bug(cdk/text-field/autosize): Scrollbar appears when line-height is a decimal and autosizing is enabled

[ajitesh-copperleaf]

Is this a regression?

• Yes, this behavior used to work in the previous version

The previous version in which this bug was not present was

No response

Description

When using a <textarea> with cdkTextareaAutosize and a decimal numeric line-height value (for example 1.15), a vertical scrollbar appears even when the content fits perfectly within the view.
This happens despite autosizing being enabled, and the field should automatically expand to fit content without a scrollbar.

This issue does not occur when line-height is an integer (e.g. 1 or 2).

Technical Observation
The browser appears to truncates decimal values internally (e.g. from 16.08 px to 16 px) when returning the clone's height to Angular.
As a result, when the text area expands to its autosized height (e.g. 4 lines), the truncation introduces a small pixel mismatch, just enough to trigger a scrollbar.

Possible solution:
Angular CDK might need to account for fractional pixel rounding when computing textarea height.

Reproduction

StackBlitz link: https://stackblitz.com/edit/5xmbl7sj-53y6s3u8?file=src%2Fexample%2Ftext-field-autosize-textarea-example.html
Steps to reproduce:

1. Open the StackBlitz link above
2. Set the browser zoom to 110% (important)
3. Observe the <textarea> component with cdkTextareaAutosize
4. Notice the CSS rule applied

textarea { line-height: 1.15 }

5. Fill in three lines of text, e.g. using

aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa

6. Add one more character (a),
   -> A scroll bar appears even though the text area expands correctly

Expected Behavior

The textarea should never display a scrollbar when autosizing is enabled, regardless of line-height precision.

It should fully expand to fit content, even when line-height includes decimal or sub-pixel values.

Actual Behavior

A vertical scrollbar appears after the text fills exactly three lines and one additional character is entered.

The scrollbar is triggered despite autosizing correctly adjusting the height.

Environment

• Angular: 20.2.4
• CDK/Material: 20.2.2
• Browser(s): Edge (141.0.3537.85), Chrome (141.0.7390.108) possibly more (tested on these)
• Operating System (e.g. Windows, macOS, Ubuntu): Windows