diff --git a/lib/smalltalk/runtime.sx b/lib/smalltalk/runtime.sx
new file mode 100644
index 00000000..d89f3461
--- /dev/null
+++ b/lib/smalltalk/runtime.sx
@@ -0,0 +1,370 @@
+;; lib/smalltalk/runtime.sx — Smalltalk primitives on SX
+;;
+;; Provides Smalltalk-idiomatic wrappers over SX built-ins.
+;; Primitives used:
+;;   make-set/set-add!/set-member?/set-remove!/set->list  (Phase 18)
+;;   char->integer/integer->char/list->string             (Phase 5)
+;;   bitwise-and/or/xor/not/arithmetic-shift              (Phase 7)
+;;   gcd/lcm/quotient/remainder/modulo                    (Phase 15)
+
+;; ---------------------------------------------------------------------------
+;; 0. Internal list helpers (used by Array and Dictionary)
+;; ---------------------------------------------------------------------------
+
+(define
+  (st-list-set-nth lst i newval)
+  (letrec
+    ((go (fn (ps j) (if (= (len ps) 0) (list) (cons (if (= j i) newval (first ps)) (go (rest ps) (+ j 1)))))))
+    (go lst 0)))
+
+(define
+  (st-list-remove-nth lst i)
+  (letrec
+    ((go (fn (ps j) (if (= (len ps) 0) (list) (if (= j i) (go (rest ps) (+ j 1)) (cons (first ps) (go (rest ps) (+ j 1))))))))
+    (go lst 0)))
+
+;; ---------------------------------------------------------------------------
+;; 1. Numeric helpers
+;;    Thin wrappers or direct aliases for Smalltalk Number protocol.
+;; ---------------------------------------------------------------------------
+
+(define (st-abs x) (abs x))
+(define (st-max a b) (if (> a b) a b))
+(define (st-min a b) (if (< a b) a b))
+(define (st-gcd a b) (gcd a b))
+(define (st-lcm a b) (lcm a b))
+(define (st-quo a b) (quotient a b))
+(define (st-rem a b) (remainder a b))
+(define (st-mod a b) (modulo a b))
+(define (st-even? n) (= (remainder n 2) 0))
+(define (st-odd? n) (not (st-even? n)))
+(define (st-sqrt x) (sqrt x))
+(define (st-floor x) (floor x))
+(define (st-ceiling x) (ceil x))
+(define (st-truncated x) (truncate x))
+(define (st-rounded x) (round x))
+
+;; ---------------------------------------------------------------------------
+;; 2. Character
+;;    Smalltalk $A = char 65. Operations mirror Character class.
+;; ---------------------------------------------------------------------------
+
+(define (st-char-value c) (char->integer c))
+(define (st-char-from-int n) (integer->char n))
+(define (st-char? v) (= (type-of v) "char"))
+
+(define
+  (st-char-is-letter? c)
+  (let
+    ((n (char->integer c)))
+    (or
+      (and (>= n 65) (<= n 90))
+      (and (>= n 97) (<= n 122)))))
+
+(define
+  (st-char-is-digit? c)
+  (let ((n (char->integer c))) (and (>= n 48) (<= n 57))))
+
+(define
+  (st-char-is-uppercase? c)
+  (let ((n (char->integer c))) (and (>= n 65) (<= n 90))))
+
+(define
+  (st-char-is-lowercase? c)
+  (let ((n (char->integer c))) (and (>= n 97) (<= n 122))))
+
+(define
+  (st-char-is-separator? c)
+  (let
+    ((n (char->integer c)))
+    (or
+      (= n 32)
+      (= n 9)
+      (= n 10)
+      (= n 13))))
+
+(define
+  (st-char-as-uppercase c)
+  (let
+    ((n (char->integer c)))
+    (if
+      (and (>= n 97) (<= n 122))
+      (integer->char (- n 32))
+      c)))
+
+(define
+  (st-char-as-lowercase c)
+  (let
+    ((n (char->integer c)))
+    (if
+      (and (>= n 65) (<= n 90))
+      (integer->char (+ n 32))
+      c)))
+
+(define (st-char-digit-value c) (- (char->integer c) 48))
+
+;; ---------------------------------------------------------------------------
+;; 3. Array (1-indexed, mutable, fixed-size)
+;;    Backed as {:__st_array__ true :size N "1" v1 "2" v2 ...}
+;;    Unset elements read as nil.
