diff --git a/packages/cli/src/ui/components/BaseTextInput.test.tsx b/packages/cli/src/ui/components/BaseTextInput.test.tsx
index 8dd908016e6..79da6876fec 100644
--- a/packages/cli/src/ui/components/BaseTextInput.test.tsx
+++ b/packages/cli/src/ui/components/BaseTextInput.test.tsx
@@ -7,6 +7,7 @@
 import { describe, it, expect, vi, beforeEach } from 'vitest';
 import { render } from 'ink-testing-library';
 import type { DOMElement } from 'ink';
+import stringWidth from 'string-width';
 import {
   BaseTextInput,
   defaultRenderLine,
@@ -183,6 +184,49 @@ describe('BaseTextInput', () => {
       }),
     ).toEqual({ x: 29, y: 20 });
   });
+
+  it.each([
+    { columns: 11, label: 'session', expectedLabel: 'sessi…' },
+    { columns: 12, label: '会话标题', expectedLabel: '会话标…' },
+    { columns: 20, label: 'session', expectedLabel: 'session' },
+    { columns: 4, label: 'session', expectedLabel: '' },
+  ])(
+    'keeps the top border within $columns columns for "$label"',
+    ({ columns, label, expectedLabel }) => {
+      const originalDescriptor = Object.getOwnPropertyDescriptor(
+        process.stdout,
+        'columns',
+      );
+      Object.defineProperty(process.stdout, 'columns', {
+        configurable: true,
+        value: columns,
+      });
+
+      try {
+        const { lastFrame } = render(
+          <BaseTextInput
+            buffer={createBuffer()}
+            onSubmit={vi.fn()}
+            topRightLabel={label}
+          />,
+        );
+        const topBorderLine = lastFrame()?.split('\n')[0] ?? '';
+
+        expect(stringWidth(topBorderLine)).toBe(columns);
+        if (expectedLabel) {
+          expect(topBorderLine).toContain(` ${expectedLabel} `);
+        } else {
+          expect(topBorderLine).toBe('─'.repeat(columns));
+        }
+      } finally {
+        if (originalDescriptor) {
+          Object.defineProperty(process.stdout, 'columns', originalDescriptor);
+        } else {
+          Reflect.deleteProperty(process.stdout, 'columns');
+        }
+      }
+    },
+  );
 });
 
 describe('getAbsolutePosition', () => {
diff --git a/packages/cli/src/ui/components/BaseTextInput.tsx b/packages/cli/src/ui/components/BaseTextInput.tsx
index 5587ecf6f18..b72c978085e 100644
--- a/packages/cli/src/ui/components/BaseTextInput.tsx
+++ b/packages/cli/src/ui/components/BaseTextInput.tsx
@@ -28,10 +28,13 @@ import type { Key } from '../hooks/useKeypress.js';
 import { useKeypress } from '../hooks/useKeypress.js';
 import { keyMatchers, Command } from '../keyMatchers.js';
 import stringWidth from 'string-width';
-import { cpSlice, cpLen } from '../utils/textUtils.js';
+import { cpSlice, cpLen, truncateToWidth } from '../utils/textUtils.js';
 import { theme } from '../semantic-colors.js';
 import { renderSoftwareCursor } from '../utils/software-cursor.js';
 
+const TOP_BORDER_LABEL_DECORATION_WIDTH = 4;
+const TOP_BORDER_MIN_LEADING_DASHES = 1;
+
 // ─── Types ──────────────────────────────────────────────────
 
 export interface RenderLineOptions {
@@ -340,11 +343,18 @@ export const BaseTextInput = ({
 
   const columns = process.stdout.columns || 80;
   // Build the top border line: ─────── label ──
-  // Label takes: 1 space + text + 1 space + 2 trailing dashes = label.length + 4
-  const labelWidth = topRightLabel ? stringWidth(topRightLabel) + 4 : 0;
-  const dashCount = Math.max(1, columns - labelWidth);
-  const topBorderLine = topRightLabel
-    ? `${'─'.repeat(dashCount)} ${topRightLabel} ${'─'.repeat(2)}`
+  // Reserve the label decoration and at least one leading dash.
+  const labelBudget =
+    columns - TOP_BORDER_LABEL_DECORATION_WIDTH - TOP_BORDER_MIN_LEADING_DASHES;
+  const renderedLabel = topRightLabel
+    ? truncateToWidth(topRightLabel, labelBudget)
+    : '';
+  const labelWidth = renderedLabel
+    ? stringWidth(renderedLabel) + TOP_BORDER_LABEL_DECORATION_WIDTH
+    : 0;
+  const dashCount = columns - labelWidth;
+  const topBorderLine = renderedLabel
+    ? `${'─'.repeat(dashCount)} ${renderedLabel} ${'─'.repeat(2)}`
     : '─'.repeat(columns);
 
   return (