A new internal env var preserves terminal dimensions across session relaunches. When Claude Code spawns a replacement process (upgrade self-respawn, background detach), it captures the current terminal size as COLUMNSxROWS and passes it forward so the new process renders at the correct width and height even when the TTY reports wrong dimensions.
Details
- Set automatically by Claude Code before relaunching; not intended for manual use
- Applies terminal size from the env var only when stdout is a TTY and the OS hasn't already reported a real size
- The env var is deleted from the process environment after being consumed
Evidence
Terminal size preservation (search for "CLAUDE_CODE_RELAUNCH_TERMINAL_SIZE")
Strings lifted out of the shipped bundle, so the claim above can be checked against them.