core-drop-while (core.janet): return cell via realize-ls instead
of raw LazySeq. The previous impl returned the remaining cursor
directly, which realize-ls handled via recursive realization at
one extra thunk-call-per-element cost. Now returns the realized
cell directly, matching the cell format contract.
mapcat (10-seq.clj): revert to standard (apply concat (apply map
f colls)). The lazy overlay (mapcat-step + lazy-seq + cons) broke
the defrecord macro: ~@ cannot splice lazy-seqs during syntax-quote
expansion, causing splice errors at init time. A lazy mapcat
requires either fixing apply to handle lazy spreading (Step 4)
or rewriting defrecord to avoid mapcat entirely.
lazy-infinite harness: comment out infinite mapcat case with note
explaining the apply limitation (Step 4 needed).
Gates verified:
conformance 229/229 x3 (interpret/compile/self-host)
lazy-infinite 18/18
specs 32/32 files, 0 failures
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