[jeregrine]

Summary

Accept optional GPUI.Text.StyleRun values on code lines and render their colors, weights, and font styles natively. Callers supply ranges in the original line's UTF-16 coordinates; native rendering translates them to UTF-8 byte ranges after expanding tabs. This uses the existing typed text contract without adding a highlighter dependency.

Validate that runs are bounded, sorted, non-overlapping, and on UTF-16 character boundaries. Ordinary code rows now honor the viewer's custom background and foreground; selection retains its high-contrast foreground and existing diff/log row colors remain intact. Omitted styles preserve plain-text lines.

Evidence

Serialization and validation tests cover emoji surrogate boundaries, invalid and overlapping ranges, multiline text, and the 512-run limit. A native Rust regression checks that highlighting def in 😀\tdef lands at the correct byte range after tab expansion. Syntax highlighting and custom code surfaces were also inspected in a native light/dark prototype.

Clean package validation remains blocked in the unchanged transitive gpui-component dependency by incompatible upstream APIs, before compiling this bridge.

Release Notes:

• [GPUI] Added typed code-line styling and custom code-viewer surface colors for application-owned syntax highlighting.