diff --git a/host/chez/host-static-classes.ss b/host/chez/host-static-classes.ss
index deb5d40..59a2b02 100644
--- a/host/chez/host-static-classes.ss
+++ b/host/chez/host-static-classes.ss
@@ -73,12 +73,19 @@
     (cons "iterator" (lambda (self) (make-jiterator (list->cseq (al->list self)))))
     (cons "toString" (lambda (self) (jolt-pr-str (list->cseq (al->list self)))))))
 
+;; Appendable.append text: append(x) renders x; append(csq,start,end) appends the
+;; subsequence csq[start,end) (data.json's writer appends string runs this way).
+(define (append-text x rest)
+  (if (null? rest)
+      (render-piece x)
+      (substring (render-piece x) (jnum->exact (car rest)) (jnum->exact (cadr rest)))))
+
 (register-class-ctor! "StringBuilder"
   (lambda args (make-jhost "string-builder"
     ;; a numeric first arg is a CAPACITY hint, not content.
     (vector (if (and (pair? args) (not (number? (car args)))) (render-piece (car args)) "")))))
 (register-host-methods! "string-builder"
-  (list (cons "append" (lambda (self x) (sb-set! self (string-append (sb-str self) (render-piece x))) self))
+  (list (cons "append" (lambda (self x . rest) (sb-set! self (string-append (sb-str self) (append-text x rest))) self))
         (cons "toString" (lambda (self) (sb-str self)))
         (cons "length" (lambda (self) (->num (string-length (sb-str self)))))
         (cons "charAt" (lambda (self i) (string-ref (sb-str self) (jnum->exact i))))
@@ -88,6 +95,9 @@
                                                 (substring cur 0 n)
                                                 (string-append cur (make-string (- n (string-length cur)) #\nul)))))
                             jolt-nil))))
+;; (str sb) / print a StringBuilder -> its accumulated content, like the JVM
+;; (str calls toString). Without this str renders the opaque host object.
+(register-str-render! (lambda (x) (and (jhost? x) (string=? (jhost-tag x) "string-builder"))) sb-str)
 
 ;; ---- StringWriter -----------------------------------------------------------
 ;; Writer.write(int) writes the CHAR for that code; append(char) appends the char.
@@ -95,7 +105,7 @@
 (register-class-ctor! "StringWriter" (lambda args (make-jhost "writer" (vector ""))))
 (register-host-methods! "writer"
   (list (cons "write" (lambda (self x) (sb-set! self (string-append (sb-str self) (writer-piece x))) jolt-nil))
-        (cons "append" (lambda (self x) (sb-set! self (string-append (sb-str self) (render-piece x))) self))
+        (cons "append" (lambda (self x . rest) (sb-set! self (string-append (sb-str self) (append-text x rest))) self))
         (cons "flush" (lambda (self) jolt-nil))
         (cons "close" (lambda (self) jolt-nil))
         (cons "toString" (lambda (self) (sb-str self)))))
@@ -109,7 +119,7 @@
 (define (fw-flush! self) (jolt-spit (fw-path self) (fw-buf self)))  ; jolt-spit: io.ss
 (register-host-methods! "file-writer"
   (list (cons "write" (lambda (self x) (fw-append! self (writer-piece x)) jolt-nil))
-        (cons "append" (lambda (self x) (fw-append! self (render-piece x)) self))
+        (cons "append" (lambda (self x . rest) (fw-append! self (append-text x rest)) self))
         (cons "flush" (lambda (self) (fw-flush! self) jolt-nil))
         (cons "close" (lambda (self) (fw-flush! self) jolt-nil))
         (cons "toString" (lambda (self) (fw-buf self)))))
@@ -120,7 +130,7 @@
 ;; (tools.logging, selmer) compile and run.
 (register-host-methods! "port-writer"
   (list (cons "write" (lambda (self x) (display (writer-piece x) (vector-ref (jhost-state self) 0)) jolt-nil))
-        (cons "append" (lambda (self x) (display (render-piece x) (vector-ref (jhost-state self) 0)) self))
+        (cons "append" (lambda (self x . rest) (display (append-text x rest) (vector-ref (jhost-state self) 0)) self))
         (cons "flush" (lambda (self) (flush-output-port (vector-ref (jhost-state self) 0)) jolt-nil))
         (cons "close" (lambda (self) jolt-nil))
         (cons "toString" (lambda (self) ""))))
@@ -291,6 +301,15 @@
   (lambda (x . rest)
     (cond ((bytevector? x) (decode-bytevector x rest))
           ((and (jolt-array? x) (eq? (jolt-array-kind x) 'byte)) (decode-bytevector (na-bytearray->bv x) rest))
+          ;; (String. char[] [offset count]) — the whole array or a slice. Buffered
+          ;; readers (data.json) build a string from a fill buffer this way.
+          ((and (jolt-array? x) (eq? (jolt-array-kind x) 'char))
+           (let ((v (jolt-array-vec x)))
+             (if (pair? rest)
+                 (let* ((off (jnum->exact (car rest))) (cnt (jnum->exact (cadr rest))) (out (make-string cnt)))
+                   (let loop ((i 0)) (when (fx<? i cnt) (string-set! out i (vector-ref v (fx+ off i))) (loop (fx+ i 1))))
+                   out)
+                 (list->string (vector->list v)))))
           ((string? x) x)
           (else (jolt-str-render-one x)))))
 (register-class-ctor! "BigInteger"
diff --git a/host/chez/inst-time.ss b/host/chez/inst-time.ss
index c71fa69..e32e4c2 100644
--- a/host/chez/inst-time.ss
+++ b/host/chez/inst-time.ss
@@ -356,8 +356,11 @@
 ;; java.util.TimeZone: an opaque id holder (format-ms is UTC, so a non-UTC zone is
 ;; not honored — only the UTC case the corpus uses is exercised).
 (define (timezone-of id) (make-jhost "timezone" (vector (if (string? id) id (jolt-str-render-one id)))))
-(register-class-statics! "TimeZone" (list (cons "getTimeZone" timezone-of)))
-(register-class-statics! "java.util.TimeZone" (list (cons "getTimeZone" timezone-of)))
+(define timezone-statics
+  (list (cons "getTimeZone" timezone-of)
+        (cons "getDefault" (lambda () (timezone-of "default")))))
+(register-class-statics! "TimeZone" timezone-statics)
+(register-class-statics! "java.util.TimeZone" timezone-statics)
 
