fix(cli): only exit alternate screen buffer on SIGINT if it was entered

[jrvb-rl]

Summary

• The global SIGINT handler in cli.ts unconditionally sent \x1b[?1049l (exit alternate screen buffer) on every Ctrl+C, even when no TUI was active.
• Terminals interpret that sequence by restoring their last saved cursor position — jumping the cursor to the top of the screen and leaving all plain-text output (e.g. the rli d ssh provisioning wait loop) rendered below the restored cursor.
• Fix: track whether enterAlternateScreenBuffer() was actually called in a boolean in screen.ts, and guard the SIGINT handler so it only exits the buffer when needed.

Root cause

rli d ssh dbx_<id> goes through the plain Commander path — it never calls enterAlternateScreenBuffer(). Pressing Ctrl+C while waiting for a provisioning devbox fired the SIGINT handler which always wrote \x1b[?1049l. If the terminal had a stale saved-cursor position from a prior TUI session, that escape sequence restored it, jumping the cursor and garbling the output.

Test plan

• rli d ssh <id> against a provisioning devbox: confirm Ctrl+C exits cleanly with the cursor at the bottom of the output, no jumping.
• rli (interactive TUI): confirm Ctrl+C still exits the alternate screen buffer and restores the normal terminal view.
• rli d pty <id>: same check as TUI.

🤖 Generated with Claude Code

[sid-rl]

maybe worth adding a small test to verify isInAlternateScreenBuffer() starts as false, is true after enterAlternateScreenBuffer(), and false after exitAlternateScreenBuffer()

[jrvb-rl]

Added tests/__tests__/utils/screen.test.ts covering false → true → false around enter/exit. (ac87f8b)

[sid-rl]

we should also move, or document a follow-up to move, benchmark-job watch to use these helpers (right now it does its own handling of the raw escape sequences, but that also means isInAlternateScreenBuffer() is false when we're in the benchmark-job watch alternate screen buffer -- potential footgun)

[jrvb-rl]

Migrated benchmark-job watch to the shared helpers (replaced its raw enterAltScreen/exitAltScreen/cursor/clear sequences). isInAlternateScreenBuffer() now reports true while in the watch alt-screen, so the global SIGINT handler restores it correctly. (ac87f8b)