statusLine: only first line renders when command outputs multiple lines

Bug description

When statusLine.command is configured to a script that prints multiple lines to stdout, only the first line renders in the terminal UI. Subsequent lines are silently dropped — not truncated/wrapped, just absent.

This contradicts the documented behavior: "each echo or print statement displays as a separate row."

Environment

• Claude Code version: 2.1.128
• OS: macOS 26.6.2 (BuildVersion 25G83)
• Terminal: Apple Terminal (TERM=xterm-256color)
• Backend: custom ANTHROPIC_BASE_URL pointing at an internal enterprise API proxy (not api.anthropic.com directly)
• statusLine config in settings.json:

``json
"statusLine": {
"type": "command",
"command": "~/.claude/statusline.sh",
"padding": 2,
"refreshInterval": 60
}
``

Steps to reproduce

1. Configure a statusLine command script that emits 2+ lines via separate printf/echo statements (e.g. line 1: model/dir info, line 2: a context-usage bar).
2. Start or resume a session.
3. Observe the terminal: only line 1 of the statusLine output appears below the prompt. Line 2+ never renders — not on first render, not after subsequent turns, and it's reproducible in a brand-new terminal window/session too (ruling out "hasn't refreshed yet" as an explanation).

Confirmation that the script itself is not at fault

I instrumented the script to capture its own full rendered output into a variable, print it, and also log a copy to a debug file on every real invocation during a live session. The debug log shows the script correctly emitting all 4 of its lines (env/model line, context-usage bar line, budget bar line, budget warning line) with correct live data on every invocation — while the terminal UI simultaneously displayed only line 1. This confirms the multi-line output reaches stdout correctly; the client is not rendering everything past the first line.

Expected behavior

All lines printed by the statusLine command should render, one per row, as documented.

Actual behavior

Only the first line renders; all subsequent lines are silently dropped from display.