pcb/scripts/finalize_routing.py

#!/usr/bin/env python3
"""Import a Specctra session and install audited RF/USB copper.

Freerouting is used only for the dense non-critical interconnect.  The GPS
front end and USB2 pair are removed from that result and rebuilt here with
deterministic geometry derived from the selected JLC08161H-3313 stackup.
"""

from __future__ import annotations

import argparse
import math
import shutil
from pathlib import Path

import pcbnew

import finish_signal_routes
import route_local_power
import stitch_plane_pads

ROOT = Path(__file__).resolve().parents[1]
POWER_LOCAL = ROOT / "hardware" / "board_power_local.kicad_pcb"
ROUTED = ROOT / "hardware" / "board_routed.kicad_pcb"

RF_NETS = {"RF_SMA", "RF_PRE_SAW", "RF_POST_SAW", "MAX_MIXIN_HI"}
USB_NETS = {"USB_D_P", "USB_D_N", "FTDI_D_P", "FTDI_D_N"}
CRITICAL_NETS = RF_NETS | USB_NETS


def mm(value: float) -> int:
    return pcbnew.FromMM(value)


def point(x: float, y: float) -> pcbnew.VECTOR2I:
    return pcbnew.VECTOR2I_MM(x, y)


def remove(board: pcbnew.BOARD, item) -> None:
    """Remove and disown a board item.

    pcbnew's BOARD.Remove() does not clear the SWIG "thisown" flag, so the
    Python wrapper still believes it owns the now-freed C++ object. Letting
    the garbage collector finalize it later double-frees that memory and
    corrupts the process (subsequent pcbnew calls start returning raw,
    unusable SwigPyObject instances instead of typed wrappers). Explicitly
    disowning the wrapper right after removal avoids that.
    """
    board.Remove(item)
    item.thisown = False


def footprint(board: pcbnew.BOARD, ref: str) -> pcbnew.FOOTPRINT:
    item = board.FindFootprintByReference(ref)
    if item is None:
        raise RuntimeError(f"Missing footprint {ref}")
    return item


def pads(board: pcbnew.BOARD, ref: str, number: str) -> list[pcbnew.PAD]:
    result = [pad for pad in footprint(board, ref).Pads() if pad.GetNumber() == str(number)]
    if not result:
        raise RuntimeError(f"Missing pad {ref}.{number}")
    return result


def pad_xy(board: pcbnew.BOARD, ref: str, number: str, index: int = 0) -> tuple[float, float]:
    position = pads(board, ref, number)[index].GetPosition()
    return pcbnew.ToMM(position.x), pcbnew.ToMM(position.y)


def assert_ref_nets(board: pcbnew.BOARD, ref: str, expected: set[str]) -> None:
    actual = {pad.GetNetname() for pad in footprint(board, ref).Pads() if pad.GetNetname()}
    if actual != expected:
        raise RuntimeError(f"{ref} net mismatch: expected {sorted(expected)}, got {sorted(actual)}")


def add_segment(board: pcbnew.BOARD, net_name: str,
                start: tuple[float, float], end: tuple[float, float],
                width: float, layer: int = pcbnew.F_Cu, locked: bool = True) -> None:
    if start == end:
        return
    track = pcbnew.PCB_TRACK(board)
    track.SetStart(point(*start))
    track.SetEnd(point(*end))
    track.SetWidth(mm(width))
    track.SetLayer(layer)
    track.SetNet(board.FindNet(net_name))
    track.SetLocked(locked)
    board.Add(track)


def add_polyline(board: pcbnew.BOARD, net_name: str,
                 vertices: list[tuple[float, float]], width: float,
                 layer: int = pcbnew.F_Cu) -> None:
    for start, end in zip(vertices, vertices[1:]):
        add_segment(board, net_name, start, end, width, layer)