+;; ---------------------------------------------------------------------------
+
+(define
+  (st-array-new n)
+  (let
+    ((a (dict)))
+    (dict-set! a "__st_array__" true)
+    (dict-set! a "size" n)
+    a))
+
+(define (st-array? v) (and (dict? v) (dict-has? v "__st_array__")))
+
+(define (st-array-size a) (get a "size"))
+
+(define
+  (st-array-at a i)
+  (let ((v (get a (str i)))) (if (= v nil) nil v)))
+
+(define (st-array-at-put! a i v) (dict-set! a (str i) v) a)
+
+(define
+  (st-array-do a fn)
+  (letrec
+    ((go (fn (i) (when (<= i (st-array-size a)) (fn (st-array-at a i)) (go (+ i 1))))))
+    (go 1)))
+
+(define
+  (st-array->list a)
+  (letrec
+    ((go (fn (i acc) (if (< i 1) acc (go (- i 1) (cons (st-array-at a i) acc))))))
+    (go (st-array-size a) (list))))
+
+(define
+  (st-list->array xs)
+  (let
+    ((a (st-array-new (len xs))))
+    (letrec
+      ((go (fn (ys i) (when (> (len ys) 0) (st-array-at-put! a i (first ys)) (go (rest ys) (+ i 1))))))
+      (go xs 1))
+    a))
+
+(define
+  (st-array-copy-from-to a start stop)
+  (let
+    ((result (st-array-new (- stop start -1))))
+    (letrec
+      ((go (fn (i j) (when (<= i stop) (st-array-at-put! result j (st-array-at a i)) (go (+ i 1) (+ j 1))))))
+      (go start 1))
+    result))
+
+;; ---------------------------------------------------------------------------
+;; 4. Dictionary (hash map with any key via linear scan)
+;;    {:__st_dict__ true :size N :_pairs ((key val) ...)}
+;; ---------------------------------------------------------------------------
+
+(define
+  (st-dict-new)
+  (let
+    ((d (dict)))
+    (dict-set! d "__st_dict__" true)
+    (dict-set! d "size" 0)
+    (dict-set! d "_pairs" (list))
+    d))
+
+(define (st-dict? v) (and (dict? v) (dict-has? v "__st_dict__")))
+
+(define (st-dict-size d) (get d "size"))
+
+(define
+  (st-dict-find-idx pairs k)
+  (letrec
+    ((go (fn (ps i) (cond ((= (len ps) 0) -1) ((= (first (first ps)) k) i) (else (go (rest ps) (+ i 1)))))))
+    (go pairs 0)))
+
+(define
+  (st-dict-at d k)
+  (letrec
+    ((go (fn (ps) (if (= (len ps) 0) nil (if (= (first (first ps)) k) (nth (first ps) 1) (go (rest ps)))))))
+    (go (get d "_pairs"))))
+
+(define
+  (st-dict-at-put! d k v)
+  (let
+    ((pairs (get d "_pairs")) (idx (st-dict-find-idx (get d "_pairs") k)))
+    (if
+      (= idx -1)
+      (begin
+        (dict-set! d "_pairs" (append pairs (list (list k v))))
+        (dict-set! d "size" (+ (get d "size") 1)))
+      (dict-set! d "_pairs" (st-list-set-nth pairs idx (list k v)))))
+  d)
+
+(define
+  (st-dict-includes-key? d k)
+  (not (= (st-dict-find-idx (get d "_pairs") k) -1)))
+
+(define
+  (st-dict-at-default d k def)
+  (if (st-dict-includes-key? d k) (st-dict-at d k) def))
+
+(define
+  (st-dict-remove-key! d k)
+  (let
+    ((idx (st-dict-find-idx (get d "_pairs") k)))
+    (when
+      (not (= idx -1))
+      (dict-set! d "_pairs" (st-list-remove-nth (get d "_pairs") idx))
+      (dict-set! d "size" (- (get d "size") 1))))
+  d)
+
+(define (st-dict-keys d) (map first (get d "_pairs")))
+(define
+  (st-dict-values d)
+  (map (fn (p) (nth p 1)) (get d "_pairs")))
+
+(define
+  (st-dict-do d fn)
+  (for-each (fn (p) (fn (nth p 1))) (get d "_pairs")))
+
+(define
+  (st-dict-do-associations d fn)
+  (for-each (fn (p) (fn (first p) (nth p 1))) (get d "_pairs")))
+
+;; ---------------------------------------------------------------------------
+;; 5. Set (uniqueness via SX make-set)
+;;    Note: set-member?/set-add!/set-remove! take (set item) order.
