feat(v4.0.0): every error is raised and ends the line (D-18)

Ruled 2026-10-04: guard all errors.  The errors that set NODE-ERROR and
let the line run on now stop it at once, with a message.

- A store of a non-zero code to NODE-ERROR is a trap, a sixth kind of
  fault: nothing after it executes, the return stack is emptied, and the
  data stack is left as the word left it.  Not attached, NODE-ERROR is
  plain memory, as the tests below the prompt use it.
- The capsule's words store a code where they stored -1, and the prompt's
  (RAISED) prints its message: Negative count, Not a number, Number too
  long, Not a character, Dictionary full, Name missing, Control structure
  mismatch, Control structures too deep.
- ' and COMPILE and [COMPILE] of a word that is not there say
  UNKNOWN WORD: 'xxx', as the interpreter does.
- tests: the trap in test_exec.c; every message from the prompt, with the
  rest of the line not run and the stack kept, in test_host_quit.c.

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

v4/capsule/compile.v4

@@ -35,6 +35,7 @@
 \           (C)+5 what a loop's end lays after its test
 \           (C)+6 (C)+7 a branch and a tag a control word is holding
 \           (C)+8 whether a data word's entry was made
+\           (C)+9 the error code a line is being abandoned with
 \   (CFP)   word address of the control-flow stack's pointer
 \   CFBASE CFEND   word addresses of its first cell and of the cell past its last
 
@@ -47,11 +48,15 @@ macro ROT   push SWAP pop SWAP   endmacro
 \ NODE-ERROR.  A definition that was under way stays hidden.  It returns to
 \ whatever called INTERPRET, which is QUIT (quit.v4): QUIT sees NODE-ERROR
 \ and prints ERROR.
-: (ABANDON)
+\ (ABANDON-AS) is the same with an error code (core.v4) for the prompt to
+\ print the message of.
+: (ABANDON-AS) ( code -- )
+  (C)+9 a! !
   0 STATE a! !  (CG-RESET)
   CFBASE (CFP) a! !
   SPAN a! @  >IN a! !
-  NODE-ERROR b! -1 !b ;
+  (C)+9 a! @  NODE-ERROR b! !b ;
+: (ABANDON)   -1 jump (ABANDON-AS)
 
 \ ---- the control-flow stack ----------------------------------------------------
 
@@ -59,7 +64,7 @@ macro ROT   push SWAP pop SWAP   endmacro
 : >CF
   (CFP) a! @  CFEND xor if FULL
   drop  (CFP) a! @  dup 1 + !  a! ! ;
-  FULL: drop drop  jump (ABANDON)
+  FULL: drop drop  8 jump (ABANDON-AS)       \ control structures too deep
 
 \ ( -- x )   pop; 0 from an empty stack, which no opening word leaves
 : CF>
@@ -153,10 +158,7 @@ header INTERPRET
        drop
        STATE a! @ if KEEP  drop (LIT,)  jump L
        KEEP: drop  jump L
-  BAD: drop drop                             \ "UNKNOWN WORD: '"
-       $4E4B4E55 (EMIT4) $204E574F (EMIT4) $44524F57 (EMIT4) $27203A (EMIT4)
-       (.WORD)  39 EMIT CR
-       jump (ABANDON)
+  BAD: drop drop  (UNKNOWN) drop  jump (ABANDON)
   EOL: drop drop ;
 
 \ ---- state ---------------------------------------------------------------------
@@ -206,13 +208,13 @@ header COMPILE immediate compile-only
 : COMPILE
   32 WORD (LOOKUP) if MISSING
   (LIT,)  &(COMPILE,) jump (CALL,)
-  MISSING: drop jump (ABANDON)
+  MISSING: drop  (UNKNOWN) drop  jump (ABANDON)
 
 \ [COMPILE] xxx   FORTH-79: compile xxx even though it is immediate
 header [COMPILE] immediate compile-only
 : BRACKET-COMPILE
   32 WORD (LOOKUP) if MISSING  jump (COMPILE,)
-  MISSING: drop jump (ABANDON)
+  MISSING: drop  (UNKNOWN) drop  jump (ABANDON)
 
 \ ---- data words ---------------------------------------------------------------------
 \ A data word's code is one call to its run-time routine; the call leaves the
@@ -267,7 +269,7 @@ header DOES> immediate compile-only
 \ ( tag wanted -- )   if they differ, abandon the line and leave the control
 \ word that called this as well: its return address is dropped, so the
 \ abandoning returns to the interpreter and nothing more is laid down.
-: (PAIR)   xor if OK  drop  pop drop  jump (ABANDON)   OK: drop ;
+: (PAIR)   xor if OK  drop  pop drop  7 jump (ABANDON-AS)   OK: drop ;
 
 \ ( ref -- )   the branch at ref lands here
 : (HERE!)   (FLUSH) HERE SWAP jump (RESOLVE)