def add_via(board: pcbnew.BOARD, net_name: str, position: tuple[float, float],
            diameter: float = 0.45, drill: float = 0.225) -> None:
    via = pcbnew.PCB_VIA(board)
    via.SetPosition(point(*position))
    via.SetWidth(mm(diameter))
    via.SetDrill(mm(drill))
    via.SetLayerPair(pcbnew.F_Cu, pcbnew.B_Cu)
    via.SetNet(board.FindNet(net_name))
    via.SetLocked(True)
    board.Add(via)


def remove_critical_routes(board: pcbnew.BOARD) -> int:
    doomed = [item for item in board.GetTracks() if item.GetNetname() in CRITICAL_NETS]
    for item in doomed:
        remove(board, item)
    return len(doomed)


def remove_temporary_keepouts(board: pcbnew.BOARD) -> int:
    doomed = [zone for zone in board.Zones()
              if zone.GetIsRuleArea() and zone.GetZoneName().startswith("TEMP_")]
    for zone in doomed:
        remove(board, zone)
    return len(doomed)


def route_rf(board: pcbnew.BOARD) -> None:
    # 0.164-mm L1 CPWG with 0.200-mm ground gap: 49.65 ohms on the exact
    # JLC08161H-3313 L1/L2 dielectric construction.
    for ref, expected in {
        "C83": {"RF_SMA", "RF_PRE_SAW"},
        "C84": {"RF_POST_SAW", "GND"},
        "R39": {"RF_POST_SAW", "MAX_MIXIN_HI"},
        "C85": {"MAX_MIXIN_HI", "GND"},
    }.items():
        assert_ref_nets(board, ref, expected)

    w = 0.164
    j2 = pad_xy(board, "J2", "1")
    j2_inner = (j2[0] - 0.50, j2[1])
    dc_block_1 = pad_xy(board, "C83", "1")
    l4_2 = pad_xy(board, "L4", "2")
    add_polyline(board, "RF_SMA", [j2_inner, (170.10, 42.09), l4_2, dc_block_1], w)
    # D1 sits directly on the 50-ohm line: its pad 1 overlaps the run above,
    # so no spur is drawn.  On a 1.34-mm stub the 0.3-pF clamp presented
    # -j228 ohm at L1 and cost 3.4 dB of return loss for nothing.

    add_polyline(board, "RF_PRE_SAW",
                 [pad_xy(board, "C83", "2"), pad_xy(board, "FL1", "1")], w)

    fl_out = pad_xy(board, "FL1", "4")
    tune1 = pad_xy(board, "C84", "1")
    series_1 = pad_xy(board, "R39", "1")
    add_polyline(board, "RF_POST_SAW", [fl_out, tune1, series_1], w)

    series_2 = pad_xy(board, "R39", "2")
    mixin = pad_xy(board, "U21", "25")
    add_polyline(board, "MAX_MIXIN_HI",
                 [series_2, (159.69, 41.80), (mixin[0], 41.80), mixin], w)
    tune2 = pad_xy(board, "C85", "1")
    add_polyline(board, "MAX_MIXIN_HI", [tune2, (tune2[0], 41.80)], w)


def route_usb(board: pcbnew.BOARD) -> None:
    # Main device-side pair uses the upper receptacle contact pair.  The two
    # mirrored USB-C contacts join through a sub-1.5-mm L3 crossover so neither
    # polarity creates a same-layer crossing at the receptacle.
    w = 0.135
    for ref, expected in {
        "R62": {"USB_D_P", "FTDI_D_P"},
        "R63": {"USB_D_N", "FTDI_D_N"},
    }.items():
        assert_ref_nets(board, ref, expected)

    dm_main, dp_main = pad_xy(board, "J1", "B7"), pad_xy(board, "J1", "A6")
    dm_mirror, dp_mirror = pad_xy(board, "J1", "A7"), pad_xy(board, "J1", "B6")
    dm_join, dp_join = (28.60, 47.25), (29.20, 47.75)
    dm_aux, dp_aux = (27.60, 48.25), (28.20, 48.75)

