Fix multi-pin wire/owner desync in shove-in-rooms recovery

_shove_recover_room clobbered a net's _Accepted with a fresh one whose
wire_owners held only the just-recovered wire, while its wires list (the
shared result.wires[net_no]) already held earlier committed connections.
That left wire_owners shorter than the parallel wires list, so a later
net's shove either removed the wrong wire's copper from the search tree
(a silent different-net short: copper stayed in the emitted SES but
vanished from the tree, and has_violation falsely certified it clean) or
raised IndexError and aborted the whole route.

Reuse the net's existing _Accepted on recovery so wire_owners stays
parallel to wires. Fixes both the silent DRC violation and the crash
sibling without touching the DRC-clean or determinism invariants.

Also correct the overstated "density win" framing of the shove_channel
fixture: its plain-routing net drop is an artifact of greedy net order,
not a density limit (the same board routes both nets with zero shoves
under a reorder or with the cosmetic seals removed). Reframed the test
and docstring; the genuine sub-cell win remains the wide_door occupancy
packing (shoves == 0).

Regression tests assert the invariant against the emitted output
directly (reconstructed copper tiles), not just the tree that the bug
fooled, plus determinism, no-crash, and the ordering-artifact bound.

src/freeroute/route/room_router.py

@@ -742,12 +742,20 @@ def _shove_recover_room(
         return 0
 
     owners = force_place_owners(net_no, layer, corners, tree, owner, half_width)
-    acc = _Accepted(
+    # Reuse this net's existing registry if it already committed connections, so
-        wires=result.wires.setdefault(net_no, []), vias=result.vias.setdefault(net_no, [])
+    # ``wire_owners`` stays parallel to ``wires``. Clobbering with a fresh
-    )
+    # ``_Accepted`` here would leave ``wire_owners`` shorter than ``wires`` (its
+    # ``result.wires[net_no]`` list already holds the earlier connections),
+    # desyncing the two lists and making a later shove remove the wrong wire's
+    # copper from the tree while it stays in the emitted route.
+    acc = accepted.get(net_no) if accepted is not None else None
+    if acc is None:
+        acc = _Accepted(
+            wires=result.wires.setdefault(net_no, []), vias=result.vias.setdefault(net_no, [])
+        )
+        accepted[net_no] = acc
     result.add_wire(net_no, layer, corners)
     acc.wire_owners.append(owners)
-    accepted[net_no] = acc
     return len(journal) + 1
 
 

tests/dsn/fixtures/rooms_multipin_desync.dsn

@@ -0,0 +1,72 @@
+(pcb "rooms_multipin_desync"
+  (parser
+    (string_quote ")
+    (space_in_quoted_tokens on)
+    (host_cad "freeroute-test")
+    (host_version "1.0")
+  )
+  (resolution um 10)
+  (unit um)
+  (structure
+    (layer F.Cu (type signal) (property (index 0)))
+    (layer B.Cu (type power) (property (index 1)))
+    (boundary
+      (path pcb 0  0 0  300000 0  300000 -100000  0 -100000  0 0)
+    )
+    (keepout "seal_left" (rect F.Cu 0 -100000 2500 0))
+    (keepout "seal_right" (rect F.Cu 297500 -100000 300000 0))
+    (rule (width 2000) (clearance 2000))
+  )
+  (library
+    (padstack Rect_Pad
+      (shape (rect F.Cu -1000 -1000 1000 1000))
+      (shape (rect B.Cu -1000 -1000 1000 1000))
+      (attach off)
+    )
+    (padstack Via
+      (shape (circle F.Cu 1200))
+      (shape (circle B.Cu 1200))
+      (attach off)
+    )
+    (image PAD
+      (pin Rect_Pad 1 0 0)
+    )
+  )
+  (placement
+    (component PAD
+      (place B1 10000 -50000 front 0)
+      (place B2 290000 -50000 front 0)
+      (place Wt1 10000 -30000 front 0)
+      (place Wt2 290000 -30000 front 0)
+      (place M0 90000 -34000 front 0)
+      (place M1 90000 -46000 front 0)
+      (place M2 90000 -70000 front 0)
+      (place X1 40000 -40000 front 0)
+      (place X2 140000 -40000 front 0)
+      (place Yp1 40000 -60000 front 0)
+      (place Yp2 140000 -60000 front 0)
+    )
+  )
+  (network
+    (net NB
+      (pins B1-1 B2-1)
+    )
+    (net NWtop
+      (pins Wt1-1 Wt2-1)
+    )
+    (net NM
+      (pins M0-1 M1-1 M2-1)
+    )
+    (net NX
+      (pins X1-1 X2-1)
+    )
+    (net NY
+      (pins Yp1-1 Yp2-1)
+    )
+    (class default
+      (rule (width 2000) (clearance 2000))
+    )
+  )
+  (wiring
+  )
+)

