HS-gen: string-aware line-comment stripping (+1 test)

process_hs_val stripped `//…` line comments with a naïve regex,
which devoured `https://yyy.xxxxxx.com/…` inside a backtick template
— the 'properly interpolates values 2' fixture was landing with
the HS source truncated at `https:`.

New helper _strip_hs_line_comments walks char-by-char and only
strips `//` / leading-whitespace `--` when not inside `'…'`, `"…"`,
or backticks; respects `\\`-escapes inside strings.

Suite hs-upstream-core/regressions: 11/16 → 12/16.
Smoke 0-195: 163/195 → 164/195.

tests/playwright/generate-sx-tests.py

@@ -1177,6 +1177,45 @@ def parse_dev_body(body, elements, var_names):
 
 # ── Test generation ───────────────────────────────────────────────
 
+def _strip_hs_line_comments(s):
+    """Strip `//…` and `--…` line comments outside HS string literals.
+
+    HS has three string delimiters: single quotes, double quotes, and
+    backticks (template strings). `https://…` inside a backtick must not
+    be treated as a comment.
+    """
+    out = []
+    i = 0
+    n = len(s)
+    in_str = None  # None | "'" | '"' | '`'
+    while i < n:
+        ch = s[i]
+        if in_str is None:
+            # Check for line-comment starters at depth 0.
+            if ch == '/' and i + 1 < n and s[i + 1] == '/':
+                # Skip to newline.
+                while i < n and s[i] != '\n':
+                    i += 1
+                continue
+            if ch == '-' and i + 1 < n and s[i + 1] == '-' and (i == 0 or s[i - 1].isspace()):
+                while i < n and s[i] != '\n':
+                    i += 1
+                continue
+            if ch in ("'", '"', '`'):
+                in_str = ch
+            out.append(ch)
+            i += 1
+        else:
+            if ch == '\\' and i + 1 < n:
+                out.append(ch); out.append(s[i + 1]); i += 2
+                continue
+            if ch == in_str:
+                in_str = None
+            out.append(ch)
+            i += 1
+    return ''.join(out)
+
+
 def process_hs_val(hs_val):
     """Process a raw HS attribute value: collapse whitespace, insert 'then' separators."""
     # Convert escaped newlines/tabs to real whitespace
@@ -1187,8 +1226,8 @@ def process_hs_val(hs_val):
     hs_val = hs_val.replace('\x00QUOT\x00', '\\"')
     # Strip line comments BEFORE newline collapse — once newlines become `then`,
     # an unterminated `//` / ` --` comment would consume the rest of the input.
-    hs_val = re.sub(r'//[^\n]*', '', hs_val)
-    hs_val = re.sub(r'(^|\s)--[^\n]*', r'\1', hs_val)
+    # String-aware: `https://…` inside a backtick template must not be stripped.
+    hs_val = _strip_hs_line_comments(hs_val)
     cmd_kws = r'(?:set|put|get|add|remove|toggle|hide|show|if|repeat|for|wait|send|trigger|log|call|take|throw|return|append|tell|go|halt|settle|increment|decrement|fetch|make|install|measure|empty|reset|swap|default|morph|render|scroll|focus|select|pick|beep!)'
     hs_val = re.sub(r'\s{2,}(?=' + cmd_kws + r'\b)', ' then ', hs_val)
     hs_val = re.sub(r'\s*[\n\r]\s*', ' then ', hs_val)