    add_polyline(board, "USB_D_N", [dm_main, dm_join], w)
    add_polyline(board, "USB_D_P", [dp_main, dp_join], w)
    add_polyline(board, "USB_D_N", [dm_mirror, dm_aux], w)
    add_polyline(board, "USB_D_P", [dp_mirror, dp_aux], w)
    for net, location in (("USB_D_N", dm_join), ("USB_D_P", dp_join),
                          ("USB_D_N", dm_aux), ("USB_D_P", dp_aux)):
        add_via(board, net, location)
    add_polyline(board, "USB_D_N", [dm_aux, dm_join], w, pcbnew.In2_Cu)
    add_polyline(board, "USB_D_P", [dp_aux, dp_join], w, pcbnew.In2_Cu)

    # Down the free channel east of J1 into the TPD2EUSB30A clamp pads.  D_P
    # drops at x=30.00 rather than on its own pad column so it keeps 0.2325 mm
    # to the D_N clamp pad, then jogs 45 degrees onto U6.1.
    dm_esd = pad_xy(board, "U6", "3")
    dp_esd = pad_xy(board, "U6", "1")
    add_polyline(board, "USB_D_N",
                 [dm_join, (29.60, 47.25), (30.50, 48.15), dm_esd], w)
    add_polyline(board, "USB_D_P",
                 [dp_join, (29.45, 47.75), (30.00, 48.30),
                  (30.00, 51.775), dp_esd], w)

    # Both clamp taps run as a 0.5-mm-pitch 45-degree pair to the series
    # terminators.  D_N leaves U6.3 straight east; D_P has to step south first,
    # because U6.2 (ground) sits directly east of U6.1 on the same pad row.
    dm_r = pad_xy(board, "R63", "1")
    dp_r = pad_xy(board, "R62", "1")
    add_polyline(board, "USB_D_N",
                 [dm_esd, (31.000, 51.075), (34.425, 54.50), dm_r], w)
    add_polyline(board, "USB_D_P",
                 [dp_esd, (30.150, 52.500), (31.718, 52.500),
                  (34.718, 55.50), dp_r], w)

    # Equal short post-termination legs into the FT4232H USB PHY.
    add_polyline(board, "FTDI_D_N",
                 [pad_xy(board, "R63", "2"), (37.76, 54.75), pad_xy(board, "U2", "7")], w)
    add_polyline(board, "FTDI_D_P",
                 [pad_xy(board, "R62", "2"), (37.76, 55.25), pad_xy(board, "U2", "8")], w)


def add_rf_ground(board: pcbnew.BOARD) -> None:
    zone = pcbnew.ZONE(board)
    zone.SetLayer(pcbnew.F_Cu)
    zone.SetNet(board.FindNet("GND"))
    zone.SetLocalClearance(mm(0.20))
    zone.SetMinThickness(mm(0.10))
    zone.SetPadConnection(pcbnew.ZONE_CONNECTION_FULL)
    zone.SetIslandRemovalMode(pcbnew.ISLAND_REMOVAL_MODE_NEVER)
    zone.SetAssignedPriority(100)
    outline = zone.Outline()
    outline.NewOutline()
    for x, y in ((152.0, 36.0), (174.5, 36.0), (174.5, 49.5), (152.0, 49.5)):
        outline.Append(point(x, y))
    board.Add(zone)

    # J2 uses separate top- and bottom-side SMT lands with the same pad number.
    # The top lands overlap the RF ground zone, but a bottom land whose centre
    # is outside the outline cannot acquire a thermal from the board-wide B.Cu
    # pour.  Start inside each 1.5-mm-wide land and stop far enough inboard for
    # the existing B.Cu pour to absorb the bond.  At x=174.50 a 0.40-mm track
    # retains 0.30 mm to the x=175.00 routed edge (rule minimum 0.25 mm).
    for y in (37.75, 46.25):
        add_segment(board, "GND", (174.50, y), (173.50, y),
                    0.40, pcbnew.B_Cu)