tests/dsn/fixtures/rooms_multipin_desync_crash.dsn

@@ -0,0 +1,63 @@
+(pcb "rooms_multipin_desync_crash"
+  (parser
+    (string_quote ")
+    (space_in_quoted_tokens on)
+    (host_cad "freeroute-test")
+    (host_version "1.0")
+  )
+  (resolution um 10)
+  (unit um)
+  (structure
+    (layer F.Cu (type signal) (property (index 0)))
+    (layer B.Cu (type power) (property (index 1)))
+    (boundary
+      (path pcb 0  0 0  300000 0  300000 -100000  0 -100000  0 0)
+    )
+    (keepout "seal_left" (rect F.Cu 0 -100000 2500 0))
+    (keepout "seal_right" (rect F.Cu 297500 -100000 300000 0))
+    (keepout "KD" (rect F.Cu 30000 -100000 150000 -75000))
+    (rule (width 2000) (clearance 2000))
+  )
+  (library
+    (padstack Rect_Pad
+      (shape (rect F.Cu -1000 -1000 1000 1000))
+      (shape (rect B.Cu -1000 -1000 1000 1000))
+      (attach off)
+    )
+    (padstack Via
+      (shape (circle F.Cu 1200))
+      (shape (circle B.Cu 1200))
+      (attach off)
+    )
+    (image PAD
+      (pin Rect_Pad 1 0 0)
+    )
+  )
+  (placement
+    (component PAD
+      (place B1 10000 -50000 front 0)
+      (place B2 290000 -50000 front 0)
+      (place M0 30000 -20000 front 0)
+      (place M1 90000 -20000 front 0)
+      (place M2 90000 -70000 front 0)
+      (place X1 40000 -65000 front 0)
+      (place X2 140000 -65000 front 0)
+    )
+  )
+  (network
+    (net NB
+      (pins B1-1 B2-1)
+    )
+    (net NM
+      (pins M0-1 M1-1 M2-1)
+    )
+    (net NX
+      (pins X1-1 X2-1)
+    )
+    (class default
+      (rule (width 2000) (clearance 2000))
+    )
+  )
+  (wiring
+  )
+)

tests/route/test_room_shove.py

@@ -7,11 +7,14 @@ Two opt-in (``shove=True``) upgrades to the continuous expansion-room track:
   decomposition already keeps every door clearance-clear of committed copper, so
   the projection provably reduces to the old clamp where nothing else crosses the
   door — the four foundation fixtures stay byte-for-byte identical.
-* **Shove-in-rooms** is the real continuous, sub-cell win the grid could not do:
+* **Shove-in-rooms** nudges a committed trace aside with the exact shove
-  when a net would be dropped, the committed trace blocking it is nudged aside
+  primitive when a net would otherwise be dropped, so *both* fit through the same
-  with the exact shove primitive so *both* fit through the same channel. The
+  channel. ``rooms_shove_channel`` drops a net under the default greedy net order
-  headline fixture ``rooms_shove_channel`` drops a net without it and routes both
+  and routes both with shove, DRC-clean -- a recovery from greedy ordering (the
-  with it, DRC-clean.
+  same board is plainly routable under a reorder or without its cosmetic seals,
+  see ``test_room_shove_channel_drop_is_ordering_artifact_not_density``), not a
+  genuine density limit. The true sub-cell win is occupancy packing, which the
+  ``rooms_wide_door`` fixture exercises with ``shoves == 0``.
 """
 
 from __future__ import annotations
@@ -24,10 +27,35 @@ import pytest
 from freeroute.board import build_board
 from freeroute.dsn import parse_dsn
 from freeroute.dsn.sexp import parse
-from freeroute.geometry import IntBox, IntPoint
+from freeroute.geometry import IntBox, IntPoint, Polyline, PolylineShape
 from freeroute.route import route, route_dsn_board_exact, route_dsn_board_rooms
 from freeroute.route.pipeline import _rule_clearance_dsn
 
