REPL crash: terminal render overflow on large Edit output (860K chars)

Description

Claude Code crashes when the model generates a large Edit tool call response. The terminal render buffer overflows, causing the REPL to unmount immediately.

Steps to reproduce

1. Ask Claude Code to perform an edit that results in a large output
2. The model generates a response with a large Edit tool call
3. The REPL crashes

Debug log analysis

The terminal render goes from normal to catastrophic in a single frame:

# Normal frame just before crash:
[DEBUG] High write ratio: blit=0, write=23690 (100.0% writes), screen=228x79

# Crash frame — screen height jumps 57x, write volume jumps 36x:
[DEBUG] High write ratio: blit=0, write=860108 (100.0% writes), screen=12960x79
[DEBUG] [REPL:unmount] REPL unmounting

The screen went from 228 → 12,960 lines and write volume from 23K → 860K characters in a single render cycle. The REPL unmounts immediately after.

Timeline

1. A streaming stall of 55.4s occurred (Streaming stall detected: 55.4s gap between events)
2. After the stall, the response completed with an Edit tool call (permission prompt shown)
3. On the next render frame, the buffer exploded to 860K chars → crash

Expected behavior

The render engine should handle large outputs gracefully — truncate, paginate, or stream incrementally instead of writing 860K characters in a single frame.

Environment

• Claude Code version: 2.1.100
• OS: macOS (Darwin 25.3.0)
• Model: claude-opus-4-6 (1M context)