assign_solver="cpsat" gave a different leaf-type signature on every run
from an identical seed, in the same process. One line:
assignable = scope if scope is not None else set(leaves)
noncirc = [L for L in assignable if L not in circ] # id() order
assignable is a set of dom.Node, and Node hashes by id() -- a memory
address -- so iterating it ordered noncirc, and hence room_slots, by where
the objects happened to land in memory. That shifts between calls within
one process as allocation patterns change, with no seed involved.
Only cpsat showed it. The greedy path re-sorts every slot list with -idx[L]
as a unique tiebreak and is immune to the incoming order; CP-SAT consumes
room_slots order as its model's variable order, and the labelling problem
has many equally-optimal solutions. Greedy was not more correct, it was
masking a defect that had been there all along.
Fix: iterate the tree-ordered list, use the set only for membership.
Verified on programme-house, harbor-house and maple-court: 1 distinct
signature over 5 runs on both solvers, and 1 across 4 processes started
with different PYTHONHASHSEED, so context_types' string sets are not a
second source. test_constructive_topology_is_bit_reproducible guards both.
Method: rather than guess which set was at fault, instrument
solve_room_labels with an id-free fingerprint of inputs and outputs and
isolate the FIRST call, since later calls legitimately depend on earlier
ones through leaf types. Five runs gave five distinct first-call inputs,
placing the fault upstream of the solver in one step.
Every A/B on the cpsat path was comparing arms that differed partly by
memory layout -- 39.5's cpsat-vs-greedy verdict included, already down for
re-measurement under homemaker-py-vjd. Same id()-keying hazard as the
documented geometry._cache issue and a plausible contributor to
homemaker-py-b8g, which stays open: n_workers>1 has its own BLAS mechanism
and is not addressed here.
Closes homemaker-py-fdp.
Lint at parity (46); tests 381 passed (2 new), 0 failed.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MJ84Feep79Hhm3E4zZJmnB
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