feat(v4.0.0): the prompt -- QUIT, ABORT, ABORT" and ."

Layer 5 of the compiler capsule.  The host node is now started at QUIT and
left running: it prompts, reads a line from its console with QUERY,
interprets it, says " ok" or " ERROR", and goes round again.

- capsule/quit.v4: QUIT and ABORT (FORTH-79), ABORT" and (ABORT") as v3 has
  them, ." and (.") (FORTH-79).  Text is compiled as a counted string after
  the call; the run-time word returns to the cell after it.
- INTERPRET prints v3's messages before abandoning a line:
  UNKNOWN WORD: 'xxx' and xxx: compile-only.
- core.v4: CR SPACE COUNT TYPE, as DECOMPOSITION.md gives them.
- input.v4: WORD split so that (PARSE) can take text without skipping
  leading delimiters (." " is an empty string); EXPECT keeps its place in
  memory, so six values may wait on the stack while a line is typed.
- tests/test_host_quit.c: the node is fed characters and its output read;
  16 sessions are transcripts of the v3 binary.

QUIT stops the line from inside any word and says nothing; v3's goes on
with the line and cannot be compiled.  v3's compiled ABORT" crashes.

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

v4/capsule/compile.v4

@@ -43,8 +43,9 @@ macro ROT   push SWAP pop SWAP   endmacro
 
 \ ( -- )   give up the line: stop compiling, forget the word being built and
 \ whatever control structures were open, skip the rest of the input, and set
-\ NODE-ERROR.  A definition that was under way stays hidden.  (QUIT will add
-\ the message and the stack reset.)
+\ 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)
   0 STATE a! !  (CG-RESET)
   CFBASE (CFP) a! !
@@ -92,6 +93,9 @@ macro ROT   push SWAP pop SWAP   endmacro
   dup -3 + a! @ 8 and if CALL  drop jump (INLINE,)
   CALL: drop jump (CALL,)
 
+\ ( -- )   print the word WORD has just left
+: (.WORD)   WBUF COUNT jump TYPE
+
 header EXECUTE
 : EXECUTE ( xt -- )   push ;
 
@@ -128,7 +132,8 @@ header EXECUTE
 \ A word in the dictionary is executed, or, when compiling and not immediate,
 \ compiled.  Anything else must be a number in the current BASE: it is left
 \ on the stack, or compiled as a literal.  What is neither, or a compile-only
-\ word met while interpreting, abandons the line.
+\ word met while interpreting, abandons the line, with v3's message:
+\   UNKNOWN WORD: 'xxx'          xxx: compile-only
 header INTERPRET
 : INTERPRET
   L: 32 WORD dup C@ if EOL
@@ -139,13 +144,18 @@ header INTERPRET
        drop EXECUTE  jump L
        COMP: drop (COMPILE,)  jump L
      INTERP: drop  16 and if RUN
-       drop drop  jump (ABANDON)
+       drop drop  (.WORD)                    \ ": compile-only"
+       $6F63203A (EMIT4) $6C69706D (EMIT4) $6E6F2D65 (EMIT4) $796C (EMIT4) CR
+       jump (ABANDON)
        RUN: drop EXECUTE  jump L
   NUM: drop  (NUM?) if BAD
        drop
        STATE a! @ if KEEP  drop (LIT,)  jump L
        KEEP: drop  jump L
-  BAD: drop drop  jump (ABANDON)
+  BAD: drop drop                             \ "UNKNOWN WORD: '"
+       $4E4B4E55 (EMIT4) $204E574F (EMIT4) $44524F57 (EMIT4) $27203A (EMIT4)
+       (.WORD)  39 EMIT CR
+       jump (ABANDON)
   EOL: drop drop ;
 
 \ ---- state ---------------------------------------------------------------------