feat(v4.0.0): CASE, ['], S", WORDS, FORGET and FENCE

- compile.v4: CASE OF ENDOF ENDCASE, as v3 (they nest; a word out of
  place is a control structure mismatch); ['] and [LITERAL].
- quit.v4: S" and its run-time word; at the prompt the text is copied to
  PAD.
- capsule/system.v4: WORDS and VLIST; FORGET (FORTH-79), which gives the
  space back and will not remove a word below FENCE -- the capsule's own
  words -- where v3's FORGET DUP succeeds.
- tests/test_host_quit.c: ten more transcripts of the v3 binary, and
  nesting, the fence and the listing.

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

docs/v4.0.0/DECOMPOSITION.md

@@ -179,7 +179,7 @@ definition below depends on one, it says so.
 | **D-15** | Division by zero in `/` `MOD` `/MOD` `*/` `*/MOD` `M/MOD` (ruled 2026-10-04). | **Guarded: the word reports it and the line ends.** Each of these words tests its divisor before anything else. If it is zero the word prints v3's message, its own name and `: Division by zero`, takes its operands off the stack as v3 does, ends any definition that was open, prints ` ERROR` and returns to the prompt, from however deep; its caller is not returned to. `M/MOD` says so too, where v3 printed ` ERROR` alone. Source in `v4/capsule/forth.v4`; executed on the golden model's host node (2026-10-04), including transcripts of the v3 binary. `Q./` keeps D-11 (saturate and flag). `UM/MOD` and `SM/REM` are internal and unguarded: their callers have checked. What a mesh node, with no console, does on a zero divisor comes with the mesh (step 2); §4's definitions, which the mesh-node tests execute, still leave it unspecified. |
 | **D-16** | Stack overflow and underflow; `DEPTH`, `PICK`, `ROLL` (ruled 2026-10-04; revises D-2). | **Guarded: a stack fault.** Each stack counts what it holds. Before every opcode the node checks that the stacks hold what the opcode takes — including a `T` or `S` it only reads — and have room for what it leaves. If not, the opcode does nothing and the node faults exactly as for a bad address (D-14), to that kind's handler: `Stack overflow`, `Stack underflow`, `Return stack overflow`, `Return stack underflow`, then ` ERROR` and the prompt. **Every fault, D-14's included, empties both stacks**: the handler does not return, and what a word stopped part-way has left on the data stack is of no use to its caller. (v3 keeps what the failing word had not taken, and names the word: `DROP: Stack underflow`.) The fault handler is a table of five words, one per kind, each a jump (`(FAULTS)` in `v4/capsule/quit.v4`). Two registers (§7) are all a programme sees of the stacks: `DSTACK-DEPTH` and `RSTACK-DEPTH` read as the depth, and a store to one empties that stack. There is still no stack pointer and no address for a stack cell, so `SP@` and `SP!` stay retired; `.S` waits for number output to reach the capsule. The sizes were unchanged by this ruling, 10 and 9 (D-17 then deepens the host node's): one more value, or one more level of call, is now an error message where it used to be silent corruption. Executed on the golden model (2026-10-04): `tests/test_exec.c` for every opcode at every depth of both stacks, `tests/test_host_quit.c` from the prompt. |
 | **D-17** | Stack sizes on the host node (2026-10-04, following D-16). | **32 values and 32 return entries on the host node; a mesh node keeps the F18's 10 and 9.** Once the stacks are counted (D-16) their size is a parameter of the node, like its memory, and the host node is the one that runs the interpreter and the compiler underneath the user's programme: at 10 and 9 the prompt left a programme about six values, and `/` could be used only four words deep. The mechanism is the same at both sizes — top registers over a ring — and so is every word's definition. v3's stacks are deeper still. In the golden model the sizes are `V4_DATA_RING` and `V4_RET_RING` (`stack.h`), set for the host-node tests in `v4/Makefile`. |
-| **D-18** | Every other error (ruled 2026-10-04: "guard all errors"). | **A word that finds an error raises it, and the line ends there.** The word takes its own arguments off the stack and stores an error code in `NODE-ERROR` (§7). On a node with a prompt that store is a trap, a sixth kind of fault beside D-14's and D-16's: nothing after it executes, the return stack is emptied, and the prompt prints the code's message, ends any definition that was open, prints ` ERROR` and waits for the next line. Unlike the other faults it leaves the data stack as the word left it. The codes: 1 `Negative count` (`CMOVE`, `TYPE`), 2 `Not a number` (`NUMBER`), 3 `Number too long` (`HOLD` into a full buffer), 4 `Not a character` (`HOLD`), 5 `Dictionary full` (`,` `C,` `ALLOT`, any defining word), 6 `Name missing` (a defining word with nothing after it), 7 `Control structure mismatch`, 8 `Control structures too deep`; −1 means the word printed its own message (`UNKNOWN WORD: 'xxx'`, `xxx: compile-only`). Before this ruling these set the flag and the line ran on to its end. v3 stops at once too; its messages name the word (`LOOP: missing DO`) where v4's name the fault. With the trap not attached `NODE-ERROR` is plain memory and the word returns, which is how the words are tested below the prompt. D-11, D-12 and D-13 said "set `NODE-ERROR`"; on a node with a prompt that now means this. Executed on the golden model (2026-10-04): `tests/test_exec.c`, `tests/test_host_quit.c`. |