    # Lambda/20 is about 9.5 mm at GPS L1 in FR-4.  This 2-mm fence is much
    # tighter and also gives every local shunt/EP a short plane connection.
    fence = [(x, 38.7) for x in range(153, 174, 2)]
    fence += [(x, 45.0) for x in range(161, 174, 2)]
    existing_vias = [item for item in board.GetTracks()
                     if isinstance(item, pcbnew.PCB_VIA)]
    # The fence goes in after the session has been imported, so by now there is
    # routed copper on F.Cu and B.Cu inside this region as well.  Checking only
    # vias and pads let a fence via land straight on top of a signal trace.
    other_tracks = [item for item in board.GetTracks()
                    if not isinstance(item, pcbnew.PCB_VIA)
                    and item.GetNetname() != "GND"]
    all_pads = [pad for fp in board.GetFootprints() for pad in fp.Pads()]
    via_radius = 0.225 + 0.10
    for location in fence:
        candidate = point(*location)
        blocked = any(
            item.GetNetname() != "GND" and
            math.hypot(pcbnew.ToMM(item.GetPosition().x - candidate.x),
                       pcbnew.ToMM(item.GetPosition().y - candidate.y)) < 0.75
            for item in existing_vias
        )
        if not blocked:
            x, y = location
            for pad in all_pads:
                if pad.GetNetname() == "GND":
                    continue
                box = pad.GetBoundingBox()
                if (pcbnew.ToMM(box.GetX()) - 0.35 <= x <= pcbnew.ToMM(box.GetRight()) + 0.35 and
                        pcbnew.ToMM(box.GetY()) - 0.35 <= y <= pcbnew.ToMM(box.GetBottom()) + 0.35):
                    blocked = True
                    break
        if not blocked:
            for item in other_tracks:
                start, end = item.GetStart(), item.GetEnd()
                reach = via_radius + pcbnew.ToMM(item.GetWidth()) / 2
                if route_local_power.segment_distance(location,
                                    (pcbnew.ToMM(start.x), pcbnew.ToMM(start.y)),
                                    (pcbnew.ToMM(end.x), pcbnew.ToMM(end.y))) < reach:
                    blocked = True
                    break
        if not blocked:
            add_via(board, "GND", location, 0.45, 0.225)


NETCLASS_WIDTH = {"Default": 0.12, "BGA_ESCAPE": 0.10, "CLOCK": 0.15,
                  "POWER": 0.40}


MIN_TRACK_WIDTH = 0.10
MIN_CLEARANCE = 0.10

# These local rails carry bias or IC-internal supply current and may safely use
# the finisher's 0.25-mm POWER width.  The 5-V input paths and FPGA rails are
# deliberately absent: they must be completed by the plane/local-power stage
# at their full width, never "made connected" with a signal-sized neck.
FINE_POWER_NETS = {
    "FTDI_1V8", "FTDI_VPHY", "FTDI_VPLL",
    "IMU_3V3", "IMU_VREGA2", "IMU_VREGD",
    "ANT_BIAS_SEL", "ANT_BIAS_SW",
}


def normalize_imported_widths(board: pcbnew.BOARD) -> tuple[int, int]:
    """Restore the net class width on copper the session came back too thin.

