One home per fact: cut the copied rationale, and give the seam test room to mean something

AGENTS.md

@@ -293,10 +293,8 @@ Revisit only if the stated reason stops holding.
   takes that height with **`.scroll-region`** and carries the flex chain down to it, because only the
   page knows its own tree. The shell must never go looking through a page for a component it
   recognises — a rule keyed on `.table-wrap` works for a table the content slot holds directly and
-  silently clips one nested any deeper. `data-table` takes `scrollRegion: true` for exactly this, since
+  silently clips one nested any deeper. `data-table` takes `scrollRegion: true` for
-  its wrapper is host markup a page cannot put the class on itself. The `visual.spec.ts` scroll test presses **End** rather than sending a
+  exactly this, since its wrapper is host markup a page cannot put the class on itself.
-  wheel event (Firefox's synthetic wheel does not reach the document) and rather than
-  `scrollIntoView`, which a script can apply to an overflow-hidden box that no reader can scroll.
 - **`ICON_NAMES` (`src/ui/icons.ts`) is a host-owned registry, not a frozen plugin contract**, so it
   is deliberately not re-exported from `@plainpages/plugin-api`. The palette may narrow when the last reference
   to an id goes, and a plugin needing one gets it re-registered in the same change. Accepted cost: an

CHANGELOG.md

@@ -34,11 +34,13 @@ clip one nested any deeper. `data-table` takes `scrollRegion: true`, which puts
 ### Upgrading a plugin
 
 1. Set `apiVersion: "0.4.0"`.
-2. A page that scrolled the whole window needs no change — it now scrolls the document.
+2. A page that scrolled the whole window needs no change — it now scrolls the document. A
+   `data-table` on it keeps working, but its header stops sticking; see step 4.
 3. A page holding a region that filled the content column passes `fill: true` to the shell, puts
    `.scroll-region` on that region, and makes every wrapper between it and the content slot a flex
    column (`display: flex; flex-direction: column; flex: 1 1 auto; min-height: 0`). Miss a wrapper and
-   the region grows instead of scrolling, and `fill`'s bounded box clips it.
+   the region grows instead of scrolling, so the frame scrolls in its place — a second scrollbar is
+   the tell.
 4. A table whose header must stay put passes `scrollRegion: true` to `data-table` on such a page.
    `examples/plugins/scheduling` shows the whole chain on its shifts list.
 

e2e-tests/full-flow.spec.ts

@@ -205,7 +205,9 @@ test.describe.serial("authenticated admin journey", () => {
   // markup the shell does not own — so it is pinned here, on the reference plugin's own list, rather
   // than by asserting the class name the shell emits.
   test("plugin page: a filled page scrolls its table, not the document, and the header stays put", async () => {
-    await page.setViewportSize({ width: 1280, height: 300 });
+    // The region is the viewport less ~185px of chrome, so this leaves ~75px: enough that the 3-row
+    // fixture overflows it by half its height, and enough to hold the header a row scrolls under.
+    await page.setViewportSize({ width: 1280, height: 260 });
     await page.goto("/scheduling/shifts");
 
     const bounded = await page.evaluate(() => {
@@ -221,13 +223,19 @@ test.describe.serial("authenticated admin journey", () => {
     // Both halves, and both discriminating: miss a wrapper in the page's chain and the table grows
     // instead of scrolling, which pushes the frame past its own height.
     expect(bounded?.frameScrolls, "a filled page must fit its frame").toBe(false);
-    expect(bounded?.regionScrolls, "the table must be the thing that scrolls").toBe(true);
+    expect(bounded?.regionScrolls, "the fixture must overflow the region, or the rest proves nothing").toBe(true);
 
-    const headTop = async () => (await page.locator("thead th").first().boundingBox())?.y ?? -1;
+    const headTop = async () => {
+      const box = await page.locator("thead th").first().boundingBox();
+      expect(box, "the header must have a box to stay put").not.toBeNull();
+      return box?.y;
+    };
     const before = await headTop();
     await page.locator(".table-wrap").evaluate((el) => el.scrollTo(0, el.scrollHeight));
     await expect(page.locator("tbody tr").last()).toBeInViewport();
     expect(await headTop(), "the header sticks to a scrollport that moves").toBe(before);
+    // The journey shares one page; leaving it short would hand the next test a window it never chose.
+    await page.setViewportSize({ width: 1280, height: 800 });
   });
 
   test("plugin settings: the screen names the variable that sets each declared key", async () => {

e2e-tests/visual.spec.ts

@@ -52,13 +52,14 @@ for (const [name, path, tail] of [
       await expect(page.locator(".topbar")).toBeInViewport();
       if (width > 860) await expect(page.locator(".brand-name")).toBeInViewport();
 
