TEXTURES.md: exercise grow_array (a second atlas layer opening) on tabs

Reasoned through but never watched happen, per the file's own "Not
separately stress-tested" note. Temporarily dropped PAGE from 1024 to
64 so tabs's ordinary mix of text sizes/families already exceeds one
page; a throwaway eprintln in grow_array confirmed two real grows in
one run (1->2, 2->4 layers), and run-headless.sh showed every tab's
text rendering correctly across layers, with no corruption. Both
temporary changes reverted; tabs and minimal confirmed byte-identical
to the pre-check screenshots afterward.

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

TEXTURES.md

@@ -450,14 +450,27 @@ list's ordering would have to be reconciled.
   "image span" tab exercises the same widget but needs a click to reach,
   which the headless compositor can't deliver (no seat devices, per I1's
   own note on this file) — the throwaway example is what stood in for it.
-- **Not separately stress-tested**: triggering a second atlas page (the
-  `grow_array` doubling-and-copy path) under a real glyph load large
-  enough to fill the first 1024x1024 page. The code path was reasoned
-  through and matches the existing single-page write exactly except for
-  the `z` origin and the extra copy, but nobody has watched a real
-  second-page grow happen on screen. Worth doing before trusting this
-  under a transcript with a large or unusual glyph set (many distinct
-  fonts/sizes, or a font with an unusually large character set).
+- **Exercised, 2026-09-04: `grow_array` under real load, on `tabs`.**
+  Rather than building a purpose-made glyph flood, `PAGE`
+  (`core/src/render/atlas.rs`) was temporarily dropped from 1024 to 64 —
+  small enough that `tabs`'s ordinary mix of sizes and families (nothing
+  exotic: a handful of `Text` widgets at a few sizes, one at
+  `Family::Monospace`) already exceeds one page's worth of distinct
+  glyphs. A one-line `eprintln!` in `grow_array` confirmed two real grows
+  in a single run (`GROW_ARRAY: 1 -> 2` then `GROW_ARRAY: 2 -> 4`, i.e.
+  glyphs landed on at least a third layer), and
+  `iris/run-headless.sh tabs --shot` showed every tab's text rendering
+  correctly with no corruption or missing glyphs — confirming the
+  `copy_texture_to_texture` grow-and-relocate path and cross-layer
+  sampling (`GlyphPrimitive.layer` addressing a layer beyond the first)
+  both work. Command:
+  `sed -i 's/PAGE: u32 = 1024/PAGE: u32 = 64/' core/src/render/atlas.rs`,
+  rebuild, `./run-headless.sh tabs --shot /tmp/x.png`, then
+  `git checkout -- core/src/render/atlas.rs` to revert — this is a
+  throwaway diagnostic value, never a committed change, since a real
+  1024px page holding only a handful of glyphs at a time would be mostly
+  wasted space in normal use. Confirmed the revert left `tabs` and
+  `minimal` byte-identical to the pre-check screenshots afterward.
 - **The decisive check**, `rigs/gpu-probe` rewritten to request iris's new
   (empty) feature/limit set and run on this checkout's own emulator
   (`ai-app-2`, via `emu`), booted with `EMU_GPU=software` so the guest gets