    Freerouting's auto-routing stage honours the DSN rule width exactly, but
    its fanout stage emits three quarters of it, which lands below this board's
    0.10-mm minimum track width.  The affected pieces are the short stubs at
    the pads, and widening one can walk it into a neighbouring pad, so each is
    grown only as far as it still clears everything else - the class width
    where there is room, the board minimum where there is not.
    """
    obstacles = route_local_power.Obstacles(board)
    doomed = []
    widened = 0
    for item in board.GetTracks():
        if isinstance(item, pcbnew.PCB_VIA) or item.IsLocked():
            continue
        target = NETCLASS_WIDTH.get(item.GetNetClassName())
        if target is None or pcbnew.ToMM(item.GetWidth()) >= target - 1e-6:
            continue
        start = (pcbnew.ToMM(item.GetStart().x), pcbnew.ToMM(item.GetStart().y))
        end = (pcbnew.ToMM(item.GetEnd().x), pcbnew.ToMM(item.GetEnd().y))
        for width in (target, MIN_TRACK_WIDTH):
            # Judge existing copper against the rule itself, not the extra
            # margin the local router leaves itself when placing new copper.
            if obstacles.track_clear(item.GetNetname(), start, end,
                                     width, item.GetLayer(),
                                     clearance_floor=MIN_CLEARANCE):
                item.SetWidth(mm(width))
                widened += 1
                break
        else:
            # Nothing legal fits here, so this piece cannot ship.  Dropping it
            # unravels its net back to the pads, and the completion pass
            # further down rebuilds the connection at the proper width.
            doomed.append(item)
    for item in doomed:
        remove(board, item)
    return widened, len(doomed)


def remove_dangling_copper(board: pcbnew.BOARD) -> tuple[int, int]:
    """Delete copper the finished routing left hanging.

    A ball whose net ended up routed entirely on F.Cu leaves its pre-routed
    dogbone via connected on one layer only, and removing that via in turn
    strands the stub that fed it.  Both are drilled holes and copper with no
    purpose, so this repeats until nothing new comes loose.
    """
    vias = tracks = 0
    for _round in range(8):
        board.BuildConnectivity()
        connectivity = board.GetConnectivity()
        doomed = [item for item in board.GetTracks()
                  if item.GetNetname() not in CRITICAL_NETS
                  and connectivity.TestTrackEndpointDangling(item, False)]
        if not doomed:
            break
        for item in doomed:
            if isinstance(item, pcbnew.PCB_VIA):
                vias += 1
            else:
                tracks += 1
            remove(board, item)
    board.BuildConnectivity()
    return vias, tracks


def drop_plane_islands(board: pcbnew.BOARD) -> int:
    """Discard unconnected plane fragments left by the escape via anti-pads.

    The generated planes keep every fragment while the board is unrouted so the
    Specctra export still shows the router a plane target under each via field.
    A finished board must not ship floating copper, so the final fill removes
    any island the completed routing did not connect.
    """
    changed = 0
    for zone in board.Zones():
        if zone.GetIsRuleArea() or zone.GetNetname() == "":
            continue
        zone.SetIslandRemovalMode(pcbnew.ISLAND_REMOVAL_MODE_ALWAYS)
        changed += 1
    return changed


def add_named_rule_areas(board: pcbnew.BOARD) -> None:
    """Permanent named areas that only exist so custom DRC rules can name them.

    The TPD2EUSB30A is a SOT-23 clamp whose ground pad sits between its two
    channel pads, so USB_D_P and USB_D_N must separate for about 1.5 mm to pass
    it.  That is normal for this package, but it does break the 0.90-mm coupled
    gap the pair holds everywhere else, so the rule is scoped to skip this one
    breakout instead of being relaxed board-wide.

