Draw the + on the pixel grid so it stays sharp on 1x screens

On a 1x display TDesign's + smeared at every small size: its 24-grid
strokes are centred on the box's middle, which at 12 or 14px is a pixel
boundary, so each ~1px bar covered two pixels at half ink. A thinner
stroke alone keeps the bar on the boundary. This is not Electrobun:
headless Chrome renders the same.

pixelAdd (icons.ts) redraws the + on the 14px grid with 1px bars at 7.5,
so they fill whole pixels at 1x and 2x, half a pixel off-centre. It
replaces tdesignAdd in the tab bar, the shortcut rows, the connection
manager and the tab menu. Checked at 1x in the real tab-bar and
shortcut-row markup: single-pixel bars at full ink.

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

docs/architecture.md

@@ -372,8 +372,9 @@ component; tokens → `ui/src/styles.css`.
   walker check the flag themselves.
 - `file-icons.ts` — extension → category map driving glyphs, colors
   (fixed `--icon-*` tokens from Oxide's hue scales) and the Kind column.
-- `icons.ts` — the one icon registry (TDesign, `@ng-icons/tdesign-icons`), passed to
-  `provideIcons` in `app.config.ts`. Icon names are plain strings in templates and
+- `icons.ts` — the one icon registry (TDesign, `@ng-icons/tdesign-icons`, plus one
+  redrawn glyph: `pixelAdd`, TDesign's + on the 14px pixel grid so it stays sharp
+  on 1x screens), passed to `provideIcons` in `app.config.ts`. Icon names are plain strings in templates and
   the build never checks them: an unregistered name renders nothing (console error
   only), so every name used anywhere must be listed here.
 - `platform.ts` — preload-global readers (`PLATFORM`, `APP_MODE`,

docs/gotchas.md

@@ -82,6 +82,14 @@ touching the adjacent code.
   it. Per-template picks had drifted to 12 sizes, and neighbours stopped
   matching: a 14.4px cog beside a 12.8px +, and a 12px + beside 9.6px × in
   the shortcut chips.
+- **On a 1x screen, a TDesign line through the icon's centre smears at any
+  small size.** At 12 or 14px the centre is a pixel boundary, so a ~1px bar
+  covers two pixels at half ink. A 1px stroke alone doesn't help, because the
+  bar stays centred on the boundary. This is geometry, not Electrobun:
+  headless Chrome renders the same. So the + is `pixelAdd` (`icons.ts`),
+  redrawn on the 14px grid with 1px bars at 7.5, which fill whole pixels at 1x
+  and at 2x. It's tuned for `--icon-size-sm` only. Arrow shafts (↑ →) have
+  the same issue if it ever shows.
 
 ## The interface scale (root font-size lever)