Stop the listings and their chapters stating fixed defects as fact

You were right that this was still everywhere. The two `.bas` files carried
their workarounds as present-tense statements about the interpreter -- "a name
first created inside a GOSUB costs a value slot that is never handed back",
"writing PAST the terminator of a short row draws nothing at all", "SSHAPE and
GSHAPE ignore the subscript on a string array", "a FOR inside a BEGIN block does
not survive the RETURN" -- and every one of those is now false. A comment that
lies is worse than no comment, and these were the first thing anybody opening
the files would read.

**The characters game takes the geometry fix.** `CW# = 16` becomes `CW# =
RGR(3)`, and the grid comes from `RWINDOW`, so the game fits whatever window and
font the host gives it. That was the one thing in the listing that would break on
a different font, and `RGR(3)` and `RWINDOW` were added to the interpreter
because of it -- leaving the constant in place while Chapter 17 teaches the
function was the inconsistency worth closing. `RGR(1)` still comes first so a
build with no graphics device refuses by naming the device that is missing.

Everything else in both listings keeps its shape and says why. Declaring every
name up front, guarding loops with `GOTO`, six scalars for six brick stamps: none
is forced any more and none costs anything, so they stay, with the comments
marking which rules stand and which are history. The sprites header's five traps
are marked FIXED where they are fixed.

The chapters follow: Chapter 17 Step 2 no longer says "the listing still has
`CW# = 16`", and Chapter 18's trap section is "five things that did not do what
they looked like" with the two that still stand named up front rather than left
to be counted.

Verified: Chapter 17 Step 2's block is once again verbatim from the listing, so
every quoted fragment in both chapters matches its source with no exceptions;
both games run 40 seconds on the SDL frontend with no error line; both suites
green in both configurations; `docs_examples` and `docs_screenshots --check`
pass.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

examples/breakout/characters/README.md

@@ -8,8 +8,8 @@ messages are characters in the text grid.
 ../../../build-akgl/basic breakout.bas
 ```
 
-It needs the SDL build. The stdio build has no graphics device, so `RGR` refuses on the
-fourth line and the game stops there — which is exactly what it should do.
+It needs the SDL build. The stdio build has no graphics device, so the first `RGR` refuses
+and the game stops there — which is exactly what it should do.
 
 | Key | Does |
 |---|---|
@@ -38,11 +38,11 @@ a completely different program.
 
 ## Known warts, this game's own
 
-- **The cell size is a constant.** `CW#` and `CH#` are 16, measured with the bundled
-  C64_Pro_Mono at 16 points in the 800×600 window; the grid is 50×37. When this was
-  written BASIC had no way to ask. It has now — `RGR(3)`, `RGR(4)` and `RWINDOW`, added
-  because of this listing — and the listing has not been changed to use them, because
-  what it demonstrates is what a program does when the interpreter will not tell it.
+- **The cell size used to be a constant.** `CW#` and `CH#` were 16, measured by hand
+  against the bundled C64_Pro_Mono at 16 points, because BASIC had no way to ask — and it
+  was the one thing here that would break on a different font. `RGR(3)`, `RGR(4)` and
+  `RWINDOW` were added to the interpreter because of this listing, and it uses them now,
+  so the game fits whatever window and font the host gives it.
 - **Every character the game draws also goes to stdout**, because the frontend tees the
   text sink to the terminal. It made the whole game auditable from a log file during
   development and it is pure noise the rest of the time. Redirect it.
@@ -61,9 +61,12 @@ The interpreter defects this game turned up are filed in `TODO.md` §6 and §9,
 reduction that fits on a screen. Most are now fixed — the value pool that killed the first
 version after twenty-five seconds, the unreachable `WINDOW`, the character written past a
 short row — and the entries are struck rather than deleted, because the reduction is worth
-keeping. **The listing itself is unchanged**, and deliberately: it is what a program
-written against those constraints looks like, and its comments explain what it was
-working around.
+keeping.
+
+**The listing takes the geometry fix and leaves the rest of its shape alone.** Measuring
+the cell instead of assuming it makes the game strictly better, so it does. Declaring
+every name up front and looping with `GOTO` are no longer forced by anything, and are
+still what the file does — its comments now say which rules stand and which are history.
 
 ## How this was checked