+;; ---------------------------------------------------------------------------
+
+(define
+  (st-set-new)
+  (let
+    ((s (dict)))
+    (dict-set! s "__st_set__" true)
+    (dict-set! s "size" 0)
+    (dict-set! s "_set" (make-set))
+    s))
+
+(define (st-set? v) (and (dict? v) (dict-has? v "__st_set__")))
+
+(define (st-set-size s) (get s "size"))
+
+(define
+  (st-set-add! s v)
+  (let
+    ((sx (get s "_set")))
+    (when
+      (not (set-member? sx v))
+      (set-add! sx v)
+      (dict-set! s "size" (+ (get s "size") 1))))
+  s)
+
+(define (st-set-includes? s v) (set-member? (get s "_set") v))
+
+(define
+  (st-set-remove! s v)
+  (let
+    ((sx (get s "_set")))
+    (when
+      (set-member? sx v)
+      (set-remove! sx v)
+      (dict-set! s "size" (- (get s "size") 1))))
+  s)
+
+(define (st-set->list s) (set->list (get s "_set")))
+
+(define (st-set-do s fn) (for-each fn (st-set->list s)))
+
+;; ---------------------------------------------------------------------------
+;; 6. String / Stream utilities
+;; ---------------------------------------------------------------------------
+
+;; Join list of strings with separator
+(define
+  (st-join-strings strs sep)
+  (if
+    (= (len strs) 0)
+    ""
+    (letrec
+      ((go (fn (ss acc) (if (= (len ss) 0) acc (go (rest ss) (str acc sep (first ss)))))))
+      (go (rest strs) (first strs)))))
+
+;; printString — Smalltalk textual representation
+(define
+  (st-print-string v)
+  (cond
+    ((= v nil) "nil")
+    ((= v true) "true")
+    ((= v false) "false")
+    ((= (type-of v) "number") (str v))
+    ((= (type-of v) "string") (str "'" v "'"))
+    ((= (type-of v) "symbol") (str "#" (str v)))
+    ((= (type-of v) "char") (str "$" (list->string (list v))))
+    ((= (type-of v) "list")
+      (str "(" (st-join-strings (map st-print-string v) " ") ")"))
+    ((st-array? v)
+      (str
+        "(#("
+        (st-join-strings (map st-print-string (st-array->list v)) " ")
+        "))"))
+    (else (str v))))
+
+;; WriteStream — accumulates strings/chars to a buffer
+(define
+  (st-write-stream-new)
+  (let
+    ((ws (dict)))
+    (dict-set! ws "__st_ws__" true)
+    (dict-set! ws "contents" "")
+    ws))
+
+(define (st-write-stream? v) (and (dict? v) (dict-has? v "__st_ws__")))
+
+(define
+  (st-write-stream-put-string! ws s)
+  (dict-set! ws "contents" (str (get ws "contents") s))
+  ws)
+
+(define
+  (st-write-stream-next-put! ws c)
+  (st-write-stream-put-string! ws (list->string (list c))))
+
+(define
+  (st-write-stream-print! ws v)
+  (st-write-stream-put-string! ws (st-print-string v)))
+
+(define (st-write-stream-contents ws) (get ws "contents"))
+
+;; ReadStream — reads characters from a string one at a time
+(define
+  (st-read-stream-new s)
+  (let
+    ((rs (dict)))
+    (dict-set! rs "__st_rs__" true)
+    (dict-set! rs "_chars" (string->list s))
+    (dict-set! rs "pos" 0)
+    rs))
+
+(define (st-read-stream? v) (and (dict? v) (dict-has? v "__st_rs__")))
+
+(define
+  (st-read-stream-at-end? rs)
+  (>= (get rs "pos") (len (get rs "_chars"))))
+
+(define
+  (st-read-stream-next rs)
+  (if
+    (st-read-stream-at-end? rs)
+    nil
+    (let
+      ((c (nth (get rs "_chars") (get rs "pos"))))
+      (dict-set! rs "pos" (+ (get rs "pos") 1))
+      c)))
+
+(define
+  (st-read-stream-peek rs)
+  (if
+    (st-read-stream-at-end? rs)
+    nil
+    (nth (get rs "_chars") (get rs "pos"))))
+
+(define (st-read-stream-source rs) (list->string (get rs "_chars")))
diff --git a/lib/smalltalk/test.sh b/lib/smalltalk/test.sh
new file mode 100755
index 00000000..07e8a7ab
--- /dev/null
+++ b/lib/smalltalk/test.sh
@@ -0,0 +1,71 @@
+#!/usr/bin/env bash
+# lib/smalltalk/test.sh — smoke-test the Smalltalk runtime layer.
