feat(v4.0.0): BASE, DECIMAL, HEX, OCTAL and HLD

BASE and HLD leave their variable's word address; DECIMAL, HEX and
OCTAL store 10, 16 and 8.  Executed on the golden model at both cell
widths, including a recorded transcript of the v3 binary.

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

docs/v4.0.0/DECOMPOSITION.md

@@ -147,7 +147,7 @@ IF body1 ELSE body2 THEN →  if L1  drop body1  jump L2
 times, as on the F18. `FOR ... UNEXT` is the same but the body must fit in one instruction word.
 
 **Register conventions.** `A` and `B` are caller-saved. A word that uses them says so. Words in this
-document that clobber `A`: `@ ! +! -! 2@ 2! C@ C! UM* * UM/MOD Q.FROM-INT Q.TO-INT Q.* Q./ Q.EXP Q.SQRT Q.LOG Q.SIN Q.COS HOLD SIGN # #S . .R U. U.R D. D.R ? DUMP Q.PRINT TYPE SEND RECV`. Words that clobber `B`:
+document that clobber `A`: `@ ! +! -! 2@ 2! C@ C! DECIMAL HEX OCTAL UM* * UM/MOD Q.FROM-INT Q.TO-INT Q.* Q./ Q.EXP Q.SQRT Q.LOG Q.SIN Q.COS HOLD SIGN # #S . .R U. U.R D. D.R ? DUMP Q.PRINT TYPE SEND RECV`. Words that clobber `B`:
 `Q./ Q.EXP Q.SQRT Q.LOG Q.SIN Q.COS <# HOLD SIGN # #S #> . .R U. U.R D. D.R ? DUMP Q.PRINT EMIT CR SPACE SPACES TYPE SEND RECV`.
 
 **Return-stack words** (`>R R> R@ 2>R 2R> 2R@ I J UNLOOP` and the loop runtimes) are always IN.
@@ -453,15 +453,15 @@ All output reaches the console through `EMIT` (DEV).
 | Word | Fate | Notes |
 | --- | --- | --- |
 | `<#` `#` `#S` `HOLD` `SIGN` `#>` | CAP | Pictured output over `UM/MOD` and a 64-byte hold buffer, filled backwards from its end `HEND` through the pointer `HLD`. Standard stack effects (v3 took its double low cell on top, and its tolerant `#>` popped `ud` only if present; neither is kept). Otherwise v3's behaviour: digits `0`–`9` then `A`–`Z`; `BASE` outside 2–36 reads as 10; 63 characters; `HOLD` of a value outside 0–255 or into a full buffer stores nothing and sets `NODE-ERROR` (D-13). Definitions below. Executed on the golden model (2026-10-03) against a C reference in bases 2, 3, 8, 10, 16, 36 and four invalid ones. `<# #S #>` leaves its caller 4 data cells and 3 return entries; the signed picture `dup push ABS 0 <# #S pop SIGN #>` leaves 2 return entries. `#`, `#S`, `HOLD` and `SIGN` clobber `A` and `B`. |
-| `HLD` | CAP | Variable: byte address of the first held character. |
+| `HLD` | CAP | Variable: byte address of the first held character. `HLD ( -- addr )` is the variable's word address, a literal. Not a v3 word. Executed on the golden model (2026-10-03): after `<#` and each `HOLD` or `#`, `HLD @` is the address `#>` returns. |
 | `.` `.R` `U.` `U.R` `D.` `D.R` | CAP | Built on pictured output and `TYPE`; definitions below. As v3: the number in the current base, then one space; the `.R` words right-justify it in `width` columns first, print a wider number whole, and pad nothing for `width <= 0`. (The space after the `.R` words is not FORTH-79; it is what v3 prints.) Where v4 parts from v3: a double is `( lo hi )`, where v3's `D.` took the low cell on top; `D.` prints the whole double, where v3 printed `DOUBLE-OVERFLOW` unless it fitted one signed cell (they agree whenever it does); printing honours the `BASE` variable, where v3 printed in a host copy that only `DECIMAL`, `HEX` and `OCTAL` set, so `n BASE !` changed v3's input base but not its output; and the number is built in the 63-character hold buffer, so a longer one — a 64-bit cell in base 2, a large double in a small base — loses its leading characters and sets `NODE-ERROR` (D-13), where v3 printed from a private 80-character buffer. Executed on the golden model (2026-10-03) against a C reference in the ten bases of the pictured-output test and eleven field widths, and against five transcripts of the v3 binary (a sixth, the extreme cells, at 64-bit cells). Each leaves its caller 4 data cells and 2 return entries. All clobber `A` and `B`. |
 | `(W)` | CAP | Variable: the field width of the `.R` words. Like `BASE` and `HLD`, it lives in node memory, so the width is on neither stack while the picture runs. |
 | `.S` | RET | No visible stack pointer (D-2). |
 | `?` | CAP | `( addr -- )`: `a! @  jump .` — the cell at word address `addr` (D-1), printed as `.` prints it. Executed on the golden model (2026-10-03), including a transcript of the v3 binary. Leaves its caller 4 data cells and 2 return entries. Clobbers `A` and `B`. |
 | `DUMP` | CAP | `( baddr u -- )`: `u` bytes from byte address `baddr`, sixteen to a line, in v3's format: the address in hex, `": "`, each byte as two hex digits and a space (three spaces where the line runs out), `" \|"`, the bytes as characters with `.` for anything outside 32–126, `"\|"` and a new line. Always hex, whatever `BASE` is, and `BASE` is put back. The address is two hex digits per byte of a cell — 8 at 32-bit cells, 16 at 64, which is v3's width. Nothing for `u = 0`; for `u < 0` nothing is printed and `NODE-ERROR` is set, as `TYPE` does, where v3 raised its error flag. Addresses are not range-checked (open, `node.h`). Definition below. Executed on the golden model (2026-10-03) against a C reference at six alignments and every length 0–50, and at 64-bit cells against a transcript of the v3 binary, byte for byte. Leaves its caller 4 data cells and 2 return entries. Clobbers `A` and `B`. |
 | `(DP)` | CAP | Variable, 4 cells: `DUMP`'s saved `BASE`, address, count and column. |
-| `BASE` | CAP | Variable. |
-| `DECIMAL` `HEX` `OCTAL` | CAP | `10 BASE !` and so on. |
+| `BASE` | CAP | Variable. `BASE ( -- addr )` is its word address (D-1), a literal. Executed on the golden model (2026-10-03). Storing to it changes what is printed, which it did not in v3 (see `.`). |
+| `DECIMAL` `HEX` `OCTAL` | CAP | `10 BASE !`, `16 BASE !`, `8 BASE !`, with `!` in line as `a! !`. Executed on the golden model (2026-10-03), including a transcript of the v3 binary. Each leaves its caller 8 data cells and 8 return entries. Clobber `A`. |
 
 ```forth
 \ pictured output.  HEND is the byte address just past the hold buffer.