Bring the tutorials back in line with the fixed interpreter

Eleven of the thirteen defects these two games found are fixed, and the
chapters that taught around them said things that are no longer true.

Chapter 17: the drawing verbs are no longer invisible, they are covered by a
text layer that `WINDOW` can now shrink; the cell size is `RGR(3)` and the grid
is `RWINDOW`, not a hand-measured constant; a character written past a short
row's end lands. Chapter 18: traps 3 and 4 -- the skipped block that broke its
caller's `RETURN`, and `SSHAPE` ignoring a subscript -- become history rather
than warnings, and Step 3 no longer claims a sprite is the *only* way to put a
picture up, only the one that costs nothing.

**Neither `.bas` listing changes, and both READMEs now say why.** The character
game still writes `CW# = 16` and the artwork game still keeps six brick stamps
in six scalars. What those listings are worth is being what a program written
against those constraints looks like, with comments explaining what each one was
avoiding -- rewriting them to pretend the problems never existed would throw
that away. So Chapter 17 Step 2 shows the `RGR(3)`/`RWINDOW` form and says
plainly that the listing beside it does not use it. That is the one place in
either chapter where a quoted fragment is not verbatim from the game.

Also: the closing pointers now say which entries are struck and which stand, and
the budgets table in Chapter 18 notes that several of those budgets were tighter
when the game was written.

TODO.md section 9 item 3 is updated rather than struck: the `WINDOW` half is
fixed, the default text area owning the whole window is not, and whether that
default is right is a question rather than a defect.

Verified against the fixed interpreter: both games run 45 seconds on the SDL
frontend with no error line and the score climbing; both suites are green in
both configurations; `docs_examples` passes and `docs_screenshots --check`
re-renders all thirteen figures byte-identically; coverage is 95.0% of lines
against the 90 gate, with src/variable.c at 100%; and every other quoted
fragment still appears verbatim in the listing it came from.

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

TODO.md

@@ -2629,8 +2629,21 @@ reduced against `build/basic`, the stdio build, unless it says otherwise.
    `tests/structure_verbs.c`, which today only exercises blocks whose bodies are plain
    statements.
 
-3. **In the standalone SDL build, nothing the graphics verbs draw can ever be seen.** Not
+3. **In the standalone SDL build, nothing the graphics verbs draw can be seen unless the
-   "does not persist" — *never visible at all*, in any frame.
+   program shrinks the text area first.** **Half done.** The tee sink now forwards
+   `WINDOW` (§6 item 31), so `sink_window()` is reachable and a program *can* take rows
+   back from the text layer -- which is the half that made this unanswerable. What stands
+   is the default: the text area is the whole window, so a program that does not call
+   `WINDOW` still cannot see a drawing.
+
+   Whether that default is right is a real question rather than a defect, and it is
+   entangled with what no `WINDOW` call fixes -- the frontend never clears and SDL
+   double-buffers, so a drawing has to be re-issued every frame, and it has to fit inside
+   one batch to survive a capture (item 5). Both are now documented in chapters 6, 13 and
+   14. **Sprites remain the only thing visible for free**, so the trick the game uses is
+   still the right one for a game; it should not be the *only* way, and it no longer is.
+
+   The original report, whose second bullet is fixed and whose first stands:
 
    ```basic
    GRAPHIC 1, 1

docs/17-tutorial-breakout.md

@@ -38,10 +38,11 @@ without your program doing anything:
 - the **sprites**, walked slot by slot after it.
 
 The drawing verbs are not one of them. `DRAW`, `BOX`, `CIRCLE` and `PAINT` go straight
-into the renderer's back buffer, and the text layer paints over the whole window on its
+into the renderer's back buffer, and **the text layer owns every row of the window by
-way past — so in the standalone SDL build **nothing you draw with them is ever visible**.
+default** — so it paints over anything they drew on its way past. `WINDOW` shrinks the
-That is recorded as a defect (`TODO.md` §9 item 3) rather than a design, but it is the
+text area and gives the rest of the window to the drawing verbs, but a drawing still has
-interpreter you have.
+to be re-issued every frame and has to fit in one batch to survive the capture; see
+[Chapter 13](13-differences.md#graphics).
 
 So this game uses no drawing verb at all. Anything that has to move smoothly is a sprite;
 anything that can live on a 16-pixel grid is text. Ball and paddle move; bricks, score
@@ -751,5 +752,6 @@ game against:
   differently from BASIC 7.0.
 - **[Chapter 14](14-architecture.md)** is the interpreter itself — the step loop, the
   pools and how to debug a program that stops for no visible reason.
-- `TODO.md` §6 and §9 carry the defects this game found, each with a reduction that fits
+- `TODO.md` §6 and §9 carry the thirteen defects these two games found, with the
-  on a screen and what a fix would touch.
+  reduction for each. Eleven have since been fixed and are struck; the entries are kept
+  because the reduction and the cause are worth more than the tidiness of deleting them.

docs/18-tutorial-breakout-artwork.md

@@ -100,15 +100,21 @@ broken while a gem is falling drops nothing.
 ## Step 3: Turn what you drew into a sprite
 
 In the standalone SDL build the text layer repaints every row of the window, opaque,
-after your program's steps have run and before the frame is presented — so **anything
+after your program's steps have run and before the frame is presented — so by default
-`DRAW`, `BOX` or `CIRCLE` puts on the screen is painted over before anybody sees it**.
+**anything `DRAW`, `BOX` or `CIRCLE` puts on the screen is painted over before anybody
-Sprites are drawn after the text layer. A sprite is the only thing on the screen a
+sees it**. Sprites are drawn after the text layer, which makes a sprite the one thing a
-program can rely on being visible. (`TODO.md` §9 item 3; the figures in this chapter are
+program can rely on being visible without doing anything else about it.
-rendered by a tool that omits the text layer, which is why they can show a drawing at
-all.)
 
