Route wider net classes at their width, falling back where they don't fit

The grid is laid out for the default width; a wider trace also needs the
cells its extra half width reaches to be free, and claims a wider halo.
A connection that does not fit at its class width (typically at a
fine-pitch pin) is routed at the default instead and reported. A net is
written at its class width when all of its connections went in at it,
and the exact check verifies it at that width; nets that shove or the
diagonal pass reshaped go out at the default.

src/freeroute/route/pipeline.py

@@ -34,6 +34,25 @@ def _rule_width_dsn(dsn: DsnBoard) -> float:
     return rules[0].value if rules else _DEFAULT_WIDTH_DSN
 
 
+def _net_widths_board(dsn: DsnBoard, scale: int) -> dict[int, int]:
+    """Track width of every net whose class asks for more than the default,
+    in board units, by net number (build_board numbers nets in DSN order)."""
+    default = _rule_width_dsn(dsn)
+    by_name: dict[str, float] = {}
+    for net_class in dsn.net_classes:
+        if not net_class.width_rules:
+            continue
+        width = net_class.width_rules[0].value
+        if width > default:
+            for name in net_class.net_names:
+                by_name[name] = max(by_name.get(name, 0.0), width)
+    return {
+        i + 1: round(by_name[net.name] * scale)
+        for i, net in enumerate(dsn.nets)
+        if net.name in by_name
+    }
+
+
 def _rule_clearance_dsn(dsn: DsnBoard) -> float:
     for rule in dsn.structure_rules.clearance_rules:
         if not rule.class_pairs:  # the layer-wide default clearance
@@ -108,6 +127,7 @@ def route_dsn_board(
         route_first=route_first,
         access_cost=access_cost,
         rollback=rollback,
+        net_widths=_net_widths_board(dsn, scale),
     )
     return result, scale, [layer.name for layer in dsn.layers]
 
@@ -122,6 +142,9 @@ def _to_routing_result(route, dsn: DsnBoard, scale: int, layer_names: list[str])
     result = RoutingResult()
     for net_no, segments in route.wires.items():
         name = numbers_to_names.get(net_no, str(net_no))
+        # its class's width when every connection of the net went in at it
+        half = getattr(route, "net_half", {}).get(net_no)
+        net_width = 2 * half / scale if half else width_dsn
         for layer_index, path in segments:
             layer_name = layer_names[layer_index] if layer_index < len(layer_names) else "F.Cu"
             coords: list[float] = []
@@ -129,7 +152,7 @@ def _to_routing_result(route, dsn: DsnBoard, scale: int, layer_names: list[str])
                 coords.append(point.x / scale)
                 coords.append(point.y / scale)
             if len(coords) >= 4:
-                result.add_wire(name, RoutedWire(layer=layer_name, width=width_dsn, coords=coords))
+                result.add_wire(name, RoutedWire(layer=layer_name, width=net_width, coords=coords))
     for net_no, locations in route.vias.items():
         name = numbers_to_names.get(net_no, str(net_no))
         for loc in locations:
@@ -137,6 +160,9 @@ def _to_routing_result(route, dsn: DsnBoard, scale: int, layer_names: list[str])
     result.unrouted = [
         (numbers_to_names.get(n, str(n)), a, b, zone) for n, a, b, zone in getattr(route, "failed", [])
     ]
+    result.narrowed = [
+        (numbers_to_names.get(n, str(n)), a, b) for n, a, b in getattr(route, "narrowed", [])
+    ]
     return result
 
 
@@ -207,6 +233,7 @@ def route_dsn_board_exact(
         route_first=route_first,
         access_cost=access_cost,
         rollback=rollback,
+        net_widths=_net_widths_board(dsn, scale),
     )
     return exact, scale, [layer.name for layer in dsn.layers]