perf: let one tessellation serve every background

Switching to a Layout re-tessellated the whole model — `memo_miss=186455`,
2034 ms — to arrive at geometry identical to what was already in the memo.
The only thing that differed was colour.

`local_wires_for` already knows this: it stores the raw colour and drops
its background argument with `let _ = bg_color;`, noting that
`Batches::finalize` applies `adapt_to_bg` last, "so the cache no longer
has to rebuild on BACKGROUND / layout-switch". The tessellation memo's
guard had not been told, and still mixed the background in, so every
entry was discarded on a switch.

`finalize` now records what its colour resolution consumed — the raw
colour, the raw glyph colours, and the three flags it branches on — as
`WireModel::bg_adapt`, and `resolve_colors_for_bg` replays it for another
background. The guard drops the background, so a memo entry serves any
layout.

The resolution recomputes from the recorded raw colour rather than from
the resolved one, which makes it idempotent and therefore safe over a set
that mixes memo hits with freshly tessellated misses. Re-adapting the
resolved colour would not be safe: `adapt_to_bg` snaps a near-white colour
to pure black on a light background, and pure black comes back pure
*white* on a dark one, losing the tint. A test pins that asymmetry so the
raw colour is not optimised away later.

The contract is tested against the real `finalize` rather than a copy of
its logic: for every background pair, building under one and resolving for
the other lands exactly where building under the other would have.

`bg_adapt` is `None` for wires built anywhere else, and the resolution
skips them, so nothing outside the block cache changes colour. It is also
`None` when the resolution would be a no-op — a preserved colour with no
canvas fill looks the same under every background — which keeps the common
case at no cost.

Ordering is unchanged: the pass runs inside the builder, before
`append_scene_markers` and `apply_refedit_fade`, both of which have their
own separate background dependency.

`wires-build` gains `colors=` so the pass has a number of its own.

Co-Authored-By: Claude Opus 5 <[email protected]>

src/modules/annotate/aligned_dim.rs

@@ -286,6 +286,7 @@ impl CadCommand for AlignedDimensionCommand {
         let p1 = p1.as_vec3();
         let p2 = p2.as_vec3();
         Some(WireModel {
+            bg_adapt: None,
             point_marker: None,
             taper_widths: Vec::new(),
             pattern_stations: Vec::new(),
@@ -348,6 +349,7 @@ fn preview_aligned(p1: DVec3, p2: DVec3, dim_pt: DVec3) -> WireModel {
     let half_height = 0.16;
     let to_point = |point: DVec3| point.as_vec3().to_array();
     WireModel {
+        bg_adapt: None,
         point_marker: None,
         taper_widths: Vec::new(),
         pattern_stations: Vec::new(),

src/modules/annotate/angular_dim.rs

@@ -1132,6 +1132,7 @@ fn nan() -> DVec3 {
 
 fn preview_wire(points: Vec<DVec3>) -> WireModel {
     WireModel {
+        bg_adapt: None,
         point_marker: None,
         taper_widths: Vec::new(),
         pattern_stations: Vec::new(),

src/modules/annotate/data_link.rs

@@ -63,6 +63,7 @@ impl DataLinkPlaceCommand {
             );
         }
         WireModel {
+            bg_adapt: None,
             point_marker: None,
             taper_widths: Vec::new(),
             pattern_stations: Vec::new(),

src/modules/annotate/diameter_dim.rs

@@ -272,6 +272,7 @@ fn dvec(point: Vector3) -> DVec3 {
 fn preview_line(far_chord: Vec3, chord: Vec3, text: Vec3) -> WireModel {
     let separator = [f32::NAN; 3];
     WireModel {
+        bg_adapt: None,
         point_marker: None,
         taper_widths: Vec::new(),
         pattern_stations: Vec::new(),

src/modules/annotate/dim_baseline.rs

@@ -709,6 +709,7 @@ fn preview_for_dimension(dimension: &Dimension) -> WireModel {
         _ => {}
     }
     WireModel {
+        bg_adapt: None,
         point_marker: None,
         taper_widths: Vec::new(),
         pattern_stations: Vec::new(),

