fix(string): strip newlines in shorten_middle before the length check

[Ricardo-M-L]

Problem

shorten_middle(text, width, remove_newline=True) is used by extract_key_argument to render a single-line summary of a tool call's key argument:

key_argument = shorten_middle(key_argument, width=50)

But the function returns early on short input before collapsing newlines:

def shorten_middle(text, width, remove_newline=True):
    if len(text) <= width:
        return text                       # <-- newlines never stripped here
    if remove_newline:
        text = _NEWLINE_RE.sub(" ", text)
    return text[: width // 2] + "..." + text[-width // 2 :]

So any key argument shorter than width that contains a newline — a multi-line Bash command, a Grep pattern, a multi-line SearchWeb query — is returned with its newlines intact, and the tool status line wraps across multiple lines instead of staying on one.

Reproduction (current behavior on main):

>>> shorten_middle("ls -la\npwd\necho done", 50)   # 20 chars, well under width
'ls -la\npwd\necho done'   # newlines leak into the single-line summary

Fix

Collapse newlines first, then do the length check and middle-truncation:

def shorten_middle(text, width, remove_newline=True):
    if remove_newline:
        text = _NEWLINE_RE.sub(" ", text)
    if len(text) <= width:
        return text
    return text[: width // 2] + "..." + text[-width // 2 :]

The length check now also operates on the post-flattening length, which is what actually gets displayed. Behavior with remove_newline=False is unchanged.

Tests

shorten_middle had no tests; added coverage to tests/utils/test_shorten.py:

• short text passthrough,
• newline stripping in short text (the bug),
• remove_newline=False keeps newlines,
• middle-ellipsis on long text.

Verification

$ uv run pytest tests/utils/test_shorten.py -q
13 passed

$ uv run pytest tests/tools/test_extract_key_argument.py -q   # caller, no regression
9 passed

$ uv run ruff check src/kimi_cli/utils/string.py tests/utils/test_shorten.py
All checks passed!

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.