Keepout exits and rule areas

A route may not leave a cell inside a wire keepout as a wire, nor reach
a pin there by one: it changes layer instead, and the via goes in the
pad. A pin whose every stub enters a keepout is reached by a via only.

A structure keepout named rule_area... (mckicad names KiCad rule areas
so) is checked for overlap only, as KiCad's DRC does, with the free ends
of each wire tested for their round caps.

bench/diagnose.py

@@ -26,6 +26,7 @@ import sys
 from freeroute.board import build_board
 from freeroute.board.search_tree import ShapeSearchTree
 from freeroute.dsn import parse_dsn
+from freeroute.geometry.octagon import overlaps_2d
 from freeroute.route import grid_router
 from freeroute.route.exact_router import route_board_exact
 from freeroute.route.grid_router import GridRouter, _ends_of
@@ -80,13 +81,24 @@ def _capture_conflicts() -> list:
     def conflict(self, box, net_no, layer, clearance, kind="wire"):
         hit = original(self, box, net_no, layer, clearance, kind)
         if hit:
+            # the shape that tripped the check, found the way the check does
+            other = None
             expanded = box.offset(clearance)
-            other = next(
-                (s for s in self.overlapping(expanded)
-                 if s.net_no != net_no and s.on_layer(layer)
-                 and (s.blocks == "all" or s.blocks == kind + "s")),
-                None,
-            )
+            for s in self.overlapping(expanded):
+                if s.net_no == net_no or not s.on_layer(layer):
+                    continue
+                if s.blocks != "all" and s.blocks != kind + "s":
+                    continue
+                if not s.clearance:
+                    if s.tile.overlaps(box):
+                        other = s
+                        break
+                    continue
+                if (s.exact is not None and overlaps_2d(s.exact, expanded)) or (
+                    s.exact is None and s.tile.overlaps(expanded)
+                ):
+                    other = s
+                    break
             log.append((net_no, kind, layer, box, clearance, other))
         return hit
 
@@ -177,10 +189,11 @@ def diagnose(
         if other is None:
             what = "?"
         elif other.net_no == -1:
-            what = "keepout"
+            what = "keepout" if other.clearance else "rule area"
         else:
             what = ("trace/via of " if other.routed else "pad of ") + names.get(other.net_no, "?")
-        short = (clearance - _gap(box, other.tile)) / scale / 1000 if other is not None else 0
+        need = clearance if other is None or other.clearance else 0
+        short = (need - _gap(box, other.tile)) / scale / 1000 if other is not None else 0
         per_net.setdefault(net_no, []).append(
             {"copper": kind, "layer": layer, "against": what, "short_mm": round(short, 4)}
         )