docs: describe the derived cap and cite the coupling beads (improvise-felo.1)

Review of #307 at 7b9e868b: the duplicate-step evidence and argument still
said 12, tui.md bounded a collision tuple by twelve, and the coupling
inventory named no beads. The page-bar entry now notes its unclipped
set_string can overwrite the right border.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VdfEGXA7aJ6ftMsCc9PJze

context/code/core.md

@@ -598,40 +598,46 @@ fixture that fills to the cap either derives it or fills until
 **Degrades as categories grow.** These are not fixed here; each is a place
 where 24 is worse than 12. Most were already reachable at 12.
 
-- **The TUI row header is the sum of its levels.** In `src/ui/grid.rs`, around
+- **The TUI row header is the sum of its levels** (improvise-gtn7.5). In `src/ui/grid.rs`, around
   `row_header_width`/`data_area_width` (and
   `ui::viewport::compute_row_header_width`), each level takes 4 to 24 cells.
   Categories on Row therefore cost at least 4 cells each, and the data area
   saturates to zero width with no data drawn.
 - **Column headers take one line per level, but the keypress path does not
-  count them.** `App`'s `visible_rows` is `term_height − 8`, a fixed allowance
+  count them** (improvise-gtn7.6). `App`'s `visible_rows` is `term_height − 8`, a fixed allowance
   that ignores the column levels, the group row and the page bar. So with
   several categories on Column, the cursor can scroll below the drawn grid.
-- **The page bar is one unclipped line.** It is `GridWidget::render`'s
-  `page_coords` join. Default seating (`View::on_category_added`) sends every
+- **The page bar is one unclipped line** (improvise-gtn7.7). It is
+  `GridWidget::render`'s `page_coords` join, drawn with a bare `set_string`
+  that is not clipped to the inner rectangle, so a long bar can overwrite the
+  block's right border. Default seating (`View::on_category_added`) sends every
   regular category after the second to Page. A 24-category import therefore
   puts 22 selectors on one line, clips most of them without a mark, and opens
   on a single slice.
-- **Side panels do not scroll.** In `src/ui/panel.rs`, an item past
+- **Side panels do not scroll** (improvise-gtn7.8). In `src/ui/panel.rs`, an item past
   `item_height` is not drawn, and the cursor can move onto it unseen. The
   category panel lists every category plus its expanded items.
-- **The wizard's field list does not scroll.** Its `ReviewProposals` arm in
+- **The wizard's field list does not scroll** (improvise-8jk6.1). Its `ReviewProposals` arm in
   `src/ui/import_wizard_ui.rs` breaks at the popup's bottom (the popup is at
   most 30 rows high), unlike the steps that use `scrolling`. About 22 fields
   fit, so the over-the-cap case cannot show every field it asks the user to
   fix.
-- **Loading the store is O(k log k) per cell and O(cells × k) in memory.** It
+- **Loading the store is O(k log k) per cell and O(cells × k) in memory**
+  (improvise-felo.2). It
   measured 3× from 12 to 24 (the table above).
 - **A fit declines more columns.** `unaffordable_categories` drops the widest
   category columns once the encoding passes `MAX_FEATURES`. A wide document
   is fit on fewer of its categories, and the fit says so.
 - **`cross_product` is exponential in the categories placed on one axis**, and
   `prune_empty`'s `has_value` matrix is rows × columns. The cap never bounded
-  either.
+  either. Virtualizing the grid is improvise-felo.3.
 - **Header repeat suppression costs O(levels) per position and level**
   (`render.rs::shows`). That is O(rows × levels²) per frame, which is small at
   24.
 
+The records-mode build's quadratic (improvise-sk32) is not category coupling;
+it is listed above because this measurement found it.
+
 The browser adapts where the TUI does not. `#tiles` and `#categories` scroll,
 and `web/shell.js` charges each column level to the extent.
 

context/code/formula-and-io.md

@@ -736,14 +736,16 @@ is already a category. `suggested_duplicate_category` lives on the pipeline, so
 the CLI's `separate` uses the same rule.
 
 **At the category cap, Separate is shown and disabled.** The reported import
-already had 12 regular categories, which is `MAX_CATEGORIES`. Option (b) adds a
+had 12 regular categories, which was `MAX_CATEGORIES` when this was written.
+Option (b) adds a
 **regular** category, and the user declined a hidden virtual one. So at the cap
 the option is drawn "(unavailable)" with its reason and remedy: go back and
 Skip a column or make it a Measure, or choose Sum. The reason is decided in
 `ImportWizard::duplicate_options`, so every front end words it the same way.
-This is the conservative reading, and it is **an open question for the user**:
-lifting the cap for this one category, or counting it outside the cap, is a
-model-layer decision this ticket did not take.
+This was the conservative reading, and it left an open question for the user.
+**The user answered it on 2026-09-25 by raising the cap to 24**
+(improvise-felo.1), so "keep separate" is available for the reported import
+now. The option is still disabled for any import that fills the new cap.
 
 **Headless paths refuse by default.** `improvise import --no-wizard` has
 nobody to ask, so `--on-duplicate refuse|sum|separate` defaults to `refuse`.

context/code/tui.md

@@ -581,7 +581,7 @@ and the list can never scroll away. It is by item, not by line, because the
 wizard state cannot know the panel width that line-level clamping needs. The
 residual is honest. A **single** item taller than the whole list area, roughly
 1,500 characters at 80 columns, is still clipped at the panel's bottom. No
-wizard warning is that long today: a collision tuple is bounded by twelve
+wizard warning is that long today: a collision tuple is bounded by `MAX_CATEGORIES`
 categories plus labels, but a label value is not bounded.
 
 **Every write is clipped to the panel.** The widget draws through `Panel`,