Garbled/overlapping text in transcript during rapid bash execution with active subagents

Description

When multiple bash commands execute in quick succession while subagents are running and a custom status line is refreshing, the transcript renders garbled text — lines from different outputs overlap, partial commands appear interleaved, and some text renders on top of other text.

Steps to reproduce

1. Start a session with a custom statusLine configured in settings.json
2. Have Claude spawn a subagent (e.g., general-purpose agent running in background)
3. Run several bash commands in rapid succession (e.g., multiple rg calls, python3 -c commands)
4. Observe the transcript — output from different commands overlaps and renders garbled

Expected behavior

Each command's output renders cleanly in its own block in sequence.

Actual behavior

Text from different outputs overlaps, partial lines from one command appear within another's output block. See screenshot — the top portion shows interleaved bash output where command boundaries are unclear and text renders on top of other text.

Screenshot

<img width="895" height="1128" alt="Image" src="https://github.com/user-attachments/assets/40e4b5aa-1bc6-412d-a63a-26cbba5fc8a7" />

Environment

• macOS (also reproducible on Fedora 43)
• Default TUI mode (not fullscreen)
• Claude Opus 4.6 (1M context)
• Custom statusLine with 2-line output (padding: 2)
• Subagent active (general-purpose agent)

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This issue was created by Claude Opus 4.6 (1M context) via Claude Code.