symlink-trust: -k/--copy-dirlinks, -K/--keep-dirlinks, --munge-links (+real -l/--links)

Adds symlink-target transmission (File is_symlink+symlink_target, STATUS_SYMLINK
frame, chunk type 2), munge-links sender containment + receiver-side symmetric
target containment, keep-dirlinks confined dir-symlink following (O_NOFOLLOW
realpath-rechecked), and fixes -l to copy symlinks as symlinks. munge_links +
keep_dirlinks cross the wire; copy_dirlinks client-only. PROTOCOL_VERSION
2.12.0->2.13.0. Review fixes: receiver rejects absolute/.. targets, gated unmunge,
-K O_NOFOLLOW+re-fstat, keep_dirlinks set once at config-accept, rel_buf overflow
fails the walk.

src/client/client_send.c

@@ -102,6 +102,8 @@ static bool prepare_scanner(const Config* config, int num_threads, PreparedScann
   options->copy_links = config->copy_links;
   options->safe_links = config->safe_links;
   options->copy_unsafe_links = config->copy_unsafe_links;
+  options->copy_dirlinks = config->copy_dirlinks;
+  options->munge_links = config->munge_links;
   options->checksum = config->checksum;
   options->one_file_system = config->one_file_system;
   options->file_list = (const FileListSet*)config->files_from_set;
@@ -1067,6 +1069,20 @@ static bool send_directory_entry(Client* client, File* file) {
   return send_str(client->file_descriptor, file_wire_path(file));
 }
 
+/* Transmit one symlink entry: a STATUS_SYMLINK frame carrying the destination
+ * path, the (sender-munged, if --munge-links) target string, and metadata when
+ * negotiated.  The receiver unmunges the target and creates the symlink beneath
+ * its root.  Symlinks never need an incremental check or data payload. */
+static bool send_symlink_entry(const Client* client, File* file, const Config* config) {
+  if (!file || !file_wire_path(file) || !file->symlink_target)
+    return false;
+  int fd = client->file_descriptor;
+  if (!send_status(fd, STATUS_SYMLINK) || !send_str(fd, file_wire_path(file)) ||
+      !send_str(fd, file->symlink_target))
+    return false;
+  return !config->use_metadata || metadata_send(fd, file->metadata);
+}
+
 // Send a single file directly via sendfile (non-incremental path).
 static bool send_file_direct_sendfile(File* file, int fd, bool use_metadata, const Config* config) {
   if (!send_status(fd, STATUS_NEXT))
@@ -1248,6 +1264,13 @@ static int send_chunk_with_removal(Client* client, Chunk* chunk, Config* config,
       change_emit_file_sent(config, f);
       continue;
     }
+    /* Symlink entry (-l / -k keep-as-symlink): only the target rides the wire. */
+    if (f->is_symlink) {
+      if (!send_symlink_entry(client, f, config))
+        return -1;
+      change_emit_file_sent(config, f);
+      continue;
+    }
     bool stream = f->data->data == NULL && f->data->size > 0;
     bool use_sendfile =
         (config->use_sendfile && !config->use_compression) || (stream && !config->use_compression);