Standard CRX over-approximates when Hasse diagram is non-linear (24% of
RAGSAK packages). Cluster-then-infer groups sequences by (first, last,
length), infers per-cluster, picks largest cluster's grammar.
Results on RAGSAK:
Avg max disjunction: 2.8 → 1.7 (39% tighter)
Packages improved: 6/10
Tradeoff: cluster granularity (too coarse = over-approximation,
too fine = no generalization). Current: (first, last, length_bucket).
Exports crx_refined() and crx_with_confidence() from bex package.
20 new tests. All 199 tests pass.
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