Scrollback duplication: TUI redraw without alternate screen causes doubled lines

Description

Claude Code v2.1.215 streams text output into the main screen buffer, then performs a full-screen TUI redraw from cursor home (CUP 1;1) — without ever entering alternate screen mode (DECSET 1049h). This causes lines to appear twice when scrolling back: once from the original streaming output (in scrollback) and once from the TUI redraw (on screen).

Reproduction

1. Launch claude --name "test" inside a terminal that records raw output (or use a ConPTY-based terminal emulator)
2. Run a command that produces multi-screen output (e.g. a review or analysis task)
3. When Claude finishes and redraws the TUI, scroll up
4. Lines near the top of the visible screen appear duplicated — they exist both in scrollback (from streaming) and on screen (from the TUI redraw)

Raw data analysis

Captured via .rtrec session recording in a ConPTY-based terminal emulator:

• No DECSET 1049h (alternate screen) anywhere in the entire session — confirmed by searching all output records
• At completion, Claude sends a large record streaming the full output via CR LF (content scrolls into scrollback normally)
• Immediately followed by two consecutive cursor-home redraws (CUP 1;1 + full screen content), slightly different from each other (off by one row), in the same main buffer
• The last line of a wrapped paragraph ends up in scrollback from the streaming output AND at the top of the visible screen from the redraw

Expected behavior

Claude Code should either:

• Enter alternate screen mode (DECSET 1049h / DECSET 1047h) for TUI rendering so redraws don't pollute scrollback, or
• Avoid re-sending content that's already in the scrollback when doing cursor-home redraws

Environment

• Claude Code v2.1.215
• Windows 11 (ConPTY)
• Terminal: custom ConPTY-based emulator (but the issue is in the escape sequences Claude sends, not in terminal handling)