Conformance: SimpleDateFormat parse + read over host readers

- java.text.SimpleDateFormat.parse parses the RFC1123/1036/asctime patterns
  (day/month names, 2-digit-year sliding window, tz token), and .format renders
  z/Z/X timezone tokens (GMT/+0000/Z) instead of emitting them literally. Date
  gains toLocalDate/toLocalDateTime/before/after/equals. Fixes ring.util.time.
- read / read+string work over a host java.io reader (StringReader wrapped in a
  PushbackReader): drain, parse one form, push the tail back. Fixes cuerdas
  istr / << string interpolation (and selmer's <<), which read embedded forms
  from the template via (read pushback-reader).

host/chez/post-prelude.ss

@@ -101,3 +101,40 @@
 ;; :jolt/deftype)) — the get-trick invokes a sorted-map's comparator on
 ;; :jolt/deftype and throws (jolt-3bbj). Matches the JVM (instance? IRecord).
 (def-var! "clojure.core" "record?" (lambda (x) (jrec? x)))
+
+;; read / read+string over a HOST reader jhost (java.io StringReader/PushbackReader):
+;; the overlay's IReader protocol only covers the reify map-reader, so a (read
+;; pushback-reader) — cuerdas' string interpolation — would miss. Intercept a host
+;; reader; everything else (the *in* reify) delegates to the overlay.
+(let ((ov-read (var-deref "clojure.core" "read")))
+  (def-var! "clojure.core" "read"
+    (case-lambda
+      (() (jolt-invoke ov-read))
+      ((stream)
+       (if (reader-jhost? stream)
+           (let-values (((form found?) (host-reader-read-form stream)))
+             (if found? form (jolt-throw (jolt-ex-info "EOF while reading" (empty-pmap)))))
+           (jolt-invoke ov-read stream)))
+      ((stream e? ev)
+       (if (reader-jhost? stream)
+           (let-values (((form found?) (host-reader-read-form stream)))
+             (cond (found? form)
+                   ((jolt-truthy? e?) (jolt-throw (jolt-ex-info "EOF while reading" (empty-pmap))))
+                   (else ev)))
+           (jolt-invoke ov-read stream e? ev))))))
+(let ((ov-rps (var-deref "clojure.core" "read+string")))
+  (def-var! "clojure.core" "read+string"
+    (case-lambda
+      (() (jolt-invoke ov-rps))
+      ((stream) (jolt-invoke (var-deref "clojure.core" "read+string") stream #t jolt-nil))
+      ((stream e? ev)
+       (if (reader-jhost? stream)
+           (let* ((s (drain-reader stream)) (pr (jolt-parse-next s)))
+             (if (jolt-nil? pr)
+                 (begin (reader-refill! stream "")
+                        (if (jolt-truthy? e?) (jolt-throw (jolt-ex-info "EOF while reading" (empty-pmap)))
+                            (jolt-vector ev "")))
+                 (let ((rest (jolt-nth pr 1)))
+                   (reader-refill! stream rest)
+                   (jolt-vector (jolt-nth pr 0) (substring s 0 (- (string-length s) (string-length rest)))))))
+           (jolt-invoke ov-rps stream e? ev))))))