devices: --devices/--specials/-D/--copy-devices/--write-devices

Recreate char/block nodes via mknodat (privilege-gated, EPERM->warn+skip) and
FIFOs via mkfifoat; new STATUS_SPECIAL frame + validated rdev; sockets skipped;
-copy-devices copies st_size; -write-devices O_NOFOLLOW+O_NONBLOCK warn+skip.
preserve_specials/copy_devices/write_devices cross the wire. PROTOCOL_VERSION
2.12.0->2.13.0. Review fixes: -m source-removal keeps recreated specials, FIFO
ENXIO skip, rdev bounds at chunk_deserialize, STATUS_ERROR on receive branch,
scanner_prepare_special dedup.

src/shared/config.h

@@ -115,6 +115,22 @@ typedef struct Config {
   bool preserve_xattrs;
   bool preserve_devices;
   bool preserve_sparse;
+  /* Phase 4 special/devices: preserve special files (FIFOs, sockets) and device
+   * nodes on the destination by recreating them (mknod/mkfifo) instead of
+   * transferring content.  preserve_specials mirrors rsync --specials (the
+   * special-file half of -D); preserve_devices mirrors --devices (the device
+   * half of -D); both CROSS the wire so the receiver knows a special/device
+   * entry must be recreated rather than written as a regular file. */
+  bool preserve_specials;
+  /* --copy-devices: copy the CONTENT of a source device as an ordinary regular
+   * file on the destination (rsync's non-privileged safe mode), instead of
+   * recreating the device node.  CROSSES the wire (receiver treats the entry as
+   * a regular file, which is the default, so this is belt-and-braces). */
+  bool copy_devices;
+  /* --write-devices: write the received data directly INTO an existing device
+   * node on the destination instead of creating a regular file.  Dangeroud;
+   * see RSYNC_COMPAT.md for the tight gating.  CROSSES the wire. */
+  bool write_devices;
 
   // Issue #122: Output/logging options
   bool itemize_changes;
@@ -312,7 +328,7 @@ typedef struct Config {
   bool open_noatime;
 } Config;
 
-#define PROTOCOL_VERSION "2.12.0"
+#define PROTOCOL_VERSION "2.13.0"
 #define DEFAULT_CHUNK_SIZE (10 * 1024 * 1024)
 /* Upper bound on total basis-dir entries (rsync caps --link-dest at 20). */
 #define MAX_BASIS_DIRS 64