Add true_density.dsn: NET_C is a full-height wall on the sole signal layer,
so plain room routing drops a net under every net ordering (an order-independent
obstruction, verified over all permutations), unlike rooms_shove_channel whose
plain drop fits under a reorder.
Test that shove recovers nothing on this board (shoves == 0, same routed set as
plain) while staying DRC-clean, and that the only difference from the recoverable
shove_channel is the wall's span. shove relocates a blocker into existing free
space; where the wall leaves no headroom there is nowhere to relocate to, so it
cannot manufacture density. The recover/fail boundary is the free-space boundary.
_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.
rooms_shove_channel is the headline density win: a sealed NET_A wall
leaves no top<->bottom door, so plain room routing drops NET_C; with
shove=True NET_A is nudged aside and both nets route, DRC-clean and
deterministic. rooms_wide_door seats two nets through one wide gap at
distinct projected gate points with no shove.
Cover the occupancy-aware projection math directly, assert the four
foundation fixtures stay byte-identical under shove=True (shoves==0), and
extend the room DRC-clean parametrize with both new fixtures.