-      // The open nav is a fixed overlay: the page must not slide out from under the scrim.
+      // The open nav is a fixed overlay, so a reader cannot scroll the page out from under the
+      // scrim. Focus can still move it, and stopping that needs script this page does not have.
       if (width <= 860) {
         await page.locator(".hamburger").click(); // the label is the control; the checkbox takes no pointer
         await expect(page.locator("#nav-toggle")).toBeChecked();
         const before = await page.evaluate(() => window.scrollY);
         await page.keyboard.press("Home");
-        expect(await page.evaluate(() => window.scrollY), "the page is locked while the nav is open").toBe(before);
+        expect(await page.evaluate(() => window.scrollY), "a key press cannot scroll the page while the nav is open").toBe(before);
       }
     });
   }

public/css/styles.css

@@ -112,7 +112,6 @@ html:has(#theme-light:checked) {
 
 /* ---------- 2. RESET ---------------------------------------- */
 *, *::before, *::after { box-sizing: border-box; }
-html, body { min-height: 100%; }
 body { margin: 0; background: var(--bg); color: var(--text);
   -webkit-font-smoothing: antialiased; }
 button { font: inherit; color: inherit; }
@@ -149,8 +148,7 @@ summary { list-style: none; cursor: pointer; }
 .ico-sm { width: 14px; height: 14px; }
 
 /* ---------- 3. APP GRID ------------------------------------- */
-/* Not a viewport-height box: the document scrolls, so a page is reachable below the fold without
+/* The document scrolls; `fill` opts out — see .app-fill (AGENTS.md → UI). */
-   bringing a scroll region of its own. `fill` opts out — see .app-fill (AGENTS.md → UI). */
 .app {
   display: grid;
   grid-template-columns: var(--nav-w) minmax(0, 1fr);
@@ -695,7 +693,7 @@ th[aria-sort="descending"] .sort-ico { transform: rotate(180deg); }
     background: rgba(0,0,0,.42);
   }
   .search { min-width: 150px; flex: 1 1 auto; }
-  /* The open nav is a fixed overlay: scrolling the page behind it moves what the scrim covers. */
+  /* The open nav is a fixed overlay: a reader scrolling would move what the scrim covers. */
   body:has(#nav-toggle:checked) { overflow: hidden; }
 }
 @media (max-width: 560px) {
@@ -730,16 +728,19 @@ th[aria-sort="descending"] .sort-ico { transform: rotate(180deg); }
 .app-bare { grid-template-columns: minmax(0, 1fr); }
 .app-bare .content { grid-column: 1; }
 
-/* `fill: true` on the shell: the viewport is the page, and a region inside it scrolls instead of the
+/* The shell's half of `fill: true` (AGENTS.md → UI). `auto`, not `hidden`: a page that misses a
-   document. For a page whose whole point is a bounded frame — a board of full-height columns, a table
+   wrapper in its own chain then scrolls here instead of losing the overflow. */
-   whose header must stay put. The height is the shell's to give: a page computing it would have to
-   know the topbar's own. What fills that height is the page's to say — `.scroll-region` below. */
 .app-fill { height: 100dvh; overflow: auto; }
 .app-fill .content { min-height: 0; }
 
-/* Marks the one element that takes the leftover height and scrolls. Every ancestor between it and
+/* The page's half: `min-height: 0` is the one everyone forgets, since `auto` floors a flex item at
-   `.content` has to be a flex column carrying this same pair, which is the page's own business —
+   its content. */
-   `min-height: 0` is the half everyone forgets, since `auto` floors a flex item at its content. */
 .scroll-region { flex: 1 1 auto; min-height: 0; overflow-y: auto; }
+
+@media print {
+  /* A bounded frame prints as one sheet otherwise, losing everything the region scrolls past. */
+  .app-fill { height: auto; overflow: visible; }
+  .scroll-region { overflow: visible; }
+}
 /* Auth/landing rendered inside the app shell: a roomy, centered column in the content area. */
 .shell-auth { flex: 1 1 auto; display: flex; justify-content: center; align-items: flex-start; padding: 40px 20px 80px; }

src/ui/data-table.test.ts

@@ -42,6 +42,8 @@ test("data-table renders sortable headers, row-select, typed cells, badges and k
   const html = flat(await render(config));
 
   assert.match(html, /<div class="table-wrap"><table class="table"><caption class="sr-only">People in the directory<\/caption>/);
+  // Opt-in, and only then: the class is what a filled page hands its leftover height to.
+  assert.match(flat(await render({ ...config, scrollRegion: true })), /<div class="table-wrap scroll-region">/);
 
   // Row-select: header select-all + per-row checkbox with a descriptive label.
   assert.match(html, /<th class="col-check" scope="col"><input type="checkbox" aria-label="Select all rows"><\/th>/);

src/ui/shell.test.ts

@@ -101,9 +101,8 @@ test("app shell can disable the menu: no sidebar, focused single-column layout",
 });
 
 test("app shell: fill is opt-in and composes with menu:false; what the class does is pinned in e2e", async () => {
-  // The opt-out from document scrolling is the shell's to give — a page cannot derive the height
+  // What the class does depends on the page's own flex chain (AGENTS.md → UI), so full-flow holds
-  // without knowing the topbar's own (AGENTS.md → UI). Its effect depends on the page's own flex
+  // that; this holds only that nothing opts a page in by accident.
-  // chain, so full-flow holds that; this holds only that nothing opts a page in by accident.
   const filled = await render({ fill: true, title: "Board", body: "<div>x</div>", nav: "" });
   assert.match(filled, /<div class="app app-fill">/);
   const bothOff = await render({ fill: true, menu: false, title: "Board", body: "<div>x</div>", nav: "" });