refactor: drop Config**, dead old-args plumbing, dedup constants, -Wformat-signedness

src/client/client_cli.c

@@ -3296,7 +3296,7 @@ int main(int argc, char* argv[]) {
       exit_code = 1;
     }
   } else if (config->use_multithreading) {
-    exit_code = send_files_multithreaded(&config);
+    exit_code = send_files_multithreaded(config);
   } else {
     exit_code = send_files(config);
   }

src/client/client_send.c

@@ -37,8 +37,6 @@
 #include <sys/stat.h>
 #include <unistd.h>
 
-#define STREAM_THRESHOLD (64ULL * 1024 * 1024)
-
 /* Aggregate loaded payload bytes the sender may buffer across the loader queue
    and the chunk in flight.  Sending one chunk adds up to ~2 * MAX_CHUNK_SIZE of
    transient serialize/compress buffers on top of the queued payloads, so this
@@ -1115,7 +1113,7 @@ static Client* connect_transfer_client(const Config* config) {
       return NULL;
     }
     return client_connect_ssh(config->ssh_destination, config->ssh_port,
-                              config->fastsync_server_path, config->old_args, config->rsh_command,
+                              config->fastsync_server_path, config->rsh_command,
                               config->blocking_io, config->remote_options,
                               config->remote_option_count);
   }
@@ -3617,10 +3615,9 @@ send_fail:
   return ret;
 }
 
-int send_files_multithreaded(Config** config_ptr) {
-  if (!config_ptr || !*config_ptr)
+int send_files_multithreaded(Config* config) {
+  if (!config)
     return 1;
-  Config* config = *config_ptr;
   if (config->list_only)
     return send_list_only(config);
   if (config->dry_run)

src/client/client_send.h

@@ -22,7 +22,7 @@ void client_set_abort_armed(bool armed);
  * never free it, and the caller retains ownership (freeing it with
  * config_delete() once the call returns). */
 int send_files(Config* config);
-int send_files_multithreaded(Config** config);
+int send_files_multithreaded(Config* config);
 /* rsync's --ignore-errors deletion gate: with no I/O error during the scan the
  * deletion phase always proceeds; with one it is suppressed unless
  * `--ignore-errors` was given.  Exposed so the decision can be unit-tested