Comb pass 2026-05-21 (item 4).
Pre-fix the topological-sort implementation in
``PropositionGraph.topo_order`` had two compounding inefficiencies:
* ``queue.pop(0)`` on a list is O(N) per pop → O(N²) total
* The inner ``for e in self.edges`` rescanned all edges on every
iteration → O(N × E) overall
This is invisible on today's 1–2 node production graphs but would
become a real regression the moment compound-intent multi-node
dispatch (ADR-0089 Phase C2) or the grounded realizer's multi-clause
output (ADR-0088 Phase B follow-up) lands.
Fix: standard Kahn's with a precomputed out-edge adjacency map and
a ``deque`` for the work queue. O(N + E) overall. Deterministic
output preserved — the queue is seeded with sorted zero-in-degree
nodes (identical to the pre-fix list sort), and direct-successor
order matches edge-iteration order (identical when edges retain
insertion order).
Pinned by 6 new tests in ``tests/test_graph_topo_order_perf.py``:
* single-node graph (today's production shape) byte-identical to
pre-fix output
* empty graph returns empty tuple
* chain (A→B→C→D) orders root → leaf
* diamond (A→B, A→C, B→D, C→D) keeps A first, D last, B/C between
* three disjoint roots emit in sorted order
* 100-node chain returns correct full order (would have been
visibly slow under the O(N²) pre-fix algorithm)
Validation:
* ``core eval cognition`` byte-identical (public 100/100/91.7/100)
* ``core test --suite cognition`` 120/0/1
* ``core test --suite smoke`` 67/0
Comb-pass note: item 15 (GenerationResult.tokens typed tuple but
assigned list) was investigated and turned out to be a Pyright
false positive — ``GenerationResult.__post_init__`` already coerces
to tuple via ``object.__setattr__``. Contract is enforced at
runtime; only Pyright's static analyser misses the coercion site.
No fix needed.
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