+| **D-18** | Every other error (ruled 2026-10-04: "guard all errors"). | **A word that finds an error raises it, and the line ends there.** The word takes its own arguments off the stack and stores an error code in `NODE-ERROR` (§7). On a node with a prompt that store is a trap, a sixth kind of fault beside D-14's and D-16's: nothing after it executes, the return stack is emptied, and the prompt prints the code's message, ends any definition that was open, prints ` ERROR` and waits for the next line. Unlike the other faults it leaves the data stack as the word left it. The codes: 1 `Negative count` (`CMOVE`, `TYPE`), 2 `Not a number` (`NUMBER`), 3 `Number too long` (`HOLD` into a full buffer), 4 `Not a character` (`HOLD`), 5 `Dictionary full` (`,` `C,` `ALLOT`, any defining word), 6 `Name missing` (a defining word with nothing after it), 7 `Control structure mismatch`, 8 `Control structures too deep`, 9 `Shift count out of range`, 10 `Protected word`; −1 means the word printed its own message (`UNKNOWN WORD: 'xxx'`, `xxx: compile-only`). Before this ruling these set the flag and the line ran on to its end. v3 stops at once too; its messages name the word (`LOOP: missing DO`) where v4's name the fault. With the trap not attached `NODE-ERROR` is plain memory and the word returns, which is how the words are tested below the prompt. D-11, D-12 and D-13 said "set `NODE-ERROR`"; on a node with a prompt that now means this. Executed on the golden model (2026-10-04): `tests/test_exec.c`, `tests/test_host_quit.c`. |
 
 **Consequences of D-2 that every definition must respect.** The data stack holds 10 items and the
 return stack 9, and every `call`, `FOR`, `DO` loop frame and `push` uses return-stack slots. Nesting
@@ -582,7 +582,7 @@ width and print a flood of spaces.
 | `SPAN` `TIB` `>IN` `SOURCE` | CC | Interpreter state on the host node. `TIB` is the buffer's byte address and `>IN` and `SPAN` their variables' word addresses, all in line; `SOURCE ( -- baddr u )` is `TIB` and `SPAN @`, a negative `SPAN` read as 0. Executed on the golden model's host node (2026-10-04). |
 | `WORD` `ENCLOSE` | CC | Parser; source in `v4/capsule/input.v4`. `WORD ( c -- baddr )` is FORTH-79 (ruled 2026-10-04): characters are taken from `TIB` until the delimiter `c` or the end of the text, leading delimiters ignored, and stored as a counted string; the delimiter met (`c`, or a zero if the text ran out) is stored after them, uncounted; `>IN` is left just past it; with nothing left the count is 0. The count is a byte, so a word over 255 characters is cut to 255; the buffer is 257 bytes. v3's `WORD` skipped every delimiter after the word, always stored a zero, and cut at 62. `ENCLOSE ( baddr c -- baddr n1 n2 n3 )`, not a FORTH-79 word, works on a zero-terminated string as v3's. Executed on the golden model's host node (2026-10-04) against C, and `ENCLOSE` against values recorded from the v3 binary. `WORD` keeps what it works on in memory and has at most three cells of its own on the data stack: it leaves its caller 7 data cells and 6 return entries. `(PARSE) ( c -- baddr )` is `WORD` without the skipping of leading delimiters: the text starts at `>IN` and may be empty. It is what `."` and `ABORT"` use, so that `." "` is an empty string. |
 | `NUMBER` `CONVERT` | CC | FORTH-79, not v3 (ruled 2026-10-04); source in `v4/capsule/input.v4`. `CONVERT ( d1 baddr1 -- d2 baddr2 )` takes the characters from `baddr1 + 1` on as digits in the current `BASE`, in either case, accumulating each into the double after multiplying it by `BASE`, and stops at the first that is not one; the double is `( lo hi )`. v3's was base 10 only, started at `baddr1`, and took the double low cell on top. `NUMBER ( baddr -- d )` is the counted string as a signed double in the current `BASE`, with an optional leading minus; anything else gives 0 and sets `NODE-ERROR`. v3's returned `( n flag )` in base 10. Executed on the golden model's host node (2026-10-04) against C in eight bases, including a digit that carries out of the low cell. `NUMBER` leaves its caller 3 data cells and 2 return entries; the interpreter does not use it (it has a single-cell conversion of its own that needs far less of the stack). |
-| `S"` `(s")` `[']` | CC | Compiler words. |
+| `S"` `(S")` `[']` | CC | Source in `v4/capsule/quit.v4` and `compile.v4`. `S" text"` `( -- baddr u )`, as v3: in a definition the text is compiled after a call to `(S")`, as `."` compiles it, and `(S")` leaves its address and length and returns past it. At the prompt the text is copied to `PAD` and stays there until `PAD` is used again. `['] xxx` compiles `xxx`'s address as a literal. v3 also has `[LITERAL]`, another name for `LITERAL`. Executed on the golden model's host node (2026-10-04), including transcripts of the v3 binary. |
 | `LITERAL` `[LITERAL]` (placeholders) | RET | The working `LITERAL` is in §5.17. |
 
 ```forth
@@ -729,7 +729,8 @@ it, `xt + 1`; for any other word the parameter field is the code itself.
