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.

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)