Window boards: never search a connection ending outside the window

With items away from the window left off its board, a stub from the window
edge out to a rerouted net's far pin crossed copper the exact check never
saw: 38 shorts on th-eda's flight controller. A connection with an end
outside the bounds is now left unrouted, and a window whose new copper
leaves the window is refused.

src/freeroute/route/grid_router.py

@@ -211,6 +211,10 @@ class GridRouter:
         # these nets get connections, and the grid covers only ``bounds``
         # (cells outside it do not exist, so nothing is routed there).
         self.only_nets = frozenset(only_nets) if only_nets is not None else None
+        self._bounds = bounds
+        # connections with an end outside ``bounds``: never searched, since
+        # the grid has no cells to reach that end by
+        self._outside: set[int] = set()
         # Multi-pin nets: pair a net's pin groups by a minimum spanning tree,
         # and let a connection start or end on copper its net already routed
         # (a T into the tree), not only on one chosen pin.
@@ -717,6 +721,8 @@ class GridRouter:
     def _search(
         self, conn: _Connection, allow_ripup: bool, conns: list[_Connection]
     ) -> list[Node] | None:
+        if conn.index in self._outside:
+            return None
         half = self._conn_half(conn)
         self._cur_half, self._spread = half, self._spread_for(half)
         try:
@@ -1872,6 +1878,11 @@ class GridRouter:
         self._net_conns: dict[int, list[_Connection]] = {}
         for conn in conns:
             self._net_conns.setdefault(conn.net_no, []).append(conn)
+        if self._bounds is not None:
+            self._outside = {
+                c.index for c in conns
+                if not (_group_inside(c.a_group, self._bounds) and _group_inside(c.b_group, self._bounds))
+            }
         return conns
 
     def _fixed_pieces(self, net_no: int) -> list[_FixedPiece]:
@@ -2017,6 +2028,19 @@ def _group_label(group) -> str:
     return "/".join(parts) or "?"
 
 
+def _group_inside(group, bounds: IntBox) -> bool:
+    """A group has a pin inside ``bounds``, or a zone reaching into it."""
+    pins, zones = group
+    if any(bounds.ll.x <= p.location.x <= bounds.ur.x and bounds.ll.y <= p.location.y <= bounds.ur.y
+           for p in pins):
+        return True
+    for zone in zones:
+        box = zone.bounding_box()
+        if box.ll.x <= bounds.ur.x and bounds.ll.x <= box.ur.x and box.ll.y <= bounds.ur.y and bounds.ll.y <= box.ur.y:
+            return True
+    return False
+
+
 def _ends_of(conn) -> tuple[str, str]:
     """A readable description of what a connection joins."""
     return _group_label(conn.a_group), _group_label(conn.b_group)

src/freeroute/route/window.py

@@ -206,6 +206,11 @@ def window_reroute(
             after = _open(f for f in sub.failed if f[0] in affected)
             if len(after) >= len(before):
                 continue
+            # the window board left out what lies away from it, so copper
+            # reaching out of the window was never checked against it
+            if any(not _inside((sub.wires.get(n, []), sub.vias.get(n, [])), window)
+                   for n in affected if sub.wires.get(n) or sub.vias.get(n)):
+                continue
             # a net keeping some of its copper is written at one width: the
             # window's new copper has to have gone in at that width too
             if any(

tests/route/test_window_reroute.py

@@ -110,3 +110,19 @@ def test_window_board_keeps_far_items_of_the_rerouted_nets_only():
     refs = {p.component_ref for p in sub.get_pins()}
     assert {"P1", "P2"} <= refs  # net N's pins, though outside the view
     assert not refs & {"Q1", "Q2"}  # net M's, far away, left out
+
+
+def test_a_connection_ending_outside_the_window_gets_no_copper():
+    """Its far end has no grid cells; a stub out to it would cross items the
+    window board never saw."""
+    from freeroute.route.exact_router import route_board_exact
+
+    dsn = parse_dsn(_slot(far=True))
+    s = dsn.resolution.value
+    window = IntBox(70000, -70000, 130000, -30000)  # the slot only; net M's pins are far off
+    result = route_board_exact(
+        build_board(dsn), trace_width=round(_rule_width_dsn(dsn) * s),
+        clearance=round(_rule_clearance_dsn(dsn) * s), only_nets=frozenset({2}), bounds=window,
+    ).result
+    assert [f[0] for f in result.failed] == [2]
+    assert not result.wires.get(2) and not result.vias.get(2)