src/modules/annotate/dimjogline.rs

@@ -86,6 +86,7 @@ impl CadCommand for DimJogLineCommand {
         }
         let d = 0.3_f32;
         Some(WireModel {
+            bg_adapt: None,
             point_marker: None,
             taper_widths: Vec::new(),
             pattern_stations: Vec::new(),

src/modules/annotate/dimtedit.rs

@@ -103,6 +103,7 @@ impl CadCommand for DimTeditCommand {
         }
         let d = 0.2_f32;
         Some(WireModel {
+            bg_adapt: None,
             point_marker: None,
             taper_widths: Vec::new(),
             pattern_stations: Vec::new(),

src/modules/annotate/jogged_radius_dim.rs

@@ -442,6 +442,7 @@ fn dvec(point: Vector3) -> DVec3 {
 
 fn preview_wire(points: Vec<Vec3>) -> WireModel {
     WireModel {
+        bg_adapt: None,
         point_marker: None,
         taper_widths: Vec::new(),
         pattern_stations: Vec::new(),

src/modules/annotate/leader_cmd.rs

@@ -300,6 +300,7 @@ fn preview_wire(pts: &[Vec3], arrow_size: f32) -> WireModel {
         points.push([w2.x, w2.y, w2.z]);
     }
     WireModel {
+        bg_adapt: None,
         point_marker: None,
         taper_widths: Vec::new(),
         pattern_stations: Vec::new(),

src/modules/annotate/linear_dim.rs

@@ -467,6 +467,7 @@ fn ocs_point(point: [f64; 2], elevation: f64, normal: Vector3) -> DVec3 {
 
 fn preview_wire(points: Vec<DVec3>) -> WireModel {
     WireModel {
+        bg_adapt: None,
         point_marker: None,
         taper_widths: Vec::new(),
         pattern_stations: Vec::new(),

src/modules/annotate/mleader_cmd.rs

@@ -764,6 +764,7 @@ fn preview_wire(pts: &[Vec3], arrow_size: f32) -> WireModel {
         points.push([w2.x, w2.y, w2.z]);
     }
     WireModel {
+        bg_adapt: None,
         point_marker: None,
         taper_widths: Vec::new(),
         pattern_stations: Vec::new(),

src/modules/annotate/mleader_edit.rs

@@ -490,6 +490,7 @@ impl CadCommand for MLeaderCollectCommand {
 
 fn preview_wire(pts: &[Vec3]) -> WireModel {
     WireModel {
+        bg_adapt: None,
         point_marker: None,
         taper_widths: Vec::new(),
         pattern_stations: Vec::new(),

src/modules/annotate/ordinate_dim.rs

@@ -270,6 +270,7 @@ fn is_x_type(feature: DVec3, leader: DVec3) -> bool {
 
 fn preview_wire(points: Vec<Vec3>) -> WireModel {
     WireModel {
+        bg_adapt: None,
         point_marker: None,
         taper_widths: Vec::new(),
         pattern_stations: Vec::new(),

src/modules/annotate/radius_dim.rs

@@ -277,6 +277,7 @@ fn dvec(point: Vector3) -> DVec3 {
 
 fn preview_wire(points: Vec<Vec3>) -> WireModel {
     WireModel {
+        bg_adapt: None,
         point_marker: None,
         taper_widths: Vec::new(),
         pattern_stations: Vec::new(),

src/modules/annotate/table_cmd.rs

@@ -212,6 +212,7 @@ impl TableCommand {
             );
         }
         WireModel {
+            bg_adapt: None,
             point_marker: None,
             taper_widths: Vec::new(),
             pattern_stations: Vec::new(),

src/modules/annotate/tolerance_cmd.rs

@@ -81,6 +81,7 @@ impl CadCommand for ToleranceCommand {
             }));
         }
         Some(WireModel {
+            bg_adapt: None,
             point_marker: None,
             taper_widths: Vec::new(),
             pattern_stations: Vec::new(),