[FanWu-ai]

TextArea accepts FilterOrBool for multiline, but its constructor evaluates the filter's truth value. Passing Condition, Always, or Never raises ValueError before the widget can be used.

Resolve the height at layout time and use ConditionalMargin for line numbers and scrollbars. This allows the existing filter to change at runtime while retaining the single-line height and boolean behavior. Clarify the parameter's existing type in the docstring.

Eight new cases cover booleans, constant filters, callable conditions, changing heights/margins, and a running Application where Enter inserts a newline before a toggle and accepts the input afterward.

Validation on Linux / CPython 3.12.14:

• Pristine complete suite: 156 passed; final complete suite: 164 passed.
• Six added cases fail against the original implementation.
• Ruff lint/format, typos, strict mypy for win32/linux/darwin, all 12 pinned hooks, wheel/sdist builds, and git diff --check pass.
• Independent automated review reran all gates and checked 120 boolean rendering/dimension combinations against the original behavior, plus 21 repeated dynamic render transitions. Packaged source matches the tested implementation.

The mypy platform targets are static checks; other interpreter/native OS matrix combinations were not run locally.

Prepared and tested with OpenAI Codex assistance. No human review is claimed.