
+  const borderBoxContentHeight = contentHeight + borderHeight;
   const nextHeight = Math.min(
-    Math.max(contentHeight, DRAFT_MIN_HEIGHT_PX),
+    Math.max(borderBoxContentHeight, DRAFT_MIN_HEIGHT_PX),
     DRAFT_MAX_HEIGHT_PX,
   );
   textarea.style.height = `${nextHeight}px`;
   textarea.style.overflowY =
-    contentHeight > DRAFT_MAX_HEIGHT_PX ? 'auto' : 'hidden';
+    borderBoxContentHeight > DRAFT_MAX_HEIGHT_PX ? 'auto' : 'hidden';
 }
 
 export function EditorAgentDraftTextarea({