fix(codegen): escape C++ string literals (quotes/backslash/newline)

pineforge_codegen/codegen/base.py

@@ -1258,7 +1258,7 @@ def _resolve_known(self, arg_str: str) -> str:
             if isinstance(val, (int, float)):
                 return str(val)
             if isinstance(val, str):
-                return f'std::string("{val}")'
+                return f'std::string("{self._cpp_string_escape(val)}")'
         # Also resolve bar field references
         if arg_str in BAR_FIELDS:
             return BAR_FIELDS[arg_str]

pineforge_codegen/codegen/visit_expr.py

@@ -180,7 +180,7 @@ def _visit_expr(self, node: ASTNode | None) -> str:
         if isinstance(node, NumberLiteral):
             return str(node.value)
         if isinstance(node, StringLiteral):
-            return f'std::string("{node.value}")'
+            return f'std::string("{self._cpp_string_escape(node.value)}")'
         if isinstance(node, BoolLiteral):
             return "true" if node.value else "false"
         if isinstance(node, NaLiteral):

tests/test_codegen_string_escape.py

@@ -0,0 +1,25 @@
+"""Regression: C++ string-literal escaping.
+
+Pine strings may contain characters that are special inside a C++ string
+literal — double quotes (common in JSON alert/webhook templates), backslashes,
+and newlines. These must be escaped when emitted, or the generated C++ fails to
+compile ("invalid suffix on literal" / unterminated string).
+"""
+
+from pineforge_codegen import transpile
+
+
+def _cpp(body: str) -> str:
+    return transpile('//@version=6\nstrategy("t")\n' + body + "\n")
+
+
+def test_string_with_embedded_double_quotes_is_escaped():
+    cpp = _cpp("msg = '{\"type\":\"bot\",\"id\":\"42\"}'\nplot(str.length(msg))")
+    # The raw inner quotes must be backslash-escaped in the C++ literal.
+    assert r'\"type\"' in cpp
+    assert 'std::string("{"type"' not in cpp  # the broken (unescaped) form
+
+
+def test_string_with_backslash_is_escaped():
+    cpp = _cpp("p = 'a\\\\b'\nplot(str.length(p))")
+    assert "\\\\" in cpp