Merge feat/p4-preallocate: --preallocate

# Conflicts:
#	tests/test_client_cli.c
#	tests/test_config.c

src/client/usage.c

@@ -182,6 +182,7 @@ void print_usage(void) {
   printf("  --copy-unsafe-links  Only transform unsafe symlinks into referent files\n");
   printf("  -S, --sparse        Handle sparse files efficiently\n");
   printf("  --inplace           Update files in-place (no temp+rename)\n");
+  printf("  --preallocate       Allocate destination file space up front (fail-fast on full disk)\n");
   printf("  --append            Resume a shorter destination by appending only its tail\n");
   printf("                    (prefix is not verified; requires --incremental)\n");
   printf("  --append-verify     Like --append, but verifies the retained prefix checksum\n");