Replace the spacer-estimate scrollback model with an explicit history
row buffer owned by TerminalCore, rendered with absolute-positioned
virtual scrolling so huge outputs (cat of 50k-line files) stay smooth.
core.rs:
- TerminalCore owns history_rows + a cached screen, captured after each
process() via a bounded "conveyor belt" read of vt100 scrollback
- feed bytes in newline-bounded safe slices so a capture never reads
deeper than viewport_rows (works around vt100 0.15 visible_rows
subtract-overflow panic)
- handle clear (ESC[3J) by wiping our own history buffer
- TerminalSegment carries grid column count for exact-width rendering
- collect_window() clones only the visible slice
component.rs:
- TerminalCore lives in an RwSignal; render driven by an rAF-coalesced
render_tick so packet bursts collapse into one frame
- virtual_window pins to the bottom in live mode, follows scroll_top in
history mode; absolute-positioned rows in a fixed-height sizer keep
scroll geometry constant (fixes the "keeps drifting up" bounce)
- position-based programmatic-scroll detection replaces the racy
ignore-next-scroll flag
- alt-screen wheel events translate to arrow keys (vim/less paging)
- try_* signal access guards against disposal during hydration
style: lock row height to 18px, segment width to Nch (exact grid so
fallback-font glyphs like btm braille can't push the row sideways),
absolute-position the virtual rows layer.
Adds 12 unit tests (capture, clear, alt-screen, window slicing, wheel
mapping) and TERMINAL_ROADMAP.md tracking xterm.js parity work.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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