Nine more seed leaves move to 20-coll.clj (verified leaf-by-leaf: defn +
core-bindings entry only, no internal callers). fnil is upgraded to Clojure's
canonical 2/3/4-arity — it patches only the first 1-3 arguments; the old
kernel fn patched every position it had a default for, which Clojure does
not. The rest carry their kernel semantics over unchanged (bigdec is a
double, numerator/denominator throw, supers is #{}, munge rewrites dashes).
16 new spec rows incl. the fnil arity-contract cases. Gate green:
conformance 326x3, suite 4577, full jpm test (2:18 — first full run with the
ctx image cache on main).
Add spec suites for conditionals/logic/let/loop/iteration/threading, functions
(definition, application, combinators), and destructuring across let/fn/loop/
doseq/for. Bug caught and fixed: loop* assumed simple-symbol bindings, so
(loop [[a b] [1 2]] ...) errored; it now destructures each binding via
destructure-bind, supporting patterns in loop bindings (and recur). jpm test green.
