Windows Terminal rendering broken after /statusline - scroll margins not reset

Bug Report: Windows Terminal Rendering Issues After /statusline

Environment

• OS: Windows 11 (MSYS_NT-10.0-26200)
• Terminal: Windows Terminal / PowerShell
• Claude Code Version: v2.0.73
• Model: Opus 4.5

Summary

After running /statusline command, terminal rendering is broken in PowerShell/Windows Terminal. Content is missing, truncated, or overwritten. The issue does NOT occur in CMD.

Symptoms

Symptom 1: Last line of output hidden

• When displaying 10 lines of text, line 10 is not visible
• Works correctly in CMD
• Caused by DECSTBM scroll margins not being reset

Symptom 2: Content in middle of output missing

• Insight sections partially rendered
• Lines appear truncated on the left side
• Content appears fragmented (e.g., "before the next batch." floating without context)

Symptom 3: Lines 1-9 hidden, only line 10 visible

• Asked for 10-line output
• Only the last line rendered
• Previous lines completely missing

Root Cause Analysis

1. Scroll Margins (DECSTBM): The /statusline feature uses ESC[<top>;<bottom>r to reserve the bottom line. These margins are NOT properly reset when statusline fails or is disabled on Windows Terminal.

1. Cursor Manipulation: Claude Code uses ANSI escape codes (\033[F move up, \033[K clear line) that overwrite previous content on Windows.

1. ConPTY Differences: Windows Terminal uses ConPTY which maintains ANSI state (including scroll margins), while CMD's legacy console often resets them.

Reproduction Steps

1. Start Claude Code in Windows Terminal (PowerShell)
2. Run /statusline
3. Exit or disable statusline
4. Ask Claude to output 10 lines of text
5. Observe: last line (or multiple lines) are hidden

Partial Workaround Found

Resetting scroll margins with:

[Console]::Write([char]27 + "[r")

This fixes the "last line hidden" symptom but does NOT fix the content overwriting/truncation issues.

Related Issues

• #4897 - Console output overwritten on Windows (CRITICAL)
• #8618 - CLI Terminal UI Rendering Corrupted (SHOW-STOPPER)
• #14125 - StatusLine not rendering in Windows Terminal
• #6526 - StatusLine not displaying on Windows 11

Expected Behavior

• All output lines should be visible
• Content should not be truncated or overwritten
• /statusline should properly clean up terminal state when disabled

Suggested Fix

1. Reset scroll margins (ESC[r) when statusline is disabled
2. Consider disabling cursor manipulation ANSI codes on Windows
3. Test terminal state cleanup on Windows Terminal specifically