[Bug] Scroll position resets to top during agent execution

[rockyway]

Bug Description
when the agent is working, I scroll to view the previous content, then the scroll view is reset to top position, expect to maintain at where I am scrolling.

Environment Info

• Platform: darwin
• Terminal: iTerm.app
• Version: 2.1.76
• Feedback ID: af9d0228-569e-4113-9533-a89e8deeb1a0

Note: Content was truncated.

[VoxCore84]

We hit this too and collected working workarounds into a repo: claude-code-scroll-fix

Quick fix (Windows Terminal): Add "snapOnOutput": false to your profiles.defaults in settings.json. Reduces jumping ~60-70%.

Complete fix: Run Claude inside tmux — it completely decouples your scroll position from Claude's cursor repositioning. The repo has a one-click installer that sets up WSL + tmux + a Windows Terminal profile.

Root cause: Claude Code uses CSI escape sequences to rewrite the thinking spinner in-place, and terminals follow the cursor position back up. snapOnOutput only fixes output-triggered scrolling, not cursor repositioning — tmux fixes both.

[cruzlauroiii]

Confirmed same behavior on Windows Terminal + PowerShell (v2.1.76). Filed #34794 with Windows-specific details. This affects multiple platforms (macOS iTerm, Windows Terminal, WSL2) — likely a core rendering/cursor issue in the CLI output layer.

[cruzlauroiii]

Root cause traced in cli.js v2.1.76 source: Ink's rendering uses \ on every re-render. When output is large, the cursor moves far up in the buffer and Windows Terminal (and iTerm) follows the cursor, snapping the viewport to the top. Full analysis in #34794.

[cruzlauroiii]

Updated PR #34798 with v2 fix: stateful stdout.write interceptor that clamps cursor-up across ALL writes (not just sync blocks). Catches Ink renderer, prompt renderer, and all other cursor-up sources. Patch + PowerShell script included.

[cruzlauroiii]

Updated PR #34798 with 3 combined patches: (1) stateful stdout.write interceptor clamping cursor-up, (2) render throttle 16ms→200ms, (3) disable synchronized update mode. All three are needed — cursor-up clamping alone does not fix it because Windows Terminal exits scroll mode on ANY stdout write, and sync blocks batch writes into one viewport-resetting update. PowerShell apply/revert script included.

[cruzlauroiii]

v3 update: Previous fixes (cursor-up clamping, disabling sync update) did not work and caused flickering.

Root cause identified: Windows Terminal bug microsoft/terminal#14774 — SetConsoleCursorPosition always scrolls viewport to cursor, even when visible. Every Ink re-render triggers this. Cannot be fixed from within the process.

v3 patch: render throttle SK6=16 → SK6=1000 (1fps). Gives 1 second of uninterrupted reading between viewport resets. Trade-off: streaming text in ~1s chunks. No flickering.

PR #34798 updated. Real fix needs Microsoft (terminal#14774) or Anthropic (PTY proxy/append-only rendering).

[cruzlauroiii]

v5 update: Fundamentally different approach — buffer ALL Ink renders during active work, screen stays frozen (no viewport jumping). Flush only when (a) user types (at prompt/bottom, safe to update) or (b) 5s of no renders (Claude finished). Previous v1-v4 failed because WT bug microsoft/terminal#14774 triggers viewport scroll on ANY cursor positioning. v5 avoids this by not writing to stdout at all during active work. Trade-off: no spinner/progress visible during work. PR #34798 updated.