tty: the grid was 80x24 on a 160x50 screen, and wrapping was eager

Three symptoms, two causes, both in the terminal layer.

**The grid and TIOCGWINSZ disagreed about the size.** vt_init() sizes every
grid from gfx_cols()/gfx_rows(), and it runs at main.c:75 -- while the display
driver attaches its scanout from the PCI bus walk at main.c:99. So the grids
were the 80x24 fallback, and TIOCGWINSZ, which computed its own answer live,
said 160x50.

That one disagreement produced all three things visible in the report: text
stopped two thirds of the way down the screen, `ls` laid out 160 columns into
an 80-column grid so words split across the wrap ("vers" / "ion"), and zsh's
cursor tracking was wrong on every line.

Fixed in two places, because either alone would leave the trap set:
gfx_attach_scanout() now calls vt_resize(), so the grids learn the real screen
the moment there is one; and TIOCGWINSZ reports v->cols/v->rows rather than
measuring again. One number, from the terminal being asked.

**Wrapping was eager.** A glyph printed in the last column moved the cursor to
the next line immediately. Real terminals set a pending-wrap flag and wrap when
the *next* glyph arrives -- which is why a line exactly as wide as the screen
takes one row and not two, and why a program can write the bottom-right cell
without scrolling.

zsh's partial-line marker depends on that rule directly: it writes exactly
COLUMNS-1 spaces and expects to still be on the line. With eager wrap it left a
reverse-video '#' above every prompt, which is the hashtag in the report. Both
are gone.

Verified by screendump: `ls /proc` now fits one line with "version" intact, no
markers, and output fills the screen to the last row. schfs-check passes.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VQ7Qx8E1q1M1bbCq8QLHS2

docs/architecture/terminals.md

@@ -109,6 +109,30 @@ keyboard driver names it and stops.
 Input goes to whichever terminal is on screen. That is what makes a terminal a
 terminal: the keyboard follows the eyes.
 
+## Two rules that are easy to get wrong
+
+**The grid is the only source of truth for the size.** `TIOCGWINSZ` reports
+`v->cols`/`v->rows`, not a fresh `gfx_cols()`/`gfx_rows()`. When it computed
+its own answer there were two, and they disagreed: the grids are sized at
+`vt_init()`, which runs before the display driver is found on the PCI bus, so
+they were 80x24 while `TIOCGWINSZ` said 160x50. Text stopped two thirds of the
+way down the screen, `ls` formatted for a width the grid did not have and split
+words across the wrap, and zsh's cursor tracking was wrong on every line --
+three symptoms, one disagreement. `vt_resize()` now corrects the grids when a
+scanout arrives, and the ioctl reads them.
+
+**A glyph in the last column does not wrap.** It sets `wrap_pending`, and the
+wrap happens when the *next* glyph arrives. Every real terminal behaves this
+way and none of them document it clearly. Wrapping immediately makes a line
+exactly as wide as the screen take two rows instead of one, and makes it
+impossible to write the bottom-right cell without scrolling -- and zsh's
+partial-line marker depends on the rule directly: it writes exactly
+`COLUMNS - 1` spaces and expects the cursor to still be on that line. With
+immediate wrap, a reverse-video `#` appeared above every prompt.
+
+Anything that moves the cursor deliberately -- CR, LF, backspace, an escape
+sequence -- clears the debt.
+
 ## What it does not do
 
 - **No scrollback.** The grid is exactly the visible screen. Shift+PageUp does