 ;; java.text.SimpleDateFormat: holds a pattern; .setTimeZone is accepted (format-ms
 ;; is UTC); .format(date) renders the date per the pattern via the format-ms engine.
diff --git a/host/chez/natives-str.ss b/host/chez/natives-str.ss
index 58f182f..3bb1614 100644
--- a/host/chez/natives-str.ss
+++ b/host/chez/natives-str.ss
@@ -166,6 +166,18 @@
     ((or (string=? method "getName") (string=? method "getCanonicalName")) s)
     ((string=? method "getSimpleName")
      (let ((i (str-last-index-of s "."))) (if (>= i 0) (substring s (+ i 1) (string-length s)) s)))
+    ;; .getChars srcBegin srcEnd dst dstBegin — copy s[srcBegin,srcEnd) into the
+    ;; char-array dst at dstBegin (used by buffered readers, e.g. data.json).
+    ((string=? method "getChars")
+     (let ((src-begin (jolt->idx (arg 0))) (src-end (jolt->idx (arg 1)))
+           (dv (jolt-array-vec (arg 2))) (dst-begin (jolt->idx (arg 3))))
+       (let loop ((i src-begin) (j dst-begin))
+         (when (fx<? i src-end)
+           (vector-set! dv j (string-ref s i))
+           (loop (fx+ i 1) (fx+ j 1)))))
+     jolt-nil)
+    ((string=? method "subSequence")
+     (substring s (jolt->idx (arg 0)) (jolt->idx (arg 1))))
     (else (error #f (string-append "No method " method " for value")))))
 
 ;; --- clojure.core str-* primitives (the substrate clojure.string.clj calls) ---
diff --git a/host/chez/reader.ss b/host/chez/reader.ss
index 8fdc579..4c58522 100644
--- a/host/chez/reader.ss
+++ b/host/chez/reader.ss
@@ -177,7 +177,21 @@
              ((#\0) (loop (+ i 2) (cons #\nul acc)))
              ((#\u)
               (let-values (((cp j) (rdr-hex->int s (+ i 2) 4)))
-                (loop j (cons (integer->char cp) acc))))
+                ;; A \u escape is a UTF-16 code unit. jolt chars are Unicode scalars,
+                ;; so combine a high+low surrogate pair (😃 -> U+1F603) into
+                ;; the one scalar char. A lone surrogate has no scalar — emit U+FFFD
+                ;; rather than crash (the irreducible UTF-16/scalar divergence).
+                (cond
+                  ((and (fx>=? cp #xD800) (fx<=? cp #xDBFF)
+                        (fx<? (fx+ j 1) end)
+                        (char=? (string-ref s j) #\\) (char=? (string-ref s (fx+ j 1)) #\u))
+                   (let-values (((lo k) (rdr-hex->int s (+ j 2) 4)))
+                     (if (and (fx>=? lo #xDC00) (fx<=? lo #xDFFF))
+                         (loop k (cons (integer->char
+                                        (fx+ #x10000 (fx* (fx- cp #xD800) 1024) (fx- lo #xDC00))) acc))
+                         (loop j (cons #\xFFFD acc)))))
+                  ((and (fx>=? cp #xD800) (fx<=? cp #xDFFF)) (loop j (cons #\xFFFD acc)))
+                  (else (loop j (cons (integer->char cp) acc))))))
              (else (loop (+ i 2) (cons e acc))))))
         (else (loop (+ i 1) (cons c acc)))))))
 
diff --git a/test/chez/corpus.edn b/test/chez/corpus.edn
index e476c58..39337fa 100644
--- a/test/chez/corpus.edn
+++ b/test/chez/corpus.edn
@@ -2981,4 +2981,8 @@
   {:suite "interop / instance? on host interfaces" :label "map is not a Collection" :expected "false" :actual "(instance? java.util.Collection {:a 1})"}
   {:suite "interop / instance? on host interfaces" :label "vector is Associative" :expected "true" :actual "(instance? clojure.lang.Associative [1])"}
   {:suite "interop / instance? on host interfaces" :label "string is not Number" :expected "false" :actual "(instance? java.lang.Number \"s\")"}
+  {:suite "interop / String & StringBuilder char ops" :label "String from char-array slice" :expected "\"abc\"" :actual "(String. (char-array [\\a \\b \\c \\d]) 0 3)"}
+  {:suite "interop / String & StringBuilder char ops" :label "str of StringBuilder" :expected "\"hi\"" :actual "(let [sb (StringBuilder.)] (.append sb \"hi\") (str sb))"}
+  {:suite "interop / String & StringBuilder char ops" :label "append subsequence" :expected "\"bcd\"" :actual "(let [sb (StringBuilder.)] (.append sb \"abcde\" 1 4) (.toString sb))"}
+  {:suite "interop / String & StringBuilder char ops" :label "String.getChars into buffer" :expected "\"abc\"" :actual "(let [a (char-array 4)] (.getChars \"abcd\" 0 3 a 0) (String. a 0 3))"}
 ]