fix: codegen O(n²) HTML memory leak + elb stderr surface + runtime dir path

lang/el-compiler/runtime/el_runtime.c

@@ -1887,6 +1887,34 @@ el_val_t fs_write_bytes(el_val_t pathv, el_val_t bytesv, el_val_t lengthv) {
     return 1;
 }
 
+// stdout_to_file / stdout_restore — redirect process stdout to a file and
+// restore it. Used by the compiler's JS post-processing pipeline to capture
+// codegen output before piping through terser / obfuscator.
+#include <fcntl.h>
+static int _el_saved_stdout_fd = -1;
+
+el_val_t stdout_to_file(el_val_t pathv) {
+    const char* path = EL_CSTR(pathv);
+    if (!path) return (el_val_t)(int64_t)-1;
+    fflush(stdout);
+    _el_saved_stdout_fd = dup(STDOUT_FILENO);
+    int fd = open(path, O_WRONLY | O_CREAT | O_TRUNC, 0600);
+    if (fd < 0) return (el_val_t)(int64_t)-1;
+    dup2(fd, STDOUT_FILENO);
+    close(fd);
+    return (el_val_t)(int64_t)0;
+}
+
+el_val_t stdout_restore(void) {
+    if (_el_saved_stdout_fd >= 0) {
+        fflush(stdout);
+        dup2(_el_saved_stdout_fd, STDOUT_FILENO);
+        close(_el_saved_stdout_fd);
+        _el_saved_stdout_fd = -1;
+    }
+    return (el_val_t)(int64_t)0;
+}
+
 // exec_command — run a shell command, return exit code (0 = success).
 // Used by elb and other El tooling to invoke subprocesses.
 el_val_t exec_command(el_val_t cmdv) {