GPU half of sub-arc 2. When the gutter is on, each line carrying a
diagnostic gets a thin severity-colored bar at the gutter's left edge —
the GPU analogue of the TUI's leading-column E/W/I/H sign glyph. No
protocol change: the per-line severity comes from `current_decorations`,
already frontend-side.
- collect_gutter_sign_rects: per visible line (layout_runs), find the
most-severe diagnostic decoration overlapping that line's byte range and
push a `GUTTER_SIGN_W`-wide full-line-height quad at `GUTTER_SIGN_X`,
colored via decoration_kind_to_underline_color. Most-severe wins
(diagnostic_severity_rank; min rank). Gated on line_numbers, mirroring
the TUI (signs ride the line-number gutter).
- The bars ride the existing background quad batch
(decoration_background_vertex_bytes), so no new pipeline.
Headless render test asserts a diagnostic adds ink with the gutter on.
fmt + clippy --all-targets clean; 54 pmacs-gpu tests pass (render tests on
the local adapter). Needs a GPU eyeball before the sub-arc 2 PR.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014TXbAwk27agwhrNNrhLi2U
Levi Neuwirth
d941bf176b