label: Skip highlights while masked

[violetpurpleish]

Description

Masked labels replace source text with bullets. Applying secondary-text or matching highlight ranges to the masked string can reuse source byte offsets, including offsets that are not valid UTF-8 boundaries in the displayed bullet string and can panic during rendering. Styled ranges can also reveal information about the structure of concealed text.

Skip highlight measurement entirely while a Label is masked. This keeps every bullet visually uniform, avoids unnecessary matching and range conversion work, and leaves unmasked highlighting behavior unchanged.

The Label Story now includes a Mask toggle in the Highlighting section so the interaction can be tested directly. The existing balance example is restored to its original content.

Public API

No API signatures change. Label::masked(true) now suppresses all highlight styles, including matching highlights and primary/secondary color segmentation.

Behavior Change

Masked labels no longer preserve visible highlight colors. This is intentional: concealed text should not expose matching or segment boundaries. Unmasking restores the configured highlights.

How to Test

• cargo test -p gpui-component --features test-support --lib --locked: 556 passed.
• cargo check -p gpui-component-story --locked: passed.
• Label Story > Highlighting: enter a matching query, toggle Mask on, and verify all bullets use a uniform style with no highlighted segment. Toggle Mask off and verify the matching highlight returns.

AI-assisted implementation with Codex; diff reviewed and regression checks run.