fix(terminal): cap VirtualTerminal scrollback to bound memory and render cost - #387
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…der cost An append-only session grew the VirtualTerminal grid without limit; only the rendered copy was capped (slice(-maxLines)), so getLines() stayed an O(total-lines) scan on every terminal_output frame. Combined with retained background session screens this compounded the cumulative slowdown. Trim the oldest rows past a 10k cap and shift the cursor to match, so memory and per-frame cost stay bounded regardless of transcript length.
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Problem
VirtualTerminalgrew its internalgridwithout bound for an append-only session.Only the rendered copy was capped (
getLines().slice(-maxLines)), sogetLines()stayed an O(total-lines) scan run on everyterminal_outputframe, and memory grew with the full transcript.Combined with retained background session screens (see the stacked base PR) this compounded the cumulative slowdown after several sessions.
Fix
Trim the oldest rows once the grid passes a 10k cap and shift the cursor (
this.row) by the same amount so absolute row addressing stays correct.The cap sits well above any TUI screen height, so absolute cursor positioning never triggers the trim; only unbounded append-growth does.
Tests
Added a scrollback-cap case to
__tests__/unit/services/virtual-terminal.test.ts: an append-only stream past the cap stays bounded, keeps the newest line, and drops the oldest.Full VirtualTerminal suite green (220 tests).
Compatibility
Mobile-only, internal to the terminal emulator.
No server, API, or WS-contract changes.
Stacking
This PR is based on
perf/freeze-hidden-session-screens(#386), so its diff shows only the VirtualTerminal change.Merge #386 first, then this one, in integration-branch order.