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.

test/conformance/SPEC.md

@@ -205,3 +205,40 @@ corpus`.
   deliberate delta (classify it in `known-divergences.edn`).
 - **Refresh the profile**: re-run with `--profile test/conformance/profile.edn`.
 - **Re-floor the runtime gate** when parity rises (`host/chez/run-corpus.ss`).
+
+## clojure-test-suite baseline traceability
+
+Every residual entry in `test/chez/cts-known-failures.txt` traces to one
+documented model divergence — nothing in the baseline is an unexplained bug:
+
+- `:integer-box-model` (this file, above): every `big-int?`/`instance?
+  Byte…BigInt` class check, the overflow-throw rows (`(+ max-long 1)` is a
+  bignum, not ArithmeticException — abs/inc/dec/minus/plus/star/quot/rem/mod/
+  bit-set and the `+'`/`*'` promotion-identity namespaces), boxed-identity
+  rows (`(identical? (Boolean. "true") true)`, `(= x x)` on a boxed NaN — jolt
+  numbers are immediates, there is no box to distinguish), and `num`'s
+  primitive-overload reflection rows.
+- **no single float** (Narrow integer types, above): `(float Double/MIN_VALUE)`
+  keeps the double value instead of rounding to 0.0f; `(double? (float x))`
+  is true.
+- **RFC 0003 transients**: `(transient sorted/list/lazy-seq)` succeeds through
+  the copy-on-write fallback (a deliberate superset; non-collections now throw
+  like the JVM), and double-transient is idempotent rather than throwing.
+- `:seq-type-model`/`:chunking-model` (Seq semantics, above): `realized?` on
+  the rest of a realized chain (a plain seq cell on jolt, a cached LazySeq on
+  the JVM), `p/lazy-seq?` on forced rest chains, and chunk-granularity
+  realization counts (lazy-seq namespace).
+- **stm-refs** (`coverage.md`): the `(ref …)`/`dosync` sections of the watch
+  namespaces (add-watch/remove-watch) — refs are out of scope pending the
+  concurrency design note.
+- **parse-uuid strictness** (spec §9, parse-uuid S3): jolt is deliberately
+  strict where the reference's java.util.UUID accepts non-canonical forms
+  like `"0-0-0-0-0"`.
+- **vec of an array copies**: the reference ADOPTS an Object array (mutating
+  the array mutates the vector); jolt copies — immutable semantics win over
+  the implementation leak (`vec` namespace, one row).
+- **eval of JVM shapes** (`rand-nth`/`eval` residue): rows needing JVM-only
+  evaluation shapes (e.g. evaluating a Java array literal).
+
+A future change that makes any of these rows pass will fail the cts gate as
+STALE, forcing this section and the baseline to be updated together.