Migrate remaining 7 ref endpoints to SX, add :returns type annotations

Add 14 new IO primitives to boundary.sx: web interop (request-form,
request-json, request-header, request-content-type, request-args-all,
request-form-all, request-headers-all, request-file-name), response
manipulation (set-response-header, set-response-status), ephemeral
state (state-get, state-set!), and timing (now, sleep).

All 19 reference handlers now have :returns type annotations using
types.sx vocabulary. Response meta (headers/status) flows through
context vars, applied by register_route_handlers after execution.

Only SSE endpoint remains in Python (async generator paradigm).

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

shared/sx/ref/boundary.sx

@@ -176,6 +176,66 @@
   :doc "Content-Type of the current request."
   :context :request)
 
+(define-io-primitive "request-args-all"
+  :params ()
+  :returns "dict"
+  :async true
+  :doc "All query string parameters as a dict."
+  :context :request)
+
+(define-io-primitive "request-form-all"
+  :params ()
+  :returns "dict"
+  :async true
+  :doc "All form fields as a dict."
+  :context :request)
+
+(define-io-primitive "request-headers-all"
+  :params ()
+  :returns "dict"
+  :async true
+  :doc "All request headers as a dict (lowercase keys)."
+  :context :request)
+
+(define-io-primitive "request-file-name"
+  :params (field-name)
+  :returns "string?"
+  :async true
+  :doc "Filename of an uploaded file by field name, or nil."
+  :context :request)
+
+;; Response manipulation
+
+(define-io-primitive "set-response-header"
+  :params (name value)
+  :returns "nil"
+  :async true
+  :doc "Set a response header. Applied after handler returns."
+  :context :request)
+
+(define-io-primitive "set-response-status"
+  :params (status)
+  :returns "nil"
+  :async true
+  :doc "Set the HTTP response status code. Applied after handler returns."
+  :context :request)
+
+;; Ephemeral state — per-process, resets on restart
+
+(define-io-primitive "state-get"
+  :params (key &rest default)
+  :returns "any"
+  :async true
+  :doc "Read from ephemeral per-process state dict."
+  :context :request)
+
+(define-io-primitive "state-set!"
+  :params (key value)
+  :returns "nil"
+  :async true
+  :doc "Write to ephemeral per-process state dict."
+  :context :request)
+
 
 ;; --------------------------------------------------------------------------
 ;; Tier 3: Signal primitives — reactive state for islands