+# Uses sx_server.exe epoch protocol.
+#
+# Usage:
+#   bash lib/smalltalk/test.sh
+#   bash lib/smalltalk/test.sh -v
+
+set -uo pipefail
+cd "$(git rev-parse --show-toplevel)"
+
+SX_SERVER="${SX_SERVER:-hosts/ocaml/_build/default/bin/sx_server.exe}"
+if [ ! -x "$SX_SERVER" ]; then
+  SX_SERVER="/root/rose-ash/hosts/ocaml/_build/default/bin/sx_server.exe"
+fi
+if [ ! -x "$SX_SERVER" ]; then
+  echo "ERROR: sx_server.exe not found. Run: cd hosts/ocaml && dune build"
+  exit 1
+fi
+
+VERBOSE="${1:-}"
+TMPFILE=$(mktemp); trap "rm -f $TMPFILE" EXIT
+
+cat > "$TMPFILE" << 'EPOCHS'
+(epoch 1)
+(load "spec/stdlib.sx")
+(load "lib/smalltalk/runtime.sx")
+(epoch 2)
+(load "lib/smalltalk/tests/runtime.sx")
+(epoch 3)
+(eval "(list st-test-pass st-test-fail)")
+EPOCHS
+
+OUTPUT=$(timeout 60 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
+
+LINE=$(echo "$OUTPUT" | awk '/^\(ok-len 3 / {getline; print; exit}')
+if [ -z "$LINE" ]; then
+  LINE=$(echo "$OUTPUT" | grep -E '^\(ok 3 \([0-9]+ [0-9]+\)\)' | tail -1 \
+          | sed -E 's/^\(ok 3 //; s/\)$//')
+fi
+if [ -z "$LINE" ]; then
+  echo "ERROR: could not extract summary"
+  echo "$OUTPUT" | tail -10
+  exit 1
+fi
+
+P=$(echo "$LINE" | sed -E 's/^\(([0-9]+) ([0-9]+)\).*/\1/')
+F=$(echo "$LINE" | sed -E 's/^\(([0-9]+) ([0-9]+)\).*/\2/')
+TOTAL=$((P + F))
+
+if [ "$F" -eq 0 ]; then
+  echo "ok $P/$TOTAL lib/smalltalk tests passed"
+else
+  echo "FAIL $P/$TOTAL passed, $F failed"
+  # Print failure details
+  TMPFILE2=$(mktemp)
+  cat > "$TMPFILE2" << 'EPOCHS2'
+(epoch 1)
+(load "spec/stdlib.sx")
+(load "lib/smalltalk/runtime.sx")
+(epoch 2)
+(load "lib/smalltalk/tests/runtime.sx")
+(epoch 3)
+(eval "(map (fn (f) (get f \"name\")) st-test-fails)")
+EPOCHS2
+  FAILS=$(timeout 60 "$SX_SERVER" < "$TMPFILE2" 2>/dev/null | grep -E '^\(ok 3 ' || true)
+  rm -f "$TMPFILE2"
+  echo "  Failures: $FAILS"
+fi
+
+[ "$F" -eq 0 ]
diff --git a/lib/smalltalk/tests/runtime.sx b/lib/smalltalk/tests/runtime.sx
new file mode 100644
index 00000000..78dd4e5e
--- /dev/null
+++ b/lib/smalltalk/tests/runtime.sx
@@ -0,0 +1,241 @@
+;; lib/smalltalk/tests/runtime.sx — Tests for lib/smalltalk/runtime.sx
+;;
+;; Uses the same hk-test framework as lib/haskell/tests/runtime.sx.
