[AGILE-361] Bound row resolution to its own list

Selection resolved rows through the unbounded helper, which descends
into nested lists: a section row answered with the first field of the
list inside it. The rows container now bounds every lookup.

Author: myabc

frontend/src/stimulus/controllers/dynamic/sortable-lists.controller.spec.ts

@@ -321,6 +321,8 @@ describe('Sortable lists controller', () => {
       fieldList,
       firstFieldItem: fieldList.querySelector<HTMLElement>('[data-sortable-lists--item-id-value="cf1"]')!,
     };
+  }
+
   // Layered on renderFixture: same list/item/scrollable structure, plus the
   // selection-enabled value on the root and tabindex on every item. The
   // value is set at creation time, not via a later setAttribute — Stimulus
@@ -1276,6 +1278,8 @@ describe('Sortable lists controller', () => {
         expect.objectContaining({ method: 'PUT' }),
       );
     });
+  });
+
   // "Collapse a wider selection onto the dragged card" and "select the
   // dragged card" are different things; only the first is in scope. With
   // nothing selected, a drag must leave the selection empty rather than

frontend/src/stimulus/controllers/dynamic/sortable-lists/item.controller.spec.ts

@@ -1344,6 +1344,7 @@ describe('Sortable lists item controller', () => {
         moveInDirection: vi.fn(),
         moveAvailability: vi.fn(() => null),
         ownerListElementOf: vi.fn(() => null),
+        ownerRowsContainer: vi.fn(() => null),
         collapseSelectionForDrag,
       };
 

frontend/src/stimulus/controllers/dynamic/sortable-lists/selection.ts

@@ -87,9 +87,11 @@ function listRowsContainer(list:HTMLElement):HTMLElement {
 }
 
 // The id of the item a row holds, whether the row is the item element or
-// merely contains it.
-function rowItemId(row:Element):string|null {
-  const item = resolveItemElement(row);
+// merely contains it. Bounded by the rows container: resolveItemElement's
+// querySelector fallback descends unbounded, so a section row would otherwise
+// resolve to the first field of the list nested inside it.
+function rowItemId(row:Element, rowsContainer:Element):string|null {
+  const item = resolveItemElement(row, rowsContainer);
 
   return item ? resolveItemId(item) : null;
 }
@@ -189,7 +191,7 @@ export function resolveRangeIds(
 
   const rowsContainer = listRowsContainer(list);
   const rows = Array.from(rowsContainer.children);
-  const anchorRow = rows.find((row) => rowItemId(row) === anchor.id);
+  const anchorRow = rows.find((row) => rowItemId(row, rowsContainer) === anchor.id);
   // Meaningful only because rowsContainer came from the list rather than from
   // the candidate's own parent: a candidate whose item sits outside the rows
   // container (nested in some other part of the list) has no row here.
@@ -204,7 +206,7 @@ export function resolveRangeIds(
 
   const ids:string[] = [];
   for (const row of span) {
-    const item = resolveItemElement(row);
+    const item = resolveItemElement(row, rowsContainer);
     const id = item ? resolveItemId(item) : null;
     // A structural row inside the span (a truncation marker) is a hard
     // boundary, and so is a card the user cannot move — but the two are not