TUI: mouse-copying assistant output adds left padding and hard line-wraps, corrupting pasted text (grok cli / opencode are not affected)

Summary

When selecting assistant output (especially fenced code blocks) in the TUI with the mouse and copying it, the clipboard content is corrupted in two ways:

1. Every line carries the TUI's left padding (~4–5 leading spaces).
2. Long logical lines are hard-wrapped at the chat content width, so a single line is copied as multiple lines, with padding on the continuation lines.

grok cli and opencode render assistant content flush-left, so mouse-copying from them is lossless. In Kimi Code, the very common workflow of "copy a command the agent printed and paste it into a terminal" is actively dangerous.

Environment

• kimi 0.42.0
• Windows 11, PowerShell (oh-my-posh prompt)

Steps to reproduce

1. Ask the agent to print a multi-line shell snippet, or a single long command (e.g. echo '<a-long-string>' >> somefile).
2. Select the code block in the TUI with the mouse and copy it.
3. Paste into another terminal or an editor.

Expected behavior

The clipboard contains exactly the raw text the agent emitted — no added leading spaces, no inserted line breaks. This is how grok cli and opencode behave.

Actual behavior

• Each pasted line starts with the TUI's left-margin padding (visible as ~5 leading spaces).
• Lines longer than the chat content width arrive split at the visual wrap point; the continuation lines keep the padding, so a quoted string can be silently broken in the middle.

Real-world impact

While setting up SSH key authentication on a server, I copied a one-liner the agent printed:

echo 'ssh-ed25519 AAAA...<long-key>... user@host' >> ~/.ssh/authorized_keys

The paste arrived as two lines — the key body on one line and user@host (with leading spaces) on the next. authorized_keys ended up corrupted and sshd refused the key (Permission denied (publickey)). The break is invisible in a terminal, so it took an extra debugging round to find.

Related

• #2721 — fullscreen TUI with mouse selection/copy (broader UX request; this issue is specifically about copy fidelity of the normal transcript).

Start by tracing the TUI transcript rendering and mouse-selection clipboard path, reproducing the issue with a fenced snippet and a long command. The work is done when copied assistant output preserves its original leading spaces and logical line breaks, including long lines, and the reproduction no longer corrupts pasted shell commands.