    RF_NO_DIGITAL names the region under the GPS front end.  The TEMP_ version
    of it exists only while the autorouter runs, so once that is deleted
    nothing would stop a later hand edit from dropping a digital trace onto L3,
    L5, L6 or B.Cu directly under the RF line.  A plain keepout cannot be used
    here because it would also reject the ground stitching vias and the
    MAX2771's own supply drops, so the area carries no constraint itself and
    board.kicad_dru scopes the disallow to non-power net classes.  It
    deliberately stops short of L2 and L7: those must stay solid and unbroken
    under the RF path, which is exactly what an unrouted plane layer gives.
    """
    below = pcbnew.LSET()
    for layer in (pcbnew.In2_Cu, pcbnew.In3_Cu, pcbnew.In4_Cu, pcbnew.In5_Cu, pcbnew.In7_Cu, pcbnew.In8_Cu, pcbnew.B_Cu):
        below.AddLayer(layer)
    top = pcbnew.LSET()
    top.AddLayer(pcbnew.F_Cu)
    areas = (
        ("USB_ESD_BREAKOUT", (29.90, 50.70, 32.10, 53.10), top),
        ("RF_NO_DIGITAL", (152.00, 36.00, 174.50, 43.70), below),
    )
    for name, bounds, layers in areas:
        x0, y0, x1, y1 = bounds
        area = pcbnew.ZONE(board)
        area.SetZoneName(name)
        area.SetIsRuleArea(True)
        area.SetLayerSet(layers)
        area.SetDoNotAllowTracks(False)
        area.SetDoNotAllowVias(False)
        area.SetDoNotAllowPads(False)
        area.SetDoNotAllowFootprints(False)
        area.SetDoNotAllowZoneFills(False)
        outline = area.Outline()
        outline.NewOutline()
        for x, y in ((x0, y0), (x1, y0), (x1, y1), (x0, y1)):
            outline.Append(point(x, y))
        board.Add(area)


def add_rf_launch_relief(board: pcbnew.BOARD) -> None:
    """Void the reference planes under the SMA edge-launch pad.

    J2's centre land is 1.5 mm wide because that is what the connector's
    centre pin needs mechanically, but 1.5 mm of copper 0.0994 mm above a
    solid L2_GND is a 10.7-ohm transmission line, not a 50-ohm one.  The
    1.84 mm of it that sits over the plane is 6.7 degrees long at L1 and
    reflects 12 dB - by far the worst discontinuity in the RF path, and worse
    than everything the 0.164-mm line downstream is carefully built to avoid.

    Removing the plane under the land moves its reference down to L4_PWR
    (VCC3V0_RF, an AC ground) 0.587 mm below, which raises the launch to about
    37 ohms and 30 dB.  L3_SIG carries no pour and no copper here, so this
    only has to void L2; the area covers L3 as well so a later edit cannot
    fill the gap back in.  It stops at x = 172.35, where the land ends and the
    0.164-mm line begins, so the line keeps its own L2 reference.
    """
    relief = pcbnew.LSET()
    for layer in (pcbnew.In1_Cu, pcbnew.In2_Cu):     # L2_GND, L3_SIG
        relief.AddLayer(layer)
    area = pcbnew.ZONE(board)
    area.SetZoneName("RF_LAUNCH_RELIEF")
    area.SetIsRuleArea(True)
    area.SetLayerSet(relief)
    area.SetDoNotAllowTracks(True)
    area.SetDoNotAllowVias(True)
    area.SetDoNotAllowZoneFills(True)
    area.SetDoNotAllowPads(False)
    area.SetDoNotAllowFootprints(False)
    outline = area.Outline()
    outline.NewOutline()
    for x, y in ((172.35, 40.95), (175.10, 40.95), (175.10, 43.05), (172.35, 43.05)):
        outline.Append(point(x, y))
    board.Add(area)


def routed_lengths(board: pcbnew.BOARD) -> dict[str, float]:
    totals = {net: 0.0 for net in CRITICAL_NETS}
    for item in board.GetTracks():
        net = item.GetNetname()
        if net not in totals or isinstance(item, pcbnew.PCB_VIA):
            continue
        start, end = item.GetStart(), item.GetEnd()
        totals[net] += math.hypot(pcbnew.ToMM(end.x - start.x), pcbnew.ToMM(end.y - start.y))
    return totals


def main() -> None:
    parser = argparse.ArgumentParser()
    parser.add_argument("session", type=Path, help="Freerouting .ses file")
    parser.add_argument("--base", type=Path, default=POWER_LOCAL,
                        help="Board used to create the routed DSN")
    parser.add_argument("--output", type=Path, default=ROUTED)
    parser.add_argument(
        "--finish-nets", default="",
        help="Comma- or semicolon-separated residual nets to close with the "
             "fine local maze before dangling-copper cleanup; use 'auto' to "
             "consume the local router's exact unresolved-net result",
    )
    args = parser.parse_args()