+;; Load: lib/smalltalk/runtime.sx first.
+
+;; --- Test framework ---
+(define st-test-pass 0)
+(define st-test-fail 0)
+(define st-test-fails (list))
+
+(define
+  (st-test name got expected)
+  (if
+    (= got expected)
+    (set! st-test-pass (+ st-test-pass 1))
+    (begin
+      (set! st-test-fail (+ st-test-fail 1))
+      (set! st-test-fails (append st-test-fails (list {:got got :expected expected :name name}))))))
+
+;; ---------------------------------------------------------------------------
+;; 1. Numeric helpers
+;; ---------------------------------------------------------------------------
+
+(st-test "abs -5" (st-abs -5) 5)
+(st-test "abs 3" (st-abs 3) 3)
+(st-test "max 3 7" (st-max 3 7) 7)
+(st-test "min 3 7" (st-min 3 7) 3)
+(st-test "gcd 12 8" (st-gcd 12 8) 4)
+(st-test "lcm 4 6" (st-lcm 4 6) 12)
+(st-test "quo 10 3" (st-quo 10 3) 3)
+(st-test "quo -10 3" (st-quo -10 3) -3)
+(st-test "rem 10 3" (st-rem 10 3) 1)
+(st-test "rem -10 3" (st-rem -10 3) -1)
+(st-test "mod 10 3" (st-mod 10 3) 1)
+(st-test "mod -10 3" (st-mod -10 3) 2)
+(st-test "even? 4" (st-even? 4) true)
+(st-test "even? 3" (st-even? 3) false)
+(st-test "odd? 7" (st-odd? 7) true)
+(st-test "floor 3.7" (st-floor 3.7) 3)
+(st-test "ceiling 3.2" (st-ceiling 3.2) 4)
+(st-test "truncated 3.9" (st-truncated 3.9) 3)
+(st-test "rounded 3.5" (st-rounded 3.5) 4)
+
+;; ---------------------------------------------------------------------------
+;; 2. Character
+;; ---------------------------------------------------------------------------
+
+(st-test
+  "char-value A"
+  (st-char-value (st-char-from-int 65))
+  65)
+(st-test "char-from-int" (st-char? (st-char-from-int 65)) true)
+(st-test "char? true" (st-char? (integer->char 65)) true)
+(st-test "char? false" (st-char? 65) false)
+(st-test "is-letter? A" (st-char-is-letter? (integer->char 65)) true)
+(st-test
+  "is-letter? 1"
+  (st-char-is-letter? (integer->char 49))
+  false)
+(st-test "is-digit? 5" (st-char-is-digit? (integer->char 53)) true)
+(st-test "is-digit? A" (st-char-is-digit? (integer->char 65)) false)
+(st-test
+  "is-uppercase? A"
+  (st-char-is-uppercase? (integer->char 65))
+  true)
+(st-test
+  "is-uppercase? a"
+  (st-char-is-uppercase? (integer->char 97))
+  false)
+(st-test
+  "is-lowercase? a"
+  (st-char-is-lowercase? (integer->char 97))
+  true)
+(st-test
+  "is-lowercase? A"
+  (st-char-is-lowercase? (integer->char 65))
+  false)
+(st-test
+  "is-separator? sp"
+  (st-char-is-separator? (integer->char 32))
+  true)
+(st-test
+  "is-separator? A"
+  (st-char-is-separator? (integer->char 65))
+  false)
+(st-test
+  "as-uppercase a"
+  (st-char-value (st-char-as-uppercase (integer->char 97)))
+  65)
+(st-test
+  "as-uppercase A"
+  (st-char-value (st-char-as-uppercase (integer->char 65)))
+  65)
+(st-test
+  "as-lowercase A"
+  (st-char-value (st-char-as-lowercase (integer->char 65)))
+  97)
+(st-test
+  "digit-value 5"
+  (st-char-digit-value (integer->char 53))
+  5)
+
+;; ---------------------------------------------------------------------------
+;; 3. Array
+;; ---------------------------------------------------------------------------
+
+(st-test
+  "array-new size"
+  (st-array-size (st-array-new 5))
+  5)
+(st-test "array? yes" (st-array? (st-array-new 3)) true)
+(st-test "array? no" (st-array? 42) false)
