fix(images): keep the discovery alert clear of the Rescan toast

A rescan that leaves the Images discovery alert visible could show its
fixed bottom toast over the alert on a short window. The concept's toast
keeps its placement; the production-only alert now scrolls into view only
as far as needed, with a 96px block-end scroll margin (D42).

TESTING.md

@@ -619,6 +619,13 @@ Recorded deviations on this page (spec §8):
   and no tag row. `positive_links` on `/__test__/concept/reset` links the newest
   images to their positive alone, so the inspector comparison sees the positive's
   category ("Positive prompt category: " hidden prefix, D21) and tag filters.
+- **D42**: the concept never shows a toast and a page alert together. Production keeps
+  the concept's fixed toast (centred, 22px from the bottom, 12px at 700px and below)
+  and, when an Import → Rescan toast leaves the Images discovery alert
+  (`.options-status`), scrolls that alert into view only as far as needed, with
+  `scroll-margin-block-end: 96px`, so it is never under the toast.
+  `Rescan toast does not cover the discovery alert it leaves` ends the window inside
+  the toast's band at 1600 and 390 pixels and measures both boxes.
 
 `tests/browser/inspector-concept.spec.mjs` compares the side panel and the viewer's
 full details (#249 D4) for alpine_00001.png, at 1600x1100 and 390x844 in both themes:

tests/browser/workspace-images.spec.mjs

@@ -1559,6 +1559,39 @@ test('unreachable sources and categories announce one error', async ({ page }) =
     await expect(page.getByRole('alert')).toHaveCount(0);
 });
 
+// PR D-b Task 3 (D42): the shared toast keeps the concept's fixed bottom placement, so a discovery alert that a rescan
+// leaves visible must not stay under it. The window ends just below the alert, inside the toast's band, as on a short
+// window or a phone with its browser bars shown.
+const boxOf = locator => locator.evaluate(node => {
+    const { top, right, bottom, left } = node.getBoundingClientRect();
+    return { top, right, bottom, left };
+});
+const overlaps = (a, b) => a.left < b.right && b.left < a.right && a.top < b.bottom && b.top < a.bottom;
+for (const width of [1600, 390]) {
+    test(`Rescan toast does not cover the discovery alert it leaves at ${width}px`, async ({ page }) => {
+        await page.setViewportSize({ width, height: 1100 });
+        await page.route('**/prompt_manager/library/options*', route => route.abort('failed'));
+        await page.goto(workspace);
+        await expect(cards(page)).toHaveCount(2);
+        const alert = page.getByRole('alert');
+        const failed = 'Categories could not be loaded. Rescan from Import to retry.';
+        await expect(alert).toHaveText(failed);
+        const toastInset = width > 700 ? 22 : 12;
+        await page.setViewportSize({ width, height: Math.ceil((await boxOf(alert)).bottom) + toastInset + 16 });
+        await rescan(page);
+        await expect(toast(page)).toHaveText(/^Rescan finished\. /);
+        await expect(alert).toHaveText(failed);
+        await expect.poll(async () => overlaps(await boxOf(alert), await boxOf(toast(page)))).toBe(false);
+        const [shown, placed] = [await boxOf(alert), await boxOf(toast(page))];
+        expect(shown.top).toBeGreaterThanOrEqual(0);
+        expect(shown.bottom).toBeLessThanOrEqual(placed.top);
+        // The concept's toast stays where the concept puts it: centred, its inset from the bottom.
+        const viewport = page.viewportSize();
+        expect(Math.round(viewport.height - placed.bottom)).toBe(toastInset);
+        expect(Math.abs((placed.left + placed.right) / 2 - viewport.width / 2)).toBeLessThan(1);
+    });
+}
+
 // #249 final review m8: D36's alphabetical categories hold whatever order the server sends.
 test('toolbar categories are alphabetical regardless of server order', async ({ page }) => {
     await page.route('**/prompt_manager/library/options*', route => route.fulfill({

web/js/workspace/images.mjs

@@ -638,15 +638,23 @@ export function mountImages(main, api, parentScope, {embedded = false, fetchPage
             if (scope.signal.aborted) return;
             renderLoadStatus();
             if (found) reset();
-            if (!scope.signal.aborted) showWorkspaceToast(rescanFinished(result));
+            if (!scope.signal.aborted) announceRescan(rescanFinished(result));
         } catch {
             // A failed rescan leaves the collection and any discovery alert as they were.
-            if (!scope.signal.aborted) showWorkspaceToast(RESCAN_FAILED);
+            if (!scope.signal.aborted) announceRescan(RESCAN_FAILED);
         } finally {
             rescanning = false;
             importDialog?.setRescanBusy(false);
         }
     }
+    /**
+     * D42: the concept's toast stays fixed at the bottom, so a discovery alert the rescan leaves is scrolled, only when
+     * it must be, clear of the toast's band (its `scroll-margin-block-end`).
+     */
+    function announceRescan(message) {
+        showWorkspaceToast(message);
+        if (!optionsStatus.hidden) optionsStatus.scrollIntoView({block:'nearest', inline:'nearest'});
+    }
     async function refreshInspectionCollection() {
         if (scope.signal.aborted) return;
         // Numeric roots may now name another source; retire the old stream first.

web/js/workspace/workspace.css

@@ -174,7 +174,9 @@ main:focus-visible { outline: 2px solid var(--ca-focus); outline-offset: 4px; }
 @container images-page (inline-size < 600px) {
     .image-workspace { grid-template-columns: minmax(0, 1fr); }
 }
-.options-status { font-size: 12px; padding-inline: 4px; }
+/* #249 D42: a discovery alert a rescan leaves scrolls clear of the concept's fixed toast (22px inset, 12px at 700px and
+   below, two 12px lines at 390px), never under it; the toast itself keeps the concept's placement. */
+.options-status { font-size: 12px; padding-inline: 4px; scroll-margin-block-end: 96px; /* D42 */ }
 /* Until their pages rebuild (PR E Library, PR F history): the Library's and the recorded run's prompt blocks keep
    their spacing, the Archive negative dialog keeps `section.prompt-block`, and the shared prompt sender keeps its
    dialog and send button. */