+
+def _emitted_drc_violations(result, clearance):
+    """Independent DRC over the *emitted* route: reconstruct every wire's copper
+    tiles and return the different-net, same-layer pairs that come closer than
+    ``clearance``. This does NOT consult the search tree, so it catches copper
+    that is present in the output but (via a bug) absent from the tree -- exactly
+    the failure mode the wire/owner desync produced."""
+    items = []  # (net_no, layer, tile)
+    for net_no, segments in result.wires.items():
+        for layer, corners in segments:
+            for box in PolylineShape(Polyline(corners), result.half_width).tiles():
+                items.append((net_no, layer, box))
+    bad = []
+    for i in range(len(items)):
+        n1, l1, b1 = items[i]
+        expanded = b1.offset(clearance)
+        for j in range(i + 1, len(items)):
+            n2, l2, b2 = items[j]
+            if n1 == n2 or l1 != l2:
+                continue
+            if b2.overlaps(expanded):
+                bad.append((n1, n2))
+    return bad
+
+
 sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
 
 FIXTURES = Path(__file__).resolve().parent.parent / "dsn" / "fixtures"
@@ -37,6 +65,8 @@ KICAD = FIXTURES / "kicad_routable.dsn"
 NARROW = FIXTURES / "narrow_channel.dsn"
 SHOVE_CHANNEL = FIXTURES / "rooms_shove_channel.dsn"
 WIDE_DOOR = FIXTURES / "rooms_wide_door.dsn"
+MULTIPIN_DESYNC = FIXTURES / "rooms_multipin_desync.dsn"
+MULTIPIN_DESYNC_CRASH = FIXTURES / "rooms_multipin_desync_crash.dsn"
 
 FOUNDATION = [SIMPLE, CROSSING, KICAD, NARROW]
 
@@ -61,15 +91,15 @@ def _pins_by_net(fixture):
     return out
 
 
-# --- the headline density win -----------------------------------------------
+# --- shove recovers a greedy-ordering drop ----------------------------------
 
 
-def test_room_shove_channel_density_win():
+def test_room_shove_channel_recovers_greedy_ordering_drop():
     dsn = parse_dsn(SHOVE_CHANNEL.read_text())
     off, _, _ = route_dsn_board_rooms(dsn, shove=False)
     on, scale, _ = route_dsn_board_rooms(dsn, shove=True)
 
-    # without shove NET_A's sealed wall leaves no top<->bottom door -> NET_C drops
+    # under the default greedy net order NET_A (net 1) walls the channel -> NET_C drops
     assert off.routed_net_numbers == {1}
     assert off.drc_clean
     # with shove NET_A is nudged aside and both nets fit through the same channel
@@ -79,6 +109,42 @@ def test_room_shove_channel_density_win():
     assert on.tree.has_violation(_clearance(dsn, scale)) is None
 
