Contract fixes from the baseline audit; every residual suite failure traced

Auditing the remaining cts baseline for R7 exposed real contract gaps hiding
among the model residue — all fixed to reference behavior:

- stale no-ratio-era stubs: numerator/denominator now work over jolt's exact
  rationals (non-ratio is the Ratio cast failure); rational? includes decimals
- casts and pending: peek/pop demand an IPersistentStack (pop nil is nil),
  realized? demands an IPending (a plain list/range throws), transient demands
  an editable COLLECTION (non-colls throw; the RFC 0003 sorted/list/seq
  superset keeps the copy-on-write fallback), empty on a plain record throws
- nil and empties: (nth nil i) is nil, (nth nil i d) is d, a nil index is NPE,
  keys/vals of anything empty are nil, (conj nil) is nil
- lookups: contains? on a string is index-only (other keys IAE), get on an
  array is lenient (nth still throws), a VECTOR invocation has nth semantics
  (([1 2] 5) throws — call position and jolt-invoke both)
- into only transients editable collections; a PersistentQueue/sorted target
  folds through conj (RT's IEditableCollection split)
- numbers: number?/num accept BigDecimal, quot/rem throw on an Infinite/NaN
  quotient, even?/odd? demand integers
- ordering: keywords compare namespace-first with nil first (Symbol.compareTo)
- misc: run! honors reduced, eval self-evaluates non-form values, intern
  demands an existing namespace, counted? excludes strings, seqable? includes
  arrays, shuffle rejects maps, sort-by rejects a collection comparator,
  when-let demands one binding pair, case*/deftype*/letfn*/reify*/& are
  special symbols

Two mis-certified corpus rows fixed (they threw on the JVM too and hid in the
tolerated bucket): a raw \d string escape and duplicate literal map keys.

SPEC.md gains the baseline-traceability section: every one of the 146
remaining suite failures maps to a documented divergence (integer-box,
no-single-float, RFC 0003 transients, seq/chunking model, stm-refs,
parse-uuid strictness, vec-array adoption). cts baseline 5955 -> 6042 pass,
5 errors, 30 namespaces. 9 JVM-certified corpus rows.

jolt-core/clojure/core/22-coll.clj

@@ -136,6 +136,9 @@
     ;; a deftype/record with its own empty (IPersistentCollection) — e.g.
     ;; data.priority-map — uses it, before the generic map/set/vector arms.
     (jolt.host/jrec-method? coll "empty") (.empty coll)
+    ;; a defrecord without its own empty can't have one (RT: UnsupportedOperation)
+    (record? coll) (throw (new UnsupportedOperationException
+                               (str "Can't create empty: " (.getName (class coll)))))
     (sorted? coll) ((get (jolt.host/ref-get coll :ops) :empty) coll)
     (map? coll) (with-meta {} (meta coll))
     (set? coll) (with-meta #{} (meta coll))
@@ -330,7 +333,8 @@
 ;; stays an unevaluated reader form on jolt and contains? can't see into it.
 (def ^:private special-syms
   #{'if 'do 'let* 'fn* 'quote 'var 'def 'loop* 'recur 'throw 'try 'catch
-    'finally 'new 'set! '. 'monitor-enter 'monitor-exit})
+    'finally 'new 'set! '. 'monitor-enter 'monitor-exit
+    '& 'case* 'deftype* 'letfn* 'reify*})
 
 (defn special-symbol? [s] (contains? special-syms s))