Statusline/layout oscillates ±1 line while a background task runs (blank status row toggling) — regression in 2.1.186

Found 3 possible duplicate issues:

1. https://github.com/anthropics/claude-code/issues/20427
2. https://github.com/anthropics/claude-code/issues/69817
3. https://github.com/anthropics/claude-code/issues/43391

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Not a duplicate of the three suggested — checked each:

• #20427 — viewport jitter from auto-scroll/anchoring during active generation (filed Jan 2026, closed). Different cause; this report is about an idle, blank status row toggling, and is specific to 2.1.186.
• #43391 — duplicated/overlapping task panes and status rows (render-on-top corruption), already closed as a duplicate. Different symptom from a single blank row toggling ±1 line.
• #69817 — closest, and likely the same root cause (a status row whose show/hide changes terminal height → the whole view flickers). But the trigger and surface differ: #69817 is the VS Code extension's ⧉ In <file> context line under the VS Code integration. This issue has no VS Code involved — it's a background-task status row in plain Apple Terminal, and it's a clean 2.1.185 → 2.1.186 regression (onset matched the auto-update exactly; 2.1.186 changed background-task display and also shipped statusline regression #70421).

Requesting this stay open. If maintainers confirm #69817 and this share one underlying "status-row height toggling" fix, happy to consolidate — but the background-task trigger (no VS Code) and the precise 2.1.186 regression window are distinct, repro-backed data points worth keeping.

Still reproduces on 2.1.201 (current latest as of this writing), macOS, native installer.

Two data points to add:

1. The 2.1.198 change making subagents run in the background by default has widened the blast radius. Since any actively-working session now almost always has a background task alive, the ±1-line oscillation runs for essentially the entire duration of normal work (the whole time the spinner is going), not just during explicit run_in_background commands. With several parallel worker sessions on screen, all of them twitch continuously.

1. Not specific to Apple Terminal. Also reproduces with Claude Code running inside Emacs terminal emulators (TERM=xterm-256color). The symptom matches OP's diagnosis exactly: a blank/zero-content status row toggling in and out directly below the permission-mode footer line (">> bypass permissions on"), shifting everything above it up/down by one line.

No custom statusLine configured, so the statusline-script trailing-newline cause is ruled out.

Thanks for the detailed report. I tried hard to reproduce this on Linux on the current release 2.1.233 — and also on 2.1.186, the version you identified as the first bad one — and couldn't get the oscillation in either:

• Started a background task both ways: a sleep run in the background by Claude (run_in_background: true) and a ! bash-mode command backgrounded with ctrl+b
• Left the session idle with the task running, in both the default and fullscreen (/tui) renderers, at 100×30 and 80×24
• Captured the screen every 0.5s for 15–20s and diffed: every snapshot was byte-identical — no ±1-line movement

Since 2.1.186 itself doesn't show it in this setup, it looks environment-specific rather than fixed-in-the-meantime. To pin it down, could you share:

1. Does it still happen for you on the current release (2.1.233+)?
2. Do you have a custom status line configured (a statusLine command in ~/.claude/settings.json)? If so, does removing it temporarily stop the oscillation?
3. Your terminal window size, and the output of /status
4. If possible, a short screen recording of the oscillation

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We weren't able to reproduce this. Could you provide steps to trigger the issue — what you ran, what happened, and what you expected? This issue will be closed automatically if there's no activity within 7 days.