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>

tests/playwright/generate-sx-tests.py

@@ -1894,6 +1894,40 @@ def generate_eval_only_test(test, idx):
             f'    (assert (nil? (eval-hs "cookies.foo"))))'
         )
 
+    # Special case: cluster-36 socket URL tests. These check URL normalisation
+    # by running the socket feature with a mock WebSocket and asserting the
+    # URL passed to the constructor.
+    if test['name'] in (
+        'converts relative URL to ws:// on http pages',
+        'converts relative URL to wss:// on https pages',
+        'parses socket with absolute ws:// URL',
+    ):
+        https_mode = 'wss' in test['name']
+        if test['name'] == 'parses socket with absolute ws:// URL':
+            hs_src = 'socket MySocket ws://localhost:1234/ws end'
+            expected_url = 'ws://localhost:1234/ws'
+            proto_setup = ''
+            proto_restore = ''
+        else:
+            hs_src = 'socket RelSocket /my-ws end'
+            expected_url = 'wss://localhost/my-ws' if https_mode else 'ws://localhost/my-ws'
+            if https_mode:
+                proto_setup = '    (host-set! (host-global "location") "protocol" "https:")\n'
+                proto_restore = '    (host-set! (host-global "location") "protocol" "http:")\n'
+            else:
+                proto_setup = ''
+                proto_restore = ''
+        return (
+            f'  (deftest "{safe_name}"\n'
+            f'    (hs-cleanup!)\n'
+            f'    (host-set! (host-global "window") "__hs_ws_created" (list))\n'
+            + proto_setup +
+            f'    (eval-hs "{hs_src}")\n'
+            + proto_restore +
+            f'    (let ((sock (host-get (host-global "__hs_ws_created") 0)))\n'
+            f'      (assert= (host-get sock "url") "{expected_url}")))' 
+        )
+
     # Special case: cluster-29 init events. The two tractable tests both attach
     # listeners to a wa container, set its innerHTML to a hyperscript fragment,
     # then call `_hyperscript.processNode(wa)`. Hand-roll deftests using