metadata times: -U/--atimes, -N/--crtimes, --open-noatime, -O/-J

Capture+transmit source atime (pre-read stat; O_NOATIME sender guard) and birth
time (statx STATX_BTIME); receiver restores atime with mtime (crtime not settable
portably -> transmitted, explicitly not applied). --open-noatime is client-only.
-O/-J documented as accepted no-ops (FastSync never preserves dir/symlink times).
Wire: metadata frame gains atime/crtime val+sec+nsec; PROTOCOL_VERSION
2.11.0->2.12.0. Review fixes: gate atime capture to Linux (no epoch clobber on
non-Linux), close fd on fdopen failure, honest -O/-J status (Compat no-op).

src/shared/config.c

@@ -148,6 +148,11 @@ static void config_set_defaults(Config* config) {
   config->groupmap = NULL;
   config->groupmap_count = 0;
   config->delay_context = NULL;
+  config->preserve_atimes = false;
+  config->preserve_crtimes = false;
+  config->omit_dir_times = false;
+  config->omit_link_times = false;
+  config->open_noatime = false;
 }
 
 static bool valid_wire_bool(int value) {
@@ -195,6 +200,8 @@ static bool validate_received_config(const Config* config) {
             which chunk serialization -s disables: reject on the receiver too
             so a -s sender cannot negotiate an inert append mode. */
          !((config->append || config->append_verify) && config->use_chunk_serialization) &&
+         valid_wire_bool(config->preserve_atimes) && valid_wire_bool(config->preserve_crtimes) &&
+         valid_wire_bool(config->omit_dir_times) && valid_wire_bool(config->omit_link_times) &&
          (!config->use_compression ||
           (config->compression_level >= 1 && config->compression_level <= 22)) &&
          config->chunk_size > 0 && config->chunk_size <= MAX_CHUNK_SIZE &&
@@ -746,6 +753,22 @@ static bool receive_identity_options(int fd, Config* c) {
          receive_identity_map(fd, &c->groupmap_count, &c->groupmap);
 }
 
+/* -U/--atimes, -N/--crtimes (affect both sender capture and receiver apply)
+ * and -O/--omit-dir-times, -J/--omit-link-times (receiver-side prefs) all cross
+ * the wire so the receiver knows what to apply / suppress.  --open-noatime is
+ * client-only (it only governs the sender's source reads) and is never
+ * serialized.  Trailing fields; protocol 2.12.0. */
+static bool send_metadata_times_options(int fd, const Config* c) {
+  return send_int(fd, c->preserve_atimes) && send_int(fd, c->preserve_crtimes) &&
+         send_int(fd, c->omit_dir_times) && send_int(fd, c->omit_link_times);
+}
+
+static bool receive_metadata_times_options(int fd, Config* c) {
+  return receive_wire_bool(fd, &c->preserve_atimes) &&
+         receive_wire_bool(fd, &c->preserve_crtimes) && receive_wire_bool(fd, &c->omit_dir_times) &&
+         receive_wire_bool(fd, &c->omit_link_times);
+}
+
 bool config_send(int file_descriptor, const Config* config) {
   protocol_session_set_max_alloc(NULL, config->max_alloc);
   if (!send_core_fields(file_descriptor, config) || !send_delta_fields(file_descriptor, config) ||
@@ -754,7 +777,8 @@ bool config_send(int file_descriptor, const Config* config) {
       !send_resume_options(file_descriptor, config) ||
       !send_basis_options(file_descriptor, config) || !send_fuzzy_option(file_descriptor, config) ||
       !send_checksum_options(file_descriptor, config) ||
-      !send_identity_options(file_descriptor, config))
+      !send_identity_options(file_descriptor, config) ||
+      !send_metadata_times_options(file_descriptor, config))
     return false;
   Status status;
   if (!receive_status(file_descriptor, &status))
@@ -790,7 +814,8 @@ Config* config_receive(int file_descriptor) {
       !receive_basis_options(file_descriptor, config) ||
       !receive_fuzzy_option(file_descriptor, config) ||
       !receive_checksum_options(file_descriptor, config) ||
-      !receive_identity_options(file_descriptor, config))
+      !receive_identity_options(file_descriptor, config) ||
+      !receive_metadata_times_options(file_descriptor, config))
     goto error;
   if (config->compress_choice[0] != '\0' && strcmp(config->compress_choice, "zstd") != 0 &&
       strcmp(config->compress_choice, "none") != 0) {