spec: read/write/display — S-expression reader/writer on ports

Adds read, write, display, newline, write-to-string, display-to-string
and current-*-port primitives to both JS and OCaml hosts.

JS: sxReadNormalize (#t/#f→true/false), sxReadConvert (()→nil),
    sxEq array comparison, sxWriteVal symbol/keyword name fix,
    readerMacroGet/readerMacroSet registry in parser platform.
OCaml: sx_write_val/sx_display_val helpers, read/write/display/newline
    primitives on port types; parser extended for #t/#f and N/D rationals.
42 new tests (test-read-write.sx), all passing on JS and OCaml.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

spec/primitives.sx

@@ -948,6 +948,61 @@
   :returns "boolean"
   :doc "True if a char is immediately available on the port.")
 
+
+(define-primitive
+  "read"
+  :params (&rest (p :as input-port))
+  :returns "any"
+  :doc "Read one datum from port; returns eof-object at end.")
+
+(define-primitive
+  "write"
+  :params (v &rest (p :as output-port))
+  :returns "nil"
+  :doc "Serialize v to port with quoting — strings quoted, chars as #\\a notation.")
+
+(define-primitive
+  "display"
+  :params (v &rest (p :as output-port))
+  :returns "nil"
+  :doc "Serialize v to port without quoting — strings unquoted, chars as characters.")
+
+(define-primitive
+  "newline"
+  :params (&rest (p :as output-port))
+  :returns "nil"
+  :doc "Write a newline to port.")
+
+(define-primitive
+  "write-to-string"
+  :params (v)
+  :returns "string"
+  :doc "Serialize v with write quoting, return as string.")
+
+(define-primitive
+  "display-to-string"
+  :params (v)
+  :returns "string"
+  :doc "Serialize v with display format, return as string.")
+
+(define-primitive
+  "current-input-port"
+  :params ()
+  :returns "any"
+  :doc "Return current default input port.")
+
+(define-primitive
+  "current-output-port"
+  :params ()
+  :returns "any"
+  :doc "Return current default output port.")
+
+(define-primitive
+  "current-error-port"
+  :params ()
+  :returns "any"
+  :doc "Return current error port.")
+
 (define-module :stdlib.math)
 
 (define-primitive