fix: 终端内容溢出 viewport 时的重影 bug

主屏幕模式下 frame 持续溢出 viewport 时，cursor-restore LF 把内容滚入 scrollback
导致相对光标追踪漂移，可见区 diff 落到错误行产生重影（重复 banner / 错位）。
扩展 log-update overflow 分支为无条件 fullReset（含 \x1b[3J 清 scrollback），
并将主屏 self-healing 清屏从 ERASE_SCREEN (CSI 2 J) 换成 ERASE_DOWN (CSI J)，
避免 xterm.js / VSCode 集成终端的 scrollback 边界副作用。

Co-Authored-By: glm-5.2 <zai-org@claude-code-best.win>

packages/@ant/ink/src/core/ink.tsx

@@ -74,6 +74,7 @@ import {
   DISABLE_MODIFY_OTHER_KEYS,
   ENABLE_KITTY_KEYBOARD,
   ENABLE_MODIFY_OTHER_KEYS,
+  ERASE_DOWN,
   ERASE_SCREEN,
 } from './termio/csi.js';
 import {
@@ -106,6 +107,17 @@ const ERASE_THEN_HOME_PATCH = Object.freeze({
   type: 'stdout' as const,
   content: ERASE_SCREEN + CURSOR_HOME,
 });
+// Main-screen self-healing: CURSOR_HOME then ERASE_DOWN (CSI J) clears the
+// entire visible viewport from (0,0) without touching scrollback. ERASE_SCREEN
+// (CSI 2 J) on xterm.js / VSCode integrated terminals can produce residual
+// ghosting because its implementation interacts with the scrollback boundary;
+// CSI J has deterministic "erase from cursor to end of screen" semantics that
+// never push visible content into scrollback. Order matters: home first, then
+// erase — so the erase covers the full viewport.
+const HOME_THEN_ERASE_DOWN_PATCH = Object.freeze({
+  type: 'stdout' as const,
+  content: CURSOR_HOME + ERASE_DOWN,
+});
 
 // Cached per-Ink-instance, invalidated on resize. frame.cursor.y for
 // alt-screen is always terminalRows - 1 (renderer.ts).
@@ -783,10 +795,15 @@ export default class Ink {
     } else if (this.needsEraseBeforePaint && hasDiff) {
       // Main-screen periodic self-healing: clear visible terminal before
       // painting the diff. Without this, rows past the new frame's height
-      // would retain stale content from the previous frame. BSU/ESU keeps
-      // old content visible until the full erase+paint is flushed atomically.
+      // would retain stale content from the previous frame. Uses
+      // HOME_THEN_ERASE_DOWN_PATCH (CSI H + CSI J) instead of ERASE_SCREEN
+      // (CSI 2 J): the latter's behavior on xterm.js / VSCode integrated
+      // terminals can leave residual ghosting of the prior frame (banner +
+      // status bar duplicated). CSI J erases from cursor (now at 0,0) to
+      // end of screen with deterministic semantics and does not touch
+      // scrollback, so the user's conversation history is preserved.
       this.needsEraseBeforePaint = false;
-      optimized.unshift(ERASE_THEN_HOME_PATCH);
+      optimized.unshift(HOME_THEN_ERASE_DOWN_PATCH);
     }
 
     // Native cursor positioning: park the terminal cursor at the declared

packages/@ant/ink/src/core/log-update.ts

@@ -225,27 +225,23 @@ export class LogUpdate {
       cursorAtBottom &&
       !isGrowing
     ) {
-      // viewportY = rows in scrollback from content overflow
-      // +1 for the row pushed by cursor-restore scroll
-      const viewportY = prev.screen.height - prev.viewport.height
-      const scrollbackRows = viewportY + 1
-
-      let scrollbackChangeY = -1
-      diffEach(prev.screen, next.screen, (_x, y) => {
-        if (y < scrollbackRows) {
-          scrollbackChangeY = y
-          return true // early exit
-        }
-      })
-      if (scrollbackChangeY >= 0) {
-        const prevLine = readLine(prev.screen, scrollbackChangeY)
-        const nextLine = readLine(next.screen, scrollbackChangeY)
-        return fullResetSequence_CAUSES_FLICKER(next, 'offscreen', stylePool, {
-          triggerY: scrollbackChangeY,
-          prevLine,
-          nextLine,
-        })
-      }
+      // Frame persistently overflows the viewport. The cursor-restore LF at the
+      // end of the previous frame scrolled content into scrollback, and the
+      // terminal's auto-scroll on cursor movement causes our relative-cursor
+      // tracking to drift — visible-region diffs then land on the wrong rows
+      // and produce ghosting (duplicate banners, shifted content).
+      //
+      // Relative cursor ops can't repaint scrollback rows at all, and even
+      // visible-region writes are unsafe because the cursor origin we computed
+      // doesn't match where the terminal thinks it is. Full-reset emits
+      // clearTerminal (CSI 2 J + CSI 3 J + CSI H), wiping scrollback residue
+      // and cursor drift, then repaints the whole frame from (0,0).
+      //
+      // Previously this branch only fired when a diff existed in the scrollback
+      // region; visible-region-only changes still produced ghosting. Cost: an
+      // extra clear+repaint per render while content overflows. Acceptable
+      // because overflow is the exception, not the steady state of a TUI.
+      return fullResetSequence_CAUSES_FLICKER(next, 'offscreen', stylePool)
     }
 
     const screen = new VirtualScreen(prev.cursor, next.viewport.width)

packages/@ant/ink/src/core/termio/csi.ts

@@ -232,6 +232,12 @@ export const ERASE_SCREEN = csi(2, 'J')
 /** Erase scrollback buffer (CSI 3 J) */
 export const ERASE_SCROLLBACK = csi(3, 'J')
 
+/** Erase from cursor to end of screen (CSI J) — constant form.
+ *  Unlike ERASE_SCREEN (CSI 2 J), this never pushes content into scrollback
+ *  on xterm.js / VSCode integrated terminals, making it safe for periodic
+ *  self-healing redraws in main-screen mode. */
+export const ERASE_DOWN = csi('J')
+
 /**
  * Erase n lines starting from cursor line, moving cursor up
  * This erases each line and moves up, ending at column 1