-That leaves exactly one way to put a picture up: **draw it, capture it with `SSHAPE`,
+`WINDOW 0, 0, 49, 1` would hand the rest of the window to the drawing verbs. This program
-install the capture with `SPRSAV`.**
+does not, and would not want to: a drawing has to be re-issued every frame to survive
+double buffering *and* fit inside one 256-line batch to survive the capture, which is
+Step 4. A sprite has neither constraint — it is drawn from state the interpreter keeps.
+
+So: **draw it, capture it with `SSHAPE`, install the capture with `SPRSAV`.** Once it is
+a sprite it stays on the screen for nothing.
+
+(The figures in this chapter are rendered by a tool that draws no text layer, which is
+why they can show a bare drawing at all.)
 
 ```basic norun
 SSHAPE Z$, 0, 60, 800, 600
@@ -619,8 +625,12 @@ A silenced voice costs nothing to issue. One line beats eleven scattered through
 
 ## Five things in this dialect that do not do what they look like
 
-Each of these cost an evening. All five are filed in `TODO.md` §9 with a reduction and
+Each of these cost an evening, and each was filed in `TODO.md` §9 with a reduction and
-the file and line of the cause.
+the file and line of the cause. **Three of the five have since been fixed**, and are kept
+here as the history of why this program is shaped the way it is — a listing whose
+comments explain what it was avoiding is worth more than one quietly rewritten to pretend
+the problem never existed. The two that remain are the first and the last, and the first
+is the dangerous one.
 
 ### 1. The left operand decides integer or float arithmetic
 
@@ -787,6 +797,11 @@ and two four-note stings; one gem at a time; sticky and multiball share one offs
 balls stuck to the paddle sit on top of each other; and no high score on disk, because
 there is no disk.
 
+**Several of these budgets were tighter when this was written.** A scalar cost a pool
+slot, a saved shape could not live in an array, and a loop inside a skipped block leaked
+a scope — so a program had to spend variables to avoid all three. The listing has not
+been rewritten to take the room back, because what it does instead is show its working.
+
 ## Where to go next
 
 - **[Chapter 8](08-sprites.md)** is the sprite reference: every form of `SPRSAV`, the
@@ -796,5 +811,6 @@ there is no disk.
 - **[Chapter 7](07-sound.md)** is `SOUND`, `PLAY`, `ENVELOPE` and `VOL`.
 - **[Chapter 14](14-architecture.md)** explains the step loop and the pools this chapter
   keeps running into, from the interpreter's side.
-- `TODO.md` §9 is the eight defects this game found, each with a reduction, the cause and
+- `TODO.md` §9 is the eight defects this game found, each with a reduction and the cause.
-  what a fix would touch.
+  Six are fixed and struck; the two that stand are the left-operand rule, which is a
+  decision rather than a defect, and the batch tear, which is the host's to own.

examples/breakout/characters/README.md

@@ -39,9 +39,10 @@ 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. BASIC cannot ask —
+  C64_Pro_Mono at 16 points in the 800×600 window; the grid is 50×37. When this was
-  `WINDOW` knows, but the standalone frontend never offers it. Change the font or the
+  written BASIC had no way to ask. It has now — `RGR(3)`, `RGR(4)` and `RWINDOW`, added
-  window size and those two numbers have to change with them.
+  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.
 - **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.
@@ -56,8 +57,13 @@ a completely different program.
   game is silent rather than dead.
 - **No high score on disk.** There is no disk in this interpreter.
 
-The interpreter defects this game turned up are filed in `TODO.md` §6 item 30 and §9, each
+The interpreter defects this game turned up are filed in `TODO.md` §6 and §9, each with a
-with a reduction that fits on a screen.
+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.
 
 ## How this was checked
 

examples/breakout/sprites/README.md

@@ -68,9 +68,9 @@ Crediting Kenney is not required by CC0. It is here because it should be.
 Named honestly rather than left to be discovered:
 
 - **No music under the game**, only event sounds and two four-note stings. There is room in
-  the third voice for it; there is not much room anywhere else. 121 of the interpreter's
+  the third voice for it; there was not much room anywhere else when it was written. 121 of
-  128 variables are spoken for, four more are the ones it makes itself, and the label table
+  the interpreter's 128 variables are spoken for and the label table is at 61 of 64 —
-  is at 61 of 64.
+  several of them spent working around defects that have since been fixed.
 - **One gem at a time.** There is one sprite slot for it. A brick broken while a gem is
   falling drops nothing.
 - **Sticky and multiball share one offset.** Two balls stuck to the paddle at once sit on
@@ -82,5 +82,13 @@ Named honestly rather than left to be discovered:
 - **No high score on disk.** There is no disk.
 
 The eight interpreter defects this game turned up are filed in `TODO.md` §9, each with a
-reduction that fits on a screen, the file and line of the cause, and what a fix would
+reduction that fits on a screen and the file and line of the cause. **Six are now fixed**
-touch.
+— the leaking `DEF` call, the skipped block that broke its caller's `RETURN`, the ignored
+subscript on `SSHAPE`, `GRAPHIC CLR`, a negative `DATA` item, and half of the invisible
+drawing. The two that stand are the left-operand arithmetic rule, which turned out to be a
+decision rather than a defect and is now documented as one, and the 256-line batch tear,
+which belongs to the host.
+
+**The listing is unchanged**, and deliberately: it is what a program written against those
+constraints looks like, and its comments explain what it was working around. Six separate
+scalars for six brick stamps is no longer necessary, and it is still what the file does.