    board = pcbnew.LoadBoard(str(args.base))
    if not pcbnew.ImportSpecctraSES(board, str(args.session)):
        raise RuntimeError(f"Could not import {args.session}")
    removed = remove_critical_routes(board)
    widened, dropped = normalize_imported_widths(board)
    # Keep imported dogbones and dangling track ends until after the focused
    # finisher.  They are useful legal anchors for the few connections the
    # global router leaves open.  The old ordering deleted those anchors first
    # and then forced every residual route to find a brand-new via beside a
    # fine-pitch pad, which is exactly where there is no room.
    stranded_vias = stranded_tracks = 0
    removed_keepouts = remove_temporary_keepouts(board)
    route_rf(board)
    route_usb(board)
    add_rf_ground(board)
    add_rf_launch_relief(board)
    add_named_rule_areas(board)

    # The reserved RF and USB corridors are gone now, so the power pads that
    # sit inside them can finally reach their planes.  Both passes are the same
    # deterministic code used earlier in the pipeline.
    if not pcbnew.ZONE_FILLER(board).Fill(board.Zones()):
        raise RuntimeError("Zone fill before final power completion failed")
    stitched, _unreachable = stitch_plane_pads.stitch(board)
    if not pcbnew.ZONE_FILLER(board).Fill(board.Zones()):
        raise RuntimeError("Zone fill after final plane stitching failed")
    remaining = route_local_power.complete(board, signals=True)

    requested = [name.strip()
                 for name in args.finish_nets.replace(";", ",").split(",")
                 if name.strip()]
    if requested == ["auto"]:
        candidates = []
        class_priority = {"CLOCK": 0, "BGA_ESCAPE": 1, "Default": 2}
        for name in remaining:
            net = board.FindNet(name)
            if net is None:
                continue
            klass = net.GetNetClassName()
            if klass in {"Default", "BGA_ESCAPE", "CLOCK"} or name in FINE_POWER_NETS:
                # Route the widest/most constrained clocks before ordinary
                # signals can spend their channels; local low-current rails
                # are last because their endpoints are confined to one IC.
                priority = class_priority.get(klass, 3)
                candidates.append((priority, name))
        finish_nets = [name for _priority, name in sorted(candidates)]
        print("Fine-maze residuals:", ", ".join(finish_nets) or "none")
    else:
        finish_nets = requested
    if finish_nets:
        board.BuildConnectivity()
        maze = finish_signal_routes.FineMaze(board)
        for net_name in finish_nets:
            if board.FindNet(net_name) is None:
                raise RuntimeError(f"Unknown --finish-nets entry: {net_name}")
            finish_signal_routes.finish_net(maze, net_name)

    late_vias, late_tracks = remove_dangling_copper(board)
    cleaned = drop_plane_islands(board)
    if not pcbnew.ZONE_FILLER(board).Fill(board.Zones()):
        raise RuntimeError("Final zone fill failed")
    pcbnew.SaveBoard(str(args.output), board)
    for suffix in (".kicad_pro", ".kicad_dru"):
        source = args.base.with_suffix(suffix)
        if source.exists():
            shutil.copyfile(source, args.output.with_suffix(suffix))
    print(f"Removed {removed} autorouted critical-net items")
    print(f"Widened {widened} imported tracks; dropped {dropped} that had no room")
    print(f"Removed {stranded_vias + late_vias} unused vias and "
          f"{stranded_tracks + late_tracks} stranded stubs")
    print(f"Removed {removed_keepouts} temporary critical-route keepouts")
    print("Late plane stitching:",
          ", ".join(f"{n}={k}" for n, k in sorted(stitched.items())) or "none")
    print(f"Enabled island removal on {cleaned} plane zones")
    print(f"Saved {args.output}")
    for net, length in sorted(routed_lengths(board).items()):
        print(f"{net:16s} {length:8.3f} mm")


if __name__ == "__main__":
    main()