feat(v4.0.0): a node finds the way -- routes, passing on, SEND; one fault stands

MESH.md step 4. Each node has a table of destinations and the port toward
each, and a port for everything else (ROUTE, DEFAULT-ROUTE, NO-ROUTES). A
message not for this node is passed on whole; one with nowhere to go is
dropped and counted. What text prints and how it ended go back to the node
it came from by the same table. SEND sends text to another node.

test_host_mesh.c: three StarForth nodes in a row behind a console, 28
checks at both widths and under ASan+UBSan. hosted-check on three ISAs.
Bare metal: logs/20261006-115225 (amd64), -115501 (aarch64), -115849
(riscv64).

NOT DONE. Two neighbours that write to each other at once wait for ever:
a write blocks until the neighbour reads, and a node that is writing is
not reading. The last check in test_host_mesh.c shows it (KNOWN FAULT).
MESH.md section 7a sets out the ways out; none is chosen.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

v4/capsule/core.v4

@@ -6,7 +6,8 @@
 \
 \ Constants the loader supplies:  N-1 (cell bits - 1), NODE-ERROR, CONSOLE-TX,
 \ CONSOLE-RX, CONSOLE-STATUS, BASE, (EMIT-HOOK), (MSG), (REPLY), (ME), (OUT),
-\ (OUT^).
+\ (OUT^), (CONSOLE), (ROUTES), (ROUTE#), (ROUTE-DEFAULT), (PRINT-TO),
+\ (PRINT-PORT).
 \
 \ ERRORS (D-18).  A word that finds an error takes its arguments off the stack
 \ and stores a code in NODE-ERROR.  On a node with a prompt that store is a
@@ -94,8 +95,9 @@ header CMOVE
 \ ---- section 5.10: the console -------------------------------------------
 \ ---- what a node prints (docs/v4.0.0/MESH.md section 6) ------------------------
 \ A node has no console of its own.  It does what a message asks, and what
-\ it prints while doing it goes back, as a message, to whoever sent that one,
-\ on the port it came on.  A message is seven words and then its text, four
+\ it prints while doing it is sent as a message: to the node in (CONSOLE), or
+\ if that is 0 to whoever sent the text; by the port that leads there, or if
+\ this node knows of none, by the port the text came on.  A message is seven words and then its text, four
 \ characters to a word:
 \     to, from, type, heat and TTL, ACL tag, sequence, length in characters
 \ The types:  1 text to be interpreted   2 what a node printed   3 how the
@@ -112,20 +114,35 @@ header CMOVE
 \ the character and A on the return stack while it works.  Sending needs
 \ two.
 
-\ ( type -- )   the first six words of a message to the sender of the one
-\ being served; its length, and its text, are the caller's to send.  Each
-\ write waits for the neighbour to take it.  B is left at the port.
+\ FINDING THE WAY (MESH.md section 7).  A node knows its ports and nothing of
+\ the shape they are wired in.  Whoever wires it tells it, for a node, which
+\ port leads toward that node: the table (ROUTES), (ROUTE#) entries of a
+\ node's number and a port's address; and (ROUTE-DEFAULT), the port for any
+\ node that is not in the table, or 0.
+
+\ ( node -- port | 0 )   the address of the port that leads toward the node
+: (PORT-FOR)
+  (ROUTE#) a! @ if NONE  -1 +  (ROUTES) a!
+  FOR  dup @+ xor if HIT  drop  @+ drop  NEXT
+  0
+  NONE: drop drop  (ROUTE-DEFAULT) a! @ ;
+  HIT: drop drop  @+  pop drop ;
+
+\ ( type -- )   words 1 to 5 of a message this node sends: from, type, and
+\ the three that are carried and not used yet.  Its caller has put B at the
+\ port and sent word 0, whom it is to, and sends the length and the text.
+\ Each write waits for the neighbour to take it.
 : (HDR)
-  (REPLY) a! @ b!
-  (MSG)+1 a! @ !b                        \ to
   (ME) a! @ !b                           \ from
   !b                                     \ type
-  0 !b  0 !b  0 !b ;                     \ heat and TTL, ACL tag, sequence: carried, not used yet
+  0 !b  0 !b  0 !b ;                     \ heat and TTL, ACL tag, sequence
 
-\ ( -- )   send what has been printed: its length, then its characters, four
-\ to a word, the first lowest
+\ ( -- )   send what has been printed, to where (PRINT-TO) says, by the port
+\ (PRINT-PORT): its length, then its characters, four to a word, the first
+\ lowest.  quit.v4 sets those two when text for this node arrives.
 : (FLUSH-OUT)
   (OUT^) a! @  (OUT) xor if NONE  drop
+  (PRINT-PORT) a! @ b!  (PRINT-TO) a! @ !b
   2 (HDR)
   (OUT^) a! @  (OUT) -  dup !b
   3 + 2/ 2/  -1 +  (OUT) a!