HS: runtimeErrors suite 18/18 — null error reporting fixes

- parser: settle command now parses optional CSS selector target
  (was hardcoded to me; #doesntExist was parsed as a separate expression)
- compiler: emit-set case 1 handles poss nodes for property assignment
- compiler: emit-set selector side-channel writes to window._hs_last_query_sel
  via host-set! (was dead SX variable set!)
- compiler: dot-call dispatch accepts poss nodes; poss hs-to-sx case added
- runtime: hs-query-first/hs-query-all fn bodies wrapped in (do ...) so
  host-set! _hs_last_query_sel runs (JIT compiles only last fn body expression)
- runtime: hs-set-inner-html! null-checks target before writing
- runtime: hs-query-all-checked body wrapped in (do ...) so hs-empty-raise!
  is not dead code (SX let evaluates only last body expression)
- parser: parse-poss-tail and parse-prop-chain produce poss nodes for 's access
- tests: predefine x/y/z as nil to prevent undef-sym exceptions escaping guard
- tests: NO_STEP_LIMIT_SUITES includes runtimeErrors

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

lib/hyperscript/parser.sx

@@ -71,12 +71,14 @@
             ((typ (tp-type)) (val (tp-val)))
             (cond
               ((or (= typ "ident") (= typ "keyword"))
-                (do (adv!) (parse-prop-chain (list (quote .) owner val))))
+                (do
+                  (adv!)
+                  (parse-prop-chain (list (quote poss) owner val))))
               ((= typ "attr") (do (adv!) (list (quote attr) val owner)))
               ((= typ "class")
                 (let
                   ((prop (get (adv!) "value")))
-                  (parse-prop-chain (list (quote .) owner prop))))
+                  (parse-prop-chain (list (quote poss) owner prop))))
               ((= typ "style") (do (adv!) (list (quote style) val owner)))
               (true owner)))))
       (define
@@ -116,7 +118,18 @@
                       (prev-end)
                       base-line
                       {:root base})))
-                base)))))
+                (if
+                  (and
+                    (= (tp-type) "op")
+                    (= (tp-val) "'s")
+                    (not (at-end?)))
+                  (let
+                    ((poss-prop (begin (adv!) (tp-val))))
+                    (do
+                      (adv!)
+                      (parse-prop-chain
+                        (list (make-symbol "poss") base poss-prop))))
+                  base))))))
       (define
         parse-trav
         (fn
@@ -429,8 +442,7 @@
                   (let
                     ((name val) (args (parse-call-args)))
                     (cons (quote call) (cons (list (quote ref) name) args)))))
-              ((= typ "keyword")
-                (do (adv!) (list (quote ref) val)))
+              ((= typ "keyword") (do (adv!) (list (quote ref) val)))
               (true nil)))))
       (define
         parse-poss
@@ -443,10 +455,13 @@
             ((= (tp-type) "dot")
               (do
                 (adv!)
-                (let ((typ2 (tp-type)) (val2 (tp-val)))
+                (let
+                  ((typ2 (tp-type)) (val2 (tp-val)))
                   (if
                     (or (= typ2 "ident") (= typ2 "keyword"))
-                    (do (adv!) (parse-poss (list (make-symbol ".") obj val2)))
+                    (do
+                      (adv!)
+                      (parse-poss (list (make-symbol ".") obj val2)))
                     obj))))
             ((= (tp-type) "paren-open")
               (let
@@ -1475,7 +1490,8 @@
                 ((match-kw "to")
                   (let
                     ((value (parse-expr)))
-                    (if (and (list? tgt) (= (first tgt) (quote query)))
+                    (if
+                      (and (list? tgt) (= (first tgt) (quote query)))
                       (list (quote set-el!) tgt value)
                       (list (quote set!) tgt value))))
                 ((match-kw "on")
@@ -2648,7 +2664,14 @@
               ((and (= typ "keyword") (= val "answer"))
                 (do (adv!) (parse-answer-cmd)))
               ((and (= typ "keyword") (= val "settle"))
-                (do (adv!) (list (quote settle))))
+                (do
+                  (adv!)
+                  (let
+                    ((tgt (cond ((at-end?) nil) ((and (= (tp-type) "keyword") (or (= (tp-val) "then") (= (tp-val) "end") (= (tp-val) "with") (= (tp-val) "when") (= (tp-val) "on"))) nil) (true (parse-expr)))))
+                    (if
+                      (nil? tgt)
+                      (list (quote settle))
+                      (list (quote settle) tgt)))))
               ((and (= typ "keyword") (= val "go"))
                 (do (adv!) (parse-go-cmd)))
               ((and (= typ "keyword") (= val "return"))
@@ -2716,9 +2739,11 @@
                   (adv!)
                   (expect-kw! "view")
                   (expect-kw! "transition")
-                  (let ((using (if (match-kw "using") (parse-expr) nil)))
+                  (let
+                    ((using (if (match-kw "using") (parse-expr) nil)))
                     (match-kw "then")
-                    (let ((body (parse-cmd-list)))
+                    (let
+                      ((body (parse-cmd-list)))
                       (match-kw "end")
                       (list (quote view-transition!) using body)))))
               (true (parse-expr))))))
@@ -2882,7 +2907,11 @@
                                     (true nil))))
                               (true nil))))
                         (consume-having!)
-                        (when (and (= (tp-type) "keyword") (= (tp-val) "queue")) (do (adv!) (adv!)))
+                        (when
+                          (and
+                            (= (tp-type) "keyword")
+                            (= (tp-val) "queue"))
+                          (do (adv!) (adv!)))
                         (let
                           ((having (if (or h-margin h-threshold) (dict "margin" h-margin "threshold" h-threshold) nil)))
                           (let