HS: sieve test compile-once + string-var expansion in generator

Replace 11 separate eval-hs-locals compilations with a single
hs-compile call + shared run-sieve fn; reduces wall-clock from
60s+ to ~1s per call.

Generator: pre-resolve string variable concatenations before
pattern matching run() calls so multi-line HS sources translate
correctly.

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

tests/playwright/generate-sx-tests.py

@@ -2590,6 +2590,27 @@ def generate_eval_only_test(test, idx):
 
     assertions = []
 
+    # Pre-resolve string variable assignments: `var str = "..." + "..." + ...`
+    # so that `run(str, opts)` is treated the same as `run("expanded", opts)`.
+    # JS `\n` / `\t` escape sequences in the joined value are collapsed to spaces
+    # since HS uses keyword delimiters (if/else/end/then), not indentation.
+    _str_vars = {}
+    for _sv in re.finditer(
+        r'(?:var|let|const)\s+(\w+)\s*=\s*((?:"(?:[^"\\]|\\.)*"|\'(?:[^\'\\]|\\.)*\'|\s*\+\s*)+)\s*;',
+        body, re.DOTALL
+    ):
+        _vname = _sv.group(1)
+        _raw = _sv.group(2)
+        _parts = re.findall(r'"((?:[^"\\]|\\.)*?)"|\'((?:[^\'\\]|\\.)*?)\'', _raw)
+        _joined = ''.join(p[0] or p[1] for p in _parts)
+        # Collapse JS newline/tab escapes to spaces so the HS source is flat.
+        _joined = _joined.replace('\\n', ' ').replace('\\t', ' ')
+        _str_vars[_vname] = _joined
+    if _str_vars:
+        for _vname, _val in _str_vars.items():
+            _escaped = _val.replace('"', '\\"')
+            body = re.sub(r'\brun\(' + re.escape(_vname) + r'\b', f'run("{_escaped}"', body)
+
     # Window setups from `evaluate(() => { window.X = Y })` blocks.
     # These get merged into local_pairs so the HS expression can reference them.
     window_setups = extract_window_setups(body)