Fix input lag on long-running sessions: bound live emulator scrollback - #923
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…measured data Two warnings from /review on the live-scrollback-cap fix (#923): - Missing a gotchas/pty-terminal.md entry per this repo's own documentation rule for non-obvious invariants/fixes. Added, including the residual-cost caveat (this mitigates rather than eliminates the O(n) eviction) and the known resize-taller backfill trade-off the reviewer identified. - The 1,000-line cap wasn't grounded in measured data the way the sibling replayScrollbackSize constant is. Benchmarked a synthetic 500-line burst feed at the old 10K cap vs the new 1K cap (~7.9ms vs ~5.0ms on an Apple M5 Max) and folded the real numbers into the code comment. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>
…g sessions x/vt's Scrollback.Push evicts the oldest line via slices.Delete(s.lines, 0, 1) once at capacity — an O(cap) shift of the whole backing slice, paid on every line that scrolls off the top of the screen. The live agent-view emulator never overrode x/vt's 10K-line default, so any long-running, high-output session pays that shift on every subsequent scrolled line, synchronously on the tview main goroutine inside SafeEmuWrite — the same goroutine that processes keyboard input. Confirmed against a real 18+ hour, 2MB+ log task. Cap the live emulator's scrollback 10x smaller (1K lines), mirroring the existing pattern for the replay emulator's cap. Deep scroll-back-in-history already goes through the separate 50K-line replay emulator built for scroll mode, so this has no user-visible effect on how far back a user can scroll. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>
…measured data Two warnings from /review on the live-scrollback-cap fix (#923): - Missing a gotchas/pty-terminal.md entry per this repo's own documentation rule for non-obvious invariants/fixes. Added, including the residual-cost caveat (this mitigates rather than eliminates the O(n) eviction) and the known resize-taller backfill trade-off the reviewer identified. - The 1,000-line cap wasn't grounded in measured data the way the sibling replayScrollbackSize constant is. Benchmarked a synthetic 500-line burst feed at the old 10K cap vs the new 1K cap (~7.9ms vs ~5.0ms on an Apple M5 Max) and folded the real numbers into the code comment. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>
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x/vt's Scrollback.Push evicts the oldest line via slices.Delete(s.lines, 0, 1) once at capacity — an O(cap) shift of the whole backing slice, paid on every line that scrolls off the top of the screen. The live agent-view emulator never overrode x/vt's 10K-line default, so a long-running, high-output session pays that shift on every subsequent scrolled line, synchronously on the tview main goroutine — the same goroutine that processes keyboard input. Confirmed against a real 18+ hour, 2MB+ log task.
Caps the live emulator's scrollback 10x smaller (1K lines), mirroring the existing pattern for the replay emulator's cap. Deep scroll-back-in-history already goes through the separate 50K-line replay emulator built for scroll mode, so this has no material effect on how far back a user can scroll. Grounded the cap in a measured benchmark and documented the fix + its residual-cost/edge-case trade-offs in gotchas/pty-terminal.md per review feedback.
Co-Authored-By: Claude noreply@anthropic.com