docs: document transport split direction

REDESIGN.md

@@ -661,6 +661,130 @@ This keeps the future NetWare 4.x work aligned with the provider/process split:
 `nwdirectory`, `nwnds`, and `nwbind` may be separate processes or modules, but
 they should not be separate sources of truth for identity and directory data.
 
+## Transport split for future TCP/IP support
+
+Future TCP/IP support should be introduced as a transport code/library split,
+not as a new daemon.  The transport layer is below the NCP dispatcher: it owns
+wire IO, peer addressing, framing, and transport-specific discovery or watchdog
+behavior.  It does not own Bindery, Queue, Directory, File, Semaphore, or other
+NCP provider semantics.
+
+The intended source-level split is:
+
+```text
+src/nwtransport.c
+  common transport API and helpers
+  transport-neutral peer/session descriptors
+  dispatch to the selected transport implementation
+
+src/nwipx.c
+  existing IPX-specific implementation
+  ipxAddr_t conversion and compatibility helpers
+  IPX socket send/receive
+  SAP/RIP, IPX watchdog, and IPX broadcast behavior where applicable
+
+src/nwtcp.c
+  later TCP/IP implementation
+  TCP listener/session/framing code
+  IPv4/IPv6 peer address handling
+  no SAP/RIP assumptions
+
+src/nwconn.c
+  NCP session logic
+  request decode, dispatch handoff, reply construction
+  should gradually use transport-neutral peer/session data
+
+src/nwserv.c
+  process supervision and connection lifecycle
+  uses the transport layer for listener and peer management
+```
+
+These files should be linked into the existing `nwserv`/`nwconn` process model.
+`nwtransport` is a boundary in the code, not an `nwtransport` process.  Creating
+a separate transport daemon would add an IPC hop for every NCP packet, complicate
+disconnect/error handling, and make TCP stream ownership harder without adding a
+clear NetWare service boundary.
+
+The long-term direction is to remove raw IPX assumptions from higher layers.
+Today, the connection path still exposes `ipxAddr_t` in important places.  A
+future cleanup should introduce a transport-neutral peer descriptor, for
+example conceptually:
+
+```c
+typedef enum {
+  NW_TRANSPORT_IPX,
+  NW_TRANSPORT_TCP
+} NwTransportKind;
+
+typedef struct {
+  NwTransportKind kind;
+  union {
+    ipxAddr_t ipx;
+    struct {
+      unsigned char addr[16];
+      unsigned short port;
+      unsigned char family;
+    } tcp;
+  } u;
+} NwTransportPeer;
+```
+
+The exact structure should follow the existing mars-nwe style, but the ownership
+rule is the important part: NCP providers should not care whether a request came
+from IPX or TCP/IP.  They should see a connection/session and an NCP request,
+not a raw network address type.
+
+The transport API can start small.  Useful conceptual operations are:
+
+```c
+nwtransport_peer_equal();
+nwtransport_peer_to_string();
+nwtransport_recv();
+nwtransport_send();
+nwtransport_close_peer();
+nwtransport_peer_kind();
+```
+
+As with the NCP context design, these names are placeholders.  The first
+implementation can wrap the existing IPX behavior and leave TCP stubs out until
+there is a real TCP/IP target.  The goal is to stop new code from spreading
+`ipxAddr_t` into providers that should remain transport-independent.
+
+IPX-specific behavior must remain isolated.  SAP/RIP, IPX broadcast, and the
+existing IPX watchdog behavior are compatibility details of the IPX transport or
+its immediate `nwserv` integration.  TCP/IP should not be forced to emulate IPX
+SAP/RIP internally.  If TCP/IP later needs discovery or service advertisement,
+that should be designed as a TCP/IP-specific mechanism rather than hidden behind
+old IPX-only assumptions.
+
+The intended relationship is therefore:
+
+```text
+IPX client  -> nwipx  -> nwtransport -> nwconn -> NCP dispatcher -> providers
+TCP client  -> nwtcp  -> nwtransport -> nwconn -> NCP dispatcher -> providers
+```
+
+The provider/process rule still applies:
+
+```text
+Provider boundary does not imply process boundary.
+Transport boundary does not imply process boundary either.
+```
+
+Good future cleanup sequence:
+
+1. document the current IPX ownership in `nwserv.c` and `nwconn.c`;
+2. add `nwtransport.c`/transport headers as wrappers around existing IPX paths;
+3. move IPX-only helpers into `nwipx.c` without behavior changes;
+4. gradually replace raw `ipxAddr_t` use in session-neutral code with a
+   transport-neutral peer/session descriptor;
+5. keep NCP providers and the endpoint audit table transport-independent;
+6. add `nwtcp.c` only after the IPX wrapper boundary is stable.
+
+This keeps TCP/IP support compatible with the broader redesign: transport IO is
+separated from NCP semantics, but the existing `nwserv`/`nwconn` process model
+remains intact.
+
 ## Logging connection
 
 The dispatch redesign also supports the desired log cleanup.  If every request