Sub-arc 2 of the UX arc, TUI half. When a window reserves a line-number
gutter, lines with diagnostics get a severity-colored sign glyph (E/W/I/H)
in the gutter's leading column — closing the last deferred Task #23 item.
No protocol/daemon change: the per-line severity is already frontend-side
(the diag store the DiagnosticView already reads).
- `Viewport` gains `gutter_w` so overlays can reach the gutter's leading
column at `cell_origin.col - gutter_w`; the text area is already shifted
past it, so viewport-relative painters stay gutter-agnostic.
- The gutter's number pass now runs *before* the overlays (was after), so
the DiagnosticView can draw its sign into the gutter's blanked leading
column without the number pass erasing it.
- DiagnosticView: with a gutter, draw the severity sign glyph colored by
`underline_color()`; without one, keep the legacy column-0 background
marker (the "fake gutter" that predates a real gutter column). Extracted
to `paint_line_markers` to keep `render` under the line cap.
The number never reaches column 0 (>=1 leading pad by construction), so
sign and number coexist. Diagnostic signs currently ride the line-number
gutter (visible when line numbers are on); a signs-without-numbers mode is
deferred.
Test: gutter_sign_replaces_the_column_marker_when_a_gutter_is_reserved.
Validated: fmt + clippy --all-targets clean both flavors; 1441 lib + 22
diag tests pass. Needs a TUI eyeball before the GPU half.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014TXbAwk27agwhrNNrhLi2U
M4.6 follow-up piece 2. `Style` gains `underline_color: Color`
(Default = follow the text color) so a diagnostic squiggle can be
red/yellow/cyan/gray without clobbering the syntax color of the
text it underlines — exactly why error_style() left its 'red'
unwired until now.
The wire consequence: Style rides inside Cell / CellDelta /
Snapshot / StyleSpans, so this is the protocol's first
encoding-breaking change. PROTOCOL_VERSION 5 → 6 and
SUPPORTED_PROTOCOL_VERSIONS narrows to [6]: postcard is not
self-describing, so no per-session send gate can keep a v5 peer
decoding v6 cells — a mismatched pair now fails the handshake with
a clean VersionMismatch instead of garbling mid-session. Version
policy tests rewritten to pin the new contract.
Surface wiring:
- diag.rs: per-severity underline_color (indexed 1/3/6/8).
- frontend.rs: kitty-style CSI 4:N for Double/Curly/Dotted/Dashed
(previously flattened to plain SGR 4) + SGR 58:5/58:2 emission.
- ansi.rs: parse SGR 58/59 with the 38/48 extended-color grammar.
- overlay.rs merge_styles: non-default-wins, like fg/bg/underline.
- lua_bindings.rs: underline_color on Lua style tables.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Levi Neuwirth