HS E36: socket URL parsing + hs-socket-register! runtime (+3 tests)

- parser.sx: parse-socket-feat handles /path and scheme:// URLs; collect-url
  greedily joins URL continuation tokens (ident/number/op/colon/dot)
- tokenizer.sx: fix :// not treated as line comment (lookback check)
- compiler.sx: emit-socket compiles socket AST to hs-socket-register! call
- runtime.sx: hs-socket-register! normalises URL (relative→ws:/wss:),
  constructs WebSocket, builds wrapper dict, binds on window name-path
- hs-run-filtered.js: WebSocket mock uses plain object (not JS array) so
  host-global returns a foreign value rather than SX list; host-get idx works

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

shared/static/wasm/sx/hs-parser.sx

@@ -2729,6 +2729,63 @@
                   (match-kw "end")
                   (list (quote when-feat-no-op)))))
             (do (pwf-skip) (match-kw "end") (list (quote when-feat-no-op))))))
+      (define
+        parse-socket-feat
+        (fn
+          ()
+          (let
+            ((seg0 (tp-val)))
+            (adv!)
+            (define
+              collect-segs
+              (fn
+                (acc)
+                (if
+                  (= (tp-type) "class")
+                  (let
+                    ((seg (tp-val)))
+                    (adv!)
+                    (collect-segs (append acc (list seg))))
+                  acc)))
+            (let
+              ((name-path (collect-segs (list seg0))))
+              (define
+                url-cont?
+                (fn
+                  ()
+                  (or
+                    (= (tp-type) "ident")
+                    (= (tp-type) "number")
+                    (= (tp-type) "op")
+                    (= (tp-type) "colon")
+                    (= (tp-type) "dot")
+                    (and
+                      (= (tp-type) "keyword")
+                      (not
+                        (or
+                          (= (tp-val) "end")
+                          (= (tp-val) "with")
+                          (= (tp-val) "on")
+                          (= (tp-val) "as")))))))
+              (define
+                collect-url
+                (fn
+                  (parts)
+                  (if
+                    (and (not (at-end?)) (url-cont?))
+                    (let
+                      ((v (tp-val)))
+                      (adv!)
+                      (collect-url (append parts (list v))))
+                    (join "" parts))))
+              (let
+                ((url (cond ((and (= (tp-type) "op") (= (tp-val) "/")) (do (adv!) (collect-url (list "/")))) ((= (tp-type) "ident") (let ((scheme (tp-val))) (adv!) (if (= (tp-type) "colon") (collect-url (list scheme)) (parse-arith (parse-poss (list (quote ref) scheme)))))) (true (parse-atom)))))
+                (let
+                  ((timeout-ms (if (match-kw "with") (do (adv!) (parse-expr)) nil)))
+                  (let
+                    ((on-msg (if (match-kw "on") (do (adv!) (let ((json? (if (match-kw "as") (do (adv!) true) false))) (let ((body (parse-cmd-list))) (list (quote on-message) json? body)))) nil)))
+                    (match-kw "end")
+                    (list (quote socket) name-path url timeout-ms on-msg))))))))
       (define
         parse-feat
         (fn
@@ -2749,6 +2806,7 @@
               ((= val "behavior") (do (adv!) (parse-behavior-feat)))
               ((= val "live") (do (adv!) (parse-live-feat)))
               ((= val "when") (do (adv!) (parse-when-feat)))
+              ((= val "socket") (do (adv!) (parse-socket-feat)))
               (true (parse-cmd-list))))))
       (define
         coll-feats