Four fixes for the scrollback reports in #205 (plus its follow-up comment).
1. tmux-backed shell/opencode/antigravity sessions were parked in xterm's
ALTERNATE buffer for their whole life. The tmux CLIENT emits smcup
(\x1b[?1049h) as its first bytes on attach, and the existing strip is gated
to claude/codex/gemini, so it reached the browser verbatim. In the alternate
buffer baseY is pinned at 0 (no scrollback, so touch scrolling is a no-op)
and xterm's own wheel handler translates the wheel into \x1bOA cursor keys,
which readline receives as shell history navigation. Both reported symptoms,
one sequence. isMuxAltScreenOnlyStripMode() now strips that toggle for those
modes, but ONLY under tmux (the direct-PTY fallback still needs a program's
own alt screen) and ONLY the alt-screen toggle: 3J from a user's `clear` and
the mouse DECSETs a pane's htop/vim rely on are left alone. Safe because tmux
never forwards a pane's alt-screen toggles to its client, it repaints;
captured from a real attach, vim/less/htop emit zero.
2. "Load more history" on scroll-to-top. xterm's buffer is only ever a window
onto tmux's history, and tmux repaints the pane rectangle instead of emitting
linefeeds whenever output outpaces its flush, OVERWRITING already-rendered
scrollback. Measured: a 60-line burst added 1 row and destroyed 34, while the
same 60 lines emitted slowly added all 60. Scrolling up at the top now
re-pulls the full tmux scrollback and holds the user's place. Verified
end to end: 42 rendered rows -> 213, recovering all 150+60 printed lines.
3. The full-scrollback replay was gated on a single "first load after page load"
flag, which whichever session auto-selected consumed, so every other tab
started with one visible frame. Now tracked per session.
4. _wheelScrollLines ignored ev.deltaMode, so Firefox (DOM_DELTA_LINE, deltaY 3
per notch) scrolled one line where Chrome scrolls four or five, and capped
the forwarded SGR report at one tick. Line and page deltas are now converted,
and a pure horizontal swipe no longer falls through to a phantom -1.
Analysis and measurements: docs/scrollback-issues-analysis.md
Terminal scroll-up intermittently broke for Claude sessions (most visible on
iPhone). Claude Code periodically emits alt-screen switches (?1049h/?47h/?1047h),
scrollback-erase (3J), and mouse-tracking enables for full-screen UIs, which move
xterm.js to the scrollback-less alt buffer / wipe saved lines / hijack the wheel.
Codeman stripped these but only for codex mode.
Share the strip via isAltScreenStripMode(mode) = codex || claude, applied at both
sites that were codex-only: the live PTY stream (Session._handleTerminalOutput,
incl. the chunk-boundary carry) and the /terminal buffer replay. shell stays
excluded (vim/less/htop need the alt screen); opencode unchanged.
Tests: test/claude-scrollback-strip.test.ts (8 new); codex strip tests unchanged.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Codeman maintainer