Class-name symbols self-evaluate; extends? matches host classes; ISO_INSTANT

A slash-free dotted symbol with a Capitalized final segment (java.util.Map,
clojure.lang.Named, java.time.Instant) now self-evaluates to its name string
instead of resolving to nil — jolt models a class as its name, so a library
can extend a protocol to, or instance?-check, a host class jolt has no shim
for. hc-resolve-global classifies these as :class; the analyzer emits a const.

extends? now matches when either the query or the registered tag is a dotted
suffix of the other, so (extends? P java.util.Collection) finds the impl
extend registered under the canonical short tag.

Add DateTimeFormatter/ISO_INSTANT (UTC, trailing Z).

These unblock loading clojure.data.json, which dispatches JSONWriter on
java.util.Map/Collection/CharSequence/Instant and defaults a formatter to
ISO_INSTANT.

host/chez/host-contract.ss

@@ -32,6 +32,7 @@
 (define hc-kw-name  (keyword #f "name"))
 (define hc-kw-var   (keyword #f "var"))
 (define hc-kw-unresolved (keyword #f "unresolved"))
+(define hc-kw-class (keyword #f "class"))
 (define hc-kw-num-ret (keyword #f "num-ret"))
 (define hc-kw-double (keyword #f "double"))
 (define hc-kw-long (keyword #f "long"))
@@ -192,6 +193,19 @@
                    ((equal? t "long") hc-kw-long)
                    (else #f))))))
 
+;; A slash-free dotted symbol whose final segment is Capitalized is a class
+;; reference (java.util.Map, clojure.lang.Named) — Clojure has no such vars. With
+;; no JVM classes, jolt models a class as its name string, so the symbol
+;; self-evaluates to that string (the analyzer emits a :const). This lets a lib
+;; extend a protocol to / instance?-check a host class jolt has no shim for.
+(define (hc-fq-class-name? nm)
+  (let ((n (string-length nm)))
+    (let loop ((i (fx- n 1)))
+      (cond ((fx<? i 0) #f)
+            ((char=? (string-ref nm i) #\.)
+             (and (fx<? (fx+ i 1) n) (char-upper-case? (string-ref nm (fx+ i 1)))))
+            (else (loop (fx- i 1)))))))
+
 (define (hc-resolve-global ctx sym)
   (let* ((nm (symbol-t-name sym))
          (cell (hc-resolve-cell ctx sym)))
@@ -201,7 +215,9 @@
                                    hc-kw-name (var-cell-name cell)))
               (nr (hc-cell-num-ret cell)))
           (if nr (jolt-assoc base hc-kw-num-ret nr) base))
-        (jolt-hash-map hc-kw-kind hc-kw-unresolved hc-kw-name nm))))
+        (if (hc-fq-class-name? nm)
+            (jolt-hash-map hc-kw-kind hc-kw-class hc-kw-name nm)
+            (jolt-hash-map hc-kw-kind hc-kw-unresolved hc-kw-name nm)))))
 
 (define (hc-intern! ctx ns-name nm) (declare-var! ns-name nm) jolt-nil)
 

host/chez/inst-time.ss

@@ -320,6 +320,8 @@
   (list (cons "ofPattern" (lambda (p . _) (mk-formatter p)))
         (cons "ISO_LOCAL_DATE" (mk-formatter "yyyy-MM-dd"))
         (cons "ISO_LOCAL_DATE_TIME" (mk-formatter "yyyy-MM-dd'T'HH:mm:ss"))
+        ;; ISO_INSTANT always renders in UTC with a trailing Z (format-ms is UTC; X -> "Z").
+        (cons "ISO_INSTANT" (mk-formatter "yyyy-MM-dd'T'HH:mm:ssX"))
         (cons "ofLocalizedDate" (lambda (fs) (style-fmt 'date fs)))
         (cons "ofLocalizedTime" (lambda (fs) (style-fmt 'time fs)))
         (cons "ofLocalizedDateTime" (lambda (fs) (style-fmt 'datetime fs)))))