 | `COLD` `WARM` | CC |  |
 | `BYE` `REBOOT` | HERA |  |
 | `SAVE-SYSTEM` | HERA | Snapshot becomes a capsule-image request. |
-| `WORDS` `VLIST` `SEE` | CC |  |
+| `WORDS` `VLIST` | CC | Source in `v4/capsule/system.v4`. The names in the dictionary, the newest first, a blank after each, a new line whenever one has passed column 64; a definition under way is not shown. v3 prints a heading, eight names to a line and a total. Executed on the golden model's host node (2026-10-04). |
+| `SEE` | CC |  |
 | `PAGE` | DEV |  |
 | `79-STANDARD` | CC |  |
 
@@ -745,7 +746,7 @@ it, `xt + 1`; for any other word the parameter field is the code itself.
 | --- | --- | --- |
 | `:` `;` `EXIT` `IMMEDIATE` `STATE` `[` `]` `LITERAL` `COMPILE` `[COMPILE]` | CC | Source in `v4/capsule/compile.v4`, all to FORTH-79. `:` makes an entry and starts compiling; the word cannot be found until `;`, so a redefinition can use the old word. `;` lays the return, reveals the word and stops compiling. `LITERAL` compiles the number on the stack when compiling. `COMPILE xxx` lays code that compiles `xxx` when the word it is in runs; `[COMPILE] xxx` compiles `xxx` though it is immediate. Executed on the golden model's host node (2026-10-04) against results recorded from the v3 binary; v3's `COMPILE` does not work (`: C1 COMPILE DUP ; IMMEDIATE  : U3 C1 + ;` gives `DUP: Stack underflow`), reported, not fixed. |
 | `CREATE` `VARIABLE` `CONSTANT` `DOES>` | CC | FORTH-79. A data word's code is one instruction word, a call to its run-time routine, and its parameter field is the cell after it: `(DOVAR)` is `pop ;` (the call's return address is the parameter field's address) and `(DOCON)` is `pop a! @ ;`. `VARIABLE` allots one cell, set to 0. `DOES>` lays a call to `(DOES)` and then `pop`: `(DOES)`, run by the defining word, rewrites the newest entry's code into a call to the code after it and returns from the defining word; that code's `pop` fetches the parameter field address. Executed on the golden model's host node (2026-10-04) against results recorded from the v3 binary. |
-| `FORGET` `FENCE` | CC |  |
+| `FORGET` `FENCE` | CC | Source in `v4/capsule/system.v4`. `FORGET xxx` is FORTH-79: `xxx` and every word defined after it are removed and their space is free again. A word that is not there is an error (`UNKNOWN WORD`), and so is one that starts below the address in the variable `FENCE` — where the capsule's own words are — which is D-18's code 10, `Protected word`. v3's `FORGET DUP` succeeds and takes `FORGET` itself with it. Executed on the golden model's host node (2026-10-04), including a transcript of the v3 binary. |
 | `LIT` | OP | `@p` |
 | `does_rt` | RET | Internal helper; `DOES>` is implemented by the compiler capsule. |
 
@@ -757,7 +758,7 @@ call would bury what it works on. A **compile-only** word may not be executed by
 `v4/capsule/forth.v4` holds the first words of the vocabulary flagged this way (`DUP`, `+`, `>R`, `I`,
 `LEAVE`, `@`, the in-line variables and so on).