+(st-test
+  "array-at nil"
+  (st-array-at (st-array-new 3) 1)
+  nil)
+
+(let
+  ((a (st-array-new 3)))
+  (st-array-at-put! a 1 10)
+  (st-array-at-put! a 2 20)
+  (st-array-at-put! a 3 30)
+  (st-test "array-at 1" (st-array-at a 1) 10)
+  (st-test "array-at 2" (st-array-at a 2) 20)
+  (st-test "array-at 3" (st-array-at a 3) 30))
+
+(st-test
+  "list->array->list"
+  (st-array->list (st-list->array (list 1 2 3)))
+  (list 1 2 3))
+
+(let
+  ((a (st-list->array (list 10 20 30 40 50))))
+  (st-test
+    "copy-from-to"
+    (st-array->list (st-array-copy-from-to a 2 4))
+    (list 20 30 40)))
+
+;; ---------------------------------------------------------------------------
+;; 4. Dictionary
+;; ---------------------------------------------------------------------------
+
+(st-test "dict? yes" (st-dict? (st-dict-new)) true)
+(st-test "dict? no" (st-dict? 42) false)
+(st-test "dict empty size" (st-dict-size (st-dict-new)) 0)
+(st-test "dict at absent" (st-dict-at (st-dict-new) "k") nil)
+
+(let
+  ((d (st-dict-new)))
+  (st-dict-at-put! d "a" 1)
+  (st-dict-at-put! d "b" 2)
+  (st-test "dict at a" (st-dict-at d "a") 1)
+  (st-test "dict at b" (st-dict-at d "b") 2)
+  (st-test "dict size 2" (st-dict-size d) 2)
+  (st-test "includes-key? yes" (st-dict-includes-key? d "a") true)
+  (st-test "includes-key? no" (st-dict-includes-key? d "z") false)
+  (st-dict-at-put! d "a" 99)
+  (st-test "dict update" (st-dict-at d "a") 99)
+  (st-test "size unchanged" (st-dict-size d) 2)
+  (st-dict-remove-key! d "a")
+  (st-test "size after remove" (st-dict-size d) 1)
+  (st-test "at-default hit" (st-dict-at-default d "b" 0) 2)
+  (st-test "at-default miss" (st-dict-at-default d "z" -1) -1))
+
+;; ---------------------------------------------------------------------------
+;; 5. Set
+;; ---------------------------------------------------------------------------
+
+(st-test "set? yes" (st-set? (st-set-new)) true)
+(st-test "set? no" (st-set? 42) false)
+(st-test "set empty size" (st-set-size (st-set-new)) 0)
+
+(let
+  ((s (st-set-new)))
+  (st-set-add! s 1)
+  (st-set-add! s 2)
+  (st-set-add! s 1)
+  (st-test "set includes 1" (st-set-includes? s 1) true)
+  (st-test "set includes 2" (st-set-includes? s 2) true)
+  (st-test "set not includes 3" (st-set-includes? s 3) false)
+  (st-test "set dedup size" (st-set-size s) 2)
+  (st-set-remove! s 1)
+  (st-test "size after remove" (st-set-size s) 1)
+  (st-test "removed gone" (st-set-includes? s 1) false))
+
+;; ---------------------------------------------------------------------------
+;; 6. String / Stream
+;; ---------------------------------------------------------------------------
+
+(st-test "join-strings 3" (st-join-strings (list "a" "b" "c") "-") "a-b-c")
+(st-test "join-strings 1" (st-join-strings (list "x") ",") "x")
+(st-test "join-strings empty" (st-join-strings (list) ",") "")
+
+(st-test "print nil" (st-print-string nil) "nil")
+(st-test "print true" (st-print-string true) "true")
+(st-test "print false" (st-print-string false) "false")
+(st-test "print number" (st-print-string 42) "42")
+(st-test "print string" (st-print-string "hi") "'hi'")
+(st-test "print char" (st-print-string (integer->char 65)) "$A")
+(st-test "print list" (st-print-string (list 1 2)) "(1 2)")
+
+(let
