feat(stlxterm): VT100/xterm escape expansion

[FlareCoding]

Summary

• stlxterm parsed six CSI sequences, far short of the xterm dialect that TERM=xterm now promises, so full-screen apps rendered garbage.
• Adopts the escape coverage proven in the closed Vim port (Port Vim to Stellux: kernel termios/ioctl, stlxterm VT100, and Vim cross-compilation #113): scroll regions, insert/delete line and character, all erase variants, cursor save/restore/hide, alternate screen, plus PgUp/PgDn/Insert and F1-F12 keys.
• Improves on Port Vim to Stellux: kernel termios/ioctl, stlxterm VT100, and Vim cross-compilation #113 by actually rendering reverse video, matching xterm for reverse-index outside the scroll region, and guarding 1049 alt-screen transitions against stray or nested switches. The terminal also reports its real grid via TIOCSWINSZ.

Supersedes #142, which became unmergeable after GitHub flagged it as a stack.

Made with Cursor

[cursor]

Current version of PR was reviewed by /review-bugbot on Jul 30, 13:23 PDT. It flagged 2 findings.

Show 2 findings

1. DECSTBM homes wrong cursor row

userland/apps/stlxterm/src/term.c:400 · Medium Severity

After handling DECSTBM (CSI r), the cursor is always placed at screen row 0 instead of the top line of the newly configured scroll region (scroll_top). Programs that set a non-zero top margin (e.g. \e[2;24r) expect the cursor at that margin line; placing it at row 0 breaks origin/region-relative drawing and scrolling.

2. Alt screen keeps scroll margins

userland/apps/stlxterm/src/term.c:157 · Medium Severity

Switching to or from the alternate screen (DECSET 1047/1049) saves and restores cell buffers and cursor position but never resets or restores scroll_top/scroll_bottom. xterm-compatible full-screen apps expect full-window margins on the alt buffer and the previous margins restored on exit.

^{Bugbot on commit 3fe29bb is skipped.}