 
-**The vocabulary at the prompt.** The host node's capsule is `v4/capsule/`, loaded in this order: `core.v4` (bytes, console, strings the rest rest on), `input.v4`, `dict.v4`, `codegen.v4`, `compile.v4`, `quit.v4` (the prompt, faults and errors), `forth.v4` (stack, arithmetic, division, `DEPTH` `PICK` `ROLL`), `numout.v4` (number output, `.S`) and `words.v4` (the stack, comparison, shift, double, mixed and string words of §5.1–5.9: `2SWAP 2OVER 2ROT 2>R 2R> 2R@ 2@ 2! -! 0<> 0> <> <= >= U< U> ABS MAX MIN WITHIN LSHIFT RSHIFT D- DABS D0= D0< D= D2* D2/ D< DMAX DMIN M+ M- CMOVE> MOVE FILL ERASE BLANK -TRAILING COMPARE SEARCH SCAN SKIP ?TERMINAL TRUE FALSE INVERT NOP`). Each is the definition this document gives; `tests/test_host_quit.c` runs them from the prompt against transcripts of the v3 binary. As v3, `LSHIFT` and `RSHIFT` with a count that is negative or as large as the cell is wide are an error (D-18, code 9, `Shift count out of range`). `M+`, like `M-` and `M/MOD`, takes its double in the standard order, low cell first; v3 takes it low cell on top.
+**The vocabulary at the prompt.** The host node's capsule is `v4/capsule/`, loaded in this order: `core.v4` (bytes, console, strings the rest rest on), `input.v4`, `dict.v4`, `codegen.v4`, `compile.v4`, `quit.v4` (the prompt, faults and errors), `forth.v4` (stack, arithmetic, division, `DEPTH` `PICK` `ROLL`), `numout.v4` (number output, `.S`), `system.v4` (`WORDS`, `FORGET`) and `words.v4` (the stack, comparison, shift, double, mixed and string words of §5.1–5.9: `2SWAP 2OVER 2ROT 2>R 2R> 2R@ 2@ 2! -! 0<> 0> <> <= >= U< U> ABS MAX MIN WITHIN LSHIFT RSHIFT D- DABS D0= D0< D= D2* D2/ D< DMAX DMIN M+ M- CMOVE> MOVE FILL ERASE BLANK -TRAILING COMPARE SEARCH SCAN SKIP ?TERMINAL TRUE FALSE INVERT NOP`). Each is the definition this document gives; `tests/test_host_quit.c` runs them from the prompt against transcripts of the v3 binary. As v3, `LSHIFT` and `RSHIFT` with a count that is negative or as large as the cell is wide are an error (D-18, code 9, `Shift count out of range`). `M+`, like `M-` and `M/MOD`, takes its double in the standard order, low cell first; v3 takes it low cell on top.
 
 **The stacks and the compiler.** The interpreter and compiler run on the same stacks as the user's
 words, with the user's values beneath them. The capsule was written for stacks of ten cells and nine
@@ -811,7 +812,7 @@ lays down was then run.
 | --- | --- | --- |
 | `IF` `ELSE` `THEN` `BEGIN` `UNTIL` `AGAIN` `WHILE` `REPEAT` `DO` `?DO` `LOOP` `+LOOP` | CC | Compile-time structure words, immediate and compile-only; source in `v4/capsule/compile.v4`. Expansions per §2 and below. What an opening word leaves for the word that closes it goes on a **control-flow stack in memory** (32 cells), not on the data stack, with a number saying which word left it; a closing word that finds the wrong number, or nothing, abandons the line. A loop that tests at its end (`UNTIL`) must drop the flag on both ways out, so `BEGIN` lays `jump L0  Ld: drop  L0:` and `UNTIL` lays `if Ld  drop`. Executed on the golden model's host node (2026-10-04): the code laid down for each is word for word what the text assembler makes of the expansion given here, and the programmes run give what the v3 binary gave. |
 | `LEAVE` `I` `J` `UNLOOP` | CC | In-line words (below), compile-only. |
-| `CASE` `OF` `ENDOF` `ENDCASE` | CC |  |
+| `CASE` `OF` `ENDOF` `ENDCASE` | CC | Source in `v4/capsule/compile.v4`; not FORTH-79, as v3. The value chosen on stays on the stack through the clauses. Each `x OF a ENDOF` is laid as `over xor if M  drop jump N   M: drop drop  a  jump END   N:`, and `ENDCASE` lays the `drop` that the part after the last `ENDOF` leaves the value for, with `END` after it. The control-flow stack holds the jumps to `END`, how many there are, and the tag 7; inside a clause, the jump to `N` and 8. They nest, and a word out of place is a `Control structure mismatch`. Executed on the golden model's host node (2026-10-04), including transcripts of the v3 binary. |
 | `EXIT` | OP | `;` |
 | `(BRANCH)` | OP | `jump` |
 | `(0BRANCH)` | IN | `if L … drop` (§2) — executed on the golden model (2026-10-03) as `IF 1 ELSE 2 THEN`, including results recorded from the v3 binary. |