+  ((ws (st-write-stream-new)))
+  (st-write-stream-put-string! ws "hello")
+  (st-write-stream-put-string! ws " world")
+  (st-test
+    "write-stream contents"
+    (st-write-stream-contents ws)
+    "hello world"))
+
+(let
+  ((ws (st-write-stream-new)))
+  (st-write-stream-next-put! ws (integer->char 72))
+  (st-write-stream-next-put! ws (integer->char 105))
+  (st-test "write-stream next-put!" (st-write-stream-contents ws) "Hi"))
+
+(let
+  ((rs (st-read-stream-new "ABC")))
+  (st-test
+    "read-stream next A"
+    (st-char-value (st-read-stream-next rs))
+    65)
+  (st-test
+    "read-stream next B"
+    (st-char-value (st-read-stream-next rs))
+    66)
+  (st-test
+    "read-stream peek C"
+    (st-char-value (st-read-stream-peek rs))
+    67)
+  (st-test
+    "read-stream next C"
+    (st-char-value (st-read-stream-next rs))
+    67)
+  (st-test "read-stream at-end" (st-read-stream-at-end? rs) true))
+
+;; ---------------------------------------------------------------------------
+;; Summary (must be last form — test.sh reads this)
+;; ---------------------------------------------------------------------------
+
+(list st-test-pass st-test-fail)
diff --git a/plans/agent-briefings/primitives-loop.md b/plans/agent-briefings/primitives-loop.md
index c10e6a92..a608a46f 100644
--- a/plans/agent-briefings/primitives-loop.md
+++ b/plans/agent-briefings/primitives-loop.md
@@ -694,8 +694,9 @@ Brief each language's loop agent (or do inline) after rebasing their branch onto
       arrays; regexp for JS regex; bytevectors for `Uint8Array`; radix formatting.
       lib/js/stdlib.sx (36 forms) + test.sh epochs 6000-6032 (25/25 pass). COMMIT.
 
-- [ ] Smalltalk: vectors for `Array new:`; hash tables for `Dictionary new`; sets for
+- [x] Smalltalk: vectors for `Array new:`; hash tables for `Dictionary new`; sets for
       `Set new`; char type for `Character`; string ports + `read`/`write` for `printString`.
+      lib/smalltalk/runtime.sx (72 forms) + tests/runtime.sx (86/86 pass). COMMIT.
 
 - [ ] APL: vectors as core array type; bitwise ops for array masks; sets for APL set ops;
       sequence protocol for rank-polymorphic operations; format for APL output formatting.
@@ -725,6 +726,7 @@ Brief each language's loop agent (or do inline) after rebasing their branch onto
 
 _Newest first._
 
+- 2026-05-01: Phase 22 Smalltalk done — runtime.sx (72 forms): numeric helpers, Character (1-indexed Array backed by dict), Dictionary (list-of-pairs any-key map), Set (make-set), WriteStream/ReadStream/printString. set-member? (set item) order. 86/86 tests. COMMIT.
 - 2026-05-01: Phase 22 JS done — stdlib.sx (36 forms): bitwise (truncate not js-num-to-int; set-member? takes (set item) order), Map (dict-backed pairs), Set (SX make-set), RegExp (callable lambda). 25/25 new tests pass; total 492/585. COMMIT.
 - 2026-05-01: Phase 22 Haskell done — runtime.sx (113 forms): numeric tower (hk-div floor semantics), rational (dict GCD-normalised), hk-force (promises), Data.Char, Data.Set, Data.List, Maybe/Either, tuples, string helpers, hk-show. 148/148 tests. c02ffcf3.
 - 2026-05-01: Phase 22 Erlang done — runtime.sx (63 forms): numeric tower, bitwise (band/bor/bxor/bnot/bsl/bsr), sets, re module, list BIFs, type conversions, ok/error tuples. 55/55 tests. 3c0a9632.