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) {

lang/el-compiler/runtime/el_runtime.h

@@ -750,6 +750,10 @@ el_val_t exec_capture(el_val_t cmd);   /* run shell command, capture stdout   */
 el_val_t exec(el_val_t cmd);           /* exec(cmd) → stdout String (30s timeout) */
 el_val_t exec_bg(el_val_t cmd);        /* exec_bg(cmd) → PID String (non-blocking) */
 
+/* ── Stdout redirection (used by compiler JS pipeline) ───────────────────── */
+el_val_t stdout_to_file(el_val_t path); /* redirect process stdout to a file  */
+el_val_t stdout_restore(void);          /* restore process stdout to terminal  */
+
 el_val_t emit_log(el_val_t level, el_val_t msg, el_val_t fields_json);
 el_val_t emit_metric(el_val_t name, el_val_t value, el_val_t tags_json);
 el_val_t trace_span_start(el_val_t name);