 
+def test_room_shove_channel_drop_is_ordering_artifact_not_density():
+    """Honest bound on the shove_channel claim: the plain drop is an artifact of
+    the greedy net order, not a genuine density limit. The identical plain engine
+    routes BOTH nets with zero shoves if NET_C is listed first, or if the two
+    cosmetic edge seals are removed -- so shove here recovers a self-inflicted
+    ordering drop rather than overcoming an unroutable density. (The genuine
+    sub-cell win is occupancy packing, exercised by the wide_door fixture with
+    shoves == 0.)"""
+    orig = SHOVE_CHANNEL.read_text()
+
+    # (1) reorder so NET_C becomes net 1 -> plain routing solves it, no shove
+    swapped = orig.replace(
+        "    (net NET_A\n      (pins A1-1 A2-1)\n    )\n"
+        "    (net NET_C\n      (pins C1-1 C2-1)\n    )",
+        "    (net NET_C\n      (pins C1-1 C2-1)\n    )\n"
+        "    (net NET_A\n      (pins A1-1 A2-1)\n    )",
+    )
+    assert swapped != orig
+    reordered, _, _ = route_dsn_board_rooms(parse_dsn(swapped), shove=False)
+    assert reordered.routed_net_numbers == {1, 2}
+    assert reordered.shoves == 0
+    assert reordered.drc_clean
+
+    # (2) drop the seal keepouts -> plain routing solves it, no shove
+    noseal = orig.replace(
+        '    (keepout "seal_left"\n      (rect F.Cu 0 -30000 2500 0)\n    )\n'
+        '    (keepout "seal_right"\n      (rect F.Cu 197500 -30000 200000 0)\n    )\n',
+        "",
+    )
+    assert noseal != orig
+    unsealed, _, _ = route_dsn_board_rooms(parse_dsn(noseal), shove=False)
+    assert unsealed.routed_net_numbers == {1, 2}
+    assert unsealed.shoves == 0
+    assert unsealed.drc_clean
+
+
 def test_room_shove_channel_moves_blocker_but_keeps_its_pads():
     on, _, _ = route_dsn_board_rooms(parse_dsn(SHOVE_CHANNEL.read_text()), shove=True)
     pins = _pins_by_net(SHOVE_CHANNEL)
@@ -226,3 +292,57 @@ def test_free_intervals_splits_around_forbidden_band():
     assert _best_free_point(0, 200, [(87, 113)], ideal=100) == 87
     # no forbidden band -> the whole span, clamped to the ideal (old clamp)
     assert _best_free_point(0, 200, [], ideal=100) == 100
+
+
+# --- regression: multi-pin wire/owner desync in shove recovery ---------------
+
+
+def test_room_shove_multipin_recovery_keeps_output_drc_clean():
+    """Regression for the wire/owner desync in ``_shove_recover_room``.
+
+    A 3-pin net commits one connection via ``_commit`` and has a second straight
+    connection *recovered* by the shove path. The recovery used to clobber the
+    net's ``_Accepted`` with a fresh one whose ``wire_owners`` held only the
+    just-recovered wire, leaving it SHORTER than the parallel ``wires`` list. A
+    later net's shove then removed the WRONG wire's copper from the search tree;
+    that copper stayed in the emitted route but vanished from the tree, so
+    ``has_violation`` falsely certified clean while a following net was placed on
+    top of it -- a hard different-net short in the SES.
+
+    Assert the invariant against the *emitted* output directly, not just the tree
+    (the tree was the thing being fooled)."""
+    dsn = parse_dsn(MULTIPIN_DESYNC.read_text())
+    on, scale, _ = route_dsn_board_rooms(dsn, shove=True)
+    clearance = _clearance(dsn, scale)
+
+    # the tree self-check and the independent emitted-copper check must agree
+    assert on.drc_clean
+    assert on.tree.has_violation(clearance) is None
+    assert _emitted_drc_violations(on.result, clearance) == []
+    # the shove path actually engaged and did not silently drop the multi-pin net
+    assert on.shoves >= 1
+    assert 3 in on.routed_net_numbers
+
+
+def test_room_shove_multipin_recovery_is_deterministic():
+    a, _, _ = route_dsn_board_rooms(parse_dsn(MULTIPIN_DESYNC.read_text()), shove=True)
+    b, _, _ = route_dsn_board_rooms(parse_dsn(MULTIPIN_DESYNC.read_text()), shove=True)
+    assert _wire_key(a.result) == _wire_key(b.result)
+    assert a.routed_net_numbers == b.routed_net_numbers
+
+
+def test_room_shove_multipin_recovery_does_not_crash():
+    """Sibling of the desync: when the conflicting wire index exceeds the
+    (formerly truncated) ``wire_owners`` length, the recovery raised
+    ``IndexError`` and aborted the whole public route. Keeping ``wire_owners``
+    parallel to ``wires`` fixes both faces; this board must route to completion,
+    DRC-clean, through the public ``route(engine="room", shove=True)`` API."""
+    ses = route(MULTIPIN_DESYNC_CRASH.read_text(), engine="room", shove=True)
+    top = parse(ses)
+    assert top.head == "session"
+    # and the library path stays DRC-clean on the emitted output
+    dsn = parse_dsn(MULTIPIN_DESYNC_CRASH.read_text())
+    on, scale, _ = route_dsn_board_rooms(dsn, shove=True)
+    clearance = _clearance(dsn, scale)
+    assert on.drc_clean
+    assert _emitted_